WO2011073486A1 - Solid-state dye laser - Google Patents

Abstract

This invention patent describes a system based on organic dyes incorporated into a solid matrix able to emit narrow-linewidth tuneable laser radiation in the green-red region of the electromagnetic spectrum, for optoelectronic and biophotonic applications. The system comprises the dispersive or non-dispersive laser cavity, and the active means used to generate and emit laser light. The active means includes at least one dye included in a solid matrix of at least one polymer. In non-dispersive cavity each dye-matrix emits wideband radiation at a specific central wavelength. In dispersive cavity each dye-matrix combination emits narrowband radiation that can be tuned over a range of at least 40 nm.

Description

 SOLID STATE COLORING LASER

OBJECT OF THE INVENTION The present application is a certificate of addition of the application P200802558, filed on September 5, 2008. The main application describes a procedure for removing pigment spots and tattoos on the skin by means of a laser dye system in state solid, as well as the laser and the active medium used to carry out said procedure. The present application is directed, in a general manner, to a solid state dye laser system, as well as to an active medium formed by synthetic polymers suitable for laser generation in the green-red region of the spectrum. PREVIOUS TECHNIQUE

Currently, synthetic polymers are used in many applications in various fields, including in the field of Optics. A characteristic of synthetic polymers is their behavior as an insulator, both thermal, as well as electrical and acoustic, characteristics that in turn are fundamental in a whole series of applications of these materials. It is precisely this insulating character that determines the margins of use of synthetic polymers in those optical applications in which the light incident on them is partially absorbed, either directly, by some chromophore present in the polymer structure, or indirectly, through some additive incorporated into it. In both cases, the part of the absorbed energy that is released to the medium in the form of heat has the disadvantage of its poor dissipation, as a consequence of the insulating nature of these materials, which can lead to thermal degradation, and / or of the additives incorporated therein, as a consequence of the high temperatures reached locally in the areas where the light falls. This drawback is therefore a limiting factor when using synthetic polymers as solid matrices in certain optical components, such as optical filters, waveguides and solid-state dye lasers, among others, with thermal stability being a determining factor of the possible use of these materials on an industrial and commercial scale.

Dye lasers are used today in very diverse fields, both in industry and in Medicine. However, the use of these dye lasers implies the use of a dye in liquid solution, which entails a series of drawbacks and limitations: - the need to use large volumes of organic solvents, some of which are toxic, volatile and flammable;

 - have to maintain a constant and uniform flow of these solutions within the laser cavity;

 - having to periodically renew the solution of the dye, when it degrades during its continued use, or replace it when the emission wavelength needs to be changed;

- tedious operations that occur when cleaning the cavity and eliminating said solutions, without forgetting the complexity of the design and the auxiliary instrumentation that forces the pumping of said solutions to the laser cavity.

In order to overcome these inconveniences, a considerable international research effort has been made, aimed both at the study of the photophysical and photochemical processes put into play when the laser dyes are in a solid medium, as to the synthesis of new dyes and more efficient laser materials and, thermally and photochemically, more stable. Although a wide variety of materials such as matrices of laser dyes have been studied, such as low temperature solidified solvents, jellies, molecular organic crystals, inorganic glasses ..., it has been the polymers (organic and organic-inorganic hybrids) that present better potential to be operational at industrial and commercial level, as demonstrated by the work and results achieved during the last decade (A.Costela, I. García-Moreno, R. Sastre, Materials for solid-state dye lasers, in Handbook of Advanced Electronic and Photonic Materials and Devices, Ed. H. Nalwa, Academic Press, San Diego, CA, USA, 2001; A. Costela, I. García-Moreno, R. Tailor, Solid-state dye lasers, in Tunable Laser Applications , Second Edition, Ed. FJ Duarte, CRC Press, Boca Raton, Florida, USA, 2009).

One of the directions of work followed to improve the photostability of these materials has consisted in the development of a whole series of new polymeric matrices, linear and crosslinked, in which by co-polymerization we introduced covalently the dye molecules, thus improving the Shelf life of these new lasers, as well as all the advantages outlined above for solid state dye lasers (ES 9501419, 1995 and USA 6,281,315 2001). Likewise, a systematic study has been carried out on the structural modification of the substituents of dipyrrometic dyes, with the aim of improving their properties and their photostability. To this end, we focus our efforts on establishing the effect of the substitution at position 8 of the pyromethenic ring, initially introducing both acetoxypolymethylene groups and methacryloxypolymethylene groups, which were used as dyes Laser models and monomer laser dyes. These new dyes presented, both in liquid solution and in solid matrices, a better laser efficiency and a remarkable higher photostability, than the corresponding commercial laser dyes when they were covalently bound to a polymer (ES 009901540; A. Costela., I. García- Moreno, C. Gómez, F. Amat-Guerri, M. Liras, R. Sastre, Efficient and highly photostable solid-state dye lasers based on modified dipyrromethene.BF2 complexes incorporated into solid matrices of poly (methyl methacrylate), Appl. Phys B, 76, 365, 2003, and M. Álvarez, F. Amat-Guerri, A. Costela, I. García-Moreno, C. Gómez, M. Liras, R. Sastre, Linear and crosslinked polymeric solid-state dye Lasers based on 8- substituted alkyl analogs of Pyrromethene 567, Appl. Phys. B, 80, 993, 2005). Next, we also incorporate in said position 8 of the indacenic ring, only a p-phenylene-acetoxypolymethylene group and a p-phenylene-methacryloxypolymethylene group, whose photophysical properties and their laser evaluation demonstrated that, both in liquid solution saturated in air, as in its solid copolymers with methyl methacrylate, its laser emission efficiencies and photostability were markedly improved (I. García-Moreno, A. Costela, L. Campo, R. Sastre, F. Amat-Guerri, M. Liras, F López-Arbeloa, J. Bañuelos, I. López-Arbeloa, 8- Phenyl-Substituted Dipyrromethene.BF2 Complexes as Highly Efficient and Photostable Laser Dyes, J. Phys. Chem. A, 108, 3315, 2004). These properties were further improved by incorporating substituents in the 8-position of the indacenic ring incorporating di-phenylene and p-triphenylene groups (ES 200701763; M. Álvarez, A. Costela, I. García-Moreno, F. Amat-Guerri, M. Liras , R. Sastre, F. López Arbeloa, J. Buñuelos Prieto, I. López Arbeloa, Photophysical and Laser Emission Studies of 8- Polyphenylene-Substituted BODIPY Dyes in Liquid Solution and in Solid Polymeric Matrices Photochem. Photobiol. Sci., 7, 802, 2008) as well as the double covalent anchoring of the dye to the matrix, by significantly reducing its non-radiative emission processes (I. García- Moreno, F. Amat-Guerri, M. Liras, A. Costela, L. Infantes, R. Sastre, F. López Arbeloa, J. Bañuelos Prieto, I. López Arbeloa, Structural Changes in the BODIPY Dye PM567 Enhancing the Laser Action in Liquid and Solid Media, Adv. Funct. Mater. 17, 3088, 2007).

Trying to improve the thermal properties of these polymeric matrices, new organic-inorganic hybrid polymers were also developed, obtained by simultaneous polymerization-polycondensation synthesis procedures, which have allowed to achieve even greater photostabilities (A. Costela, I. García-Moreno, C. Gómez, O. García, L. Garrido, R. Sastre, Highly efficient and stable doped hybrid organic-inorganic materials for solid-state dye lasers, Chem. Phys. Lett. 387, 496, 2004; A. Costela, I García-Moreno, C. Gómez, O. García, R. Sastre, Enhancement of laser properties of pyrromethene 567 dye incorporated into new organic-inorganic hybrid materials, Chem. Phys. Lett. 369, 656, 2003; A. Costela, I. García-Moreno, C. Gómez, O. García, R. Sastre, Environment effects on the lasing photostability of Rhodamine 6G incorporated into organic-inorganic hybrid materials, Appl. Phys. B 78, 629, 2004; A. Costela, I. García-Moreno, O. García, D. del Agua , R. Sastre, Structural influence of the inorganic network in the laser performance of dye-doped hybrid materials, Appl. Phys. B. 80, 749, 2005; I. García- Moreno, A. Costela, A. Cuesta, O. García, D. del Agua, R. Sastre, Synthesis, Structure, and Physical Properties of Hybrid Nanocomposites for Solid-State Dye Lasers, J. Phys. Chem. B 109 , 21618 2005; O. García, L. Garrido, R. Sastre, A. Costela, I. García-Moreno, Synthetic Strategies for Hybrid Materials to Improve Properties for Optoelectronic Applications, Adv. Funt Mater. 18, 2017, 2008). Trying to reduce the times and difficulty of synthesis of these hybrid materials while increasing their reproducibility and their thermo-optical and mechanical properties, other new organic-inorganic hybrid polymers were obtained from mesoporous or aerogels, consisting of three-dimensional networks of open pore silica of nanometric size, which are flooded with appropriate laser dye-monomer formulations, to be subsequently polymerized in situ, in a controlled manner, thus allowing to obtain highly photostable materials, mainly when the polymers obtained within the Mesoporous silica matrix were fluorinated in nature (A. Costela, I. García-Moreno, C. Gómez, O. García, R. Sastre, A. Roig, E. Molins, Polymer-Filled Nanoporous Silica Aerogels as Hosts for Highly Stable Solid-State Dye Lasers, J. Phys. Chem B 109, 4475, 2005; O. García, R. Sastre, D. del Agua, A. Costela, I. García-Moreno, A. Roig, Efficient optical materials based on fluorinated-polymeric silica aerogels, Chem. Phys. Lett. 427, 375, 2006).

The main advantage of the incorporation of silica in these materials lies in the substantial improvement of its thermal conductivity, which favors the dissipation of local heat released during the process of excitation or pumping of the dye, thus avoiding, to a large extent, degradation thermal of the dye and, therefore, lengthening the service life of the laser generator. However, in both families of these organic-inorganic hybrid polymers, although silica is homogeneously distributed in the final material, the domains of this inorganic phase can give rise to undesirable phenomena in terms of their interference with light, as well as the dye segregation of said domains, which remains dissolved only in the domains of the organic polymer.

Therefore, and considering also the difficulties of synthesis that both families of polymers present, we consider for these applications the synthesis of new polymers in which we incorporate silica at the molecular level, in order to obtain intrinsically more homogeneous materials in order to obviate these inconvenience and improve even more its thermal conductivity and its optical properties. One approach was to use organic compounds with silicon atoms incorporated directly into its structure. In this way, the matrix would remain organic, which means plasticity and a simpler method of synthesis, but with better thermal properties due to the presence of silicon atoms. With this approach we managed to maintain the efficiency in the laser emission with a notable increase in stability, with the laser emission remaining stable after 700,000 pulses of pumping in the same position of the sample at a repetition rate of 30 Hz, with energy per 3.5 mJ pumping pulse (A. Costela, I. García-Moreno, D. del Agua, O. García, R. Sastre, Highly photostable solid-state dye lasers based on silicon-modified organic matrices, J. Appl. Phys 101, 0731 10, 2007). More recently, and following this same approach, we have proceeded to develop materials based on silylated copolymers with silsesquioxane groups (ES 200800220; O. García, R. Sastre, I. García-Moreno, V. Martín, A. Costela, New laser hybrid materials based on POSS copolymers, J. Phys. Chem. C, 1 12, 14710, 2008), where the laser emission further increases its stability and efficiency increases significantly, regardless of the nature of the chromophore used. With these new photosensitive materials, a universal component that optimizes the laser action of different dyes has been obtained. All these results and developments allow to obtain materials that are already sufficiently efficient and stable to be used at industrial and commercial level, as active means for the emission of laser light. Based on all this knowledge and results, we consider of great interest the development of a new laser, object of the present patent, with finely tunable multichromatic emission, capable of emitting at different wavelengths within the green-red region of the spectrum, with applications in Optoelectronics and Biophotonics.

DESCRIPTION OF THE INVENTION

In the light of the current knowledge and developments achieved in the field of solid state dye lasers, described above, it is of great interest applied to have this type of lasers, with tunable emission at different wavelengths, according to the laser dye used.

Some of the most important applications of lasers depend mainly on the wavelength of their emission, which is why it is of great interest and utility to develop a multichromatic laser based on these materials capable of emitting tunable laser light at different wavelengths that cover the green-red range of the visible spectrum. Other applications, for example in the field of spectroscopy, require that the emitted radiation be of small spectral width and finely tunable.

The main object of the present invention is a solid state dye laser based on the materials described above that meets both requirements: radiation emission at different wavelengths in the green-red region of the visible spectrum, which can be generated with small spectral width and fine tuning. The temporal duration of the emitted laser pulses can be shortened by using in the developed laser system saturable absorbers based on the same materials responsible for the laser emission, which provides a further degree of flexibility to the system. materials

The active medium for the generation and emission of laser radiation in the system referred to in the present invention is characterized in that it comprises at least one dye included in a solid matrix of at least one polymer, each dye-matrix combination emitting at a length of concrete wave within the green-red region of the spectrum. That is, the active medium will comprise as many combinations of a dye with a solid matrix as wavelengths are selected for laser application.

Since there is currently no universal matrix capable of being able to be used with any laser dye, it is necessary, first, to adapt and optimize a matrix for each laser dye chosen. Preferably, the polymers that make up the matrix or matrices of the present invention are selected from linear and cross-linked synthetic polymers. More specifically, the polymers are selected from those obtained from the monomers of the group comprising: methyl methacrylate, 2-hydroxyethyl methacrylate, pentaerythritol tetracrylate, trifluoromethyl methacrylate, pentaerythritol triacrylate, 2-hydroxyethyl acrylate and methacrylate -silyl-propyl, and combinations thereof. And more specifically, each of the solid matrices has a composition selected from: methyl polymethacrylate; copolymer of hydroxyethyl methacrylate with methyl methacrylate, crosslinked with pentaerythritol tetracrylate; copolymer of methyl methacrylate with trifluoromethyl methacrylate; copolymer of methyl methacrylate with pentaerythritol triacrylate; 2-hydroxyethyl polymethacrylate; and hydroxyethyl methacrylate copolymer with triethoxymethyl silyl propyl methacrylate. Where appropriate, the characteristics of the laser emission are optimized by incorporating silica nanoparticles based on silsexquioxane monomers. The choice of dyes was carried out by ensuring that, in addition to having appropriate efficiencies and stabilities, the emission wavelength covers at least the range of 540 to 700 nm between all the dyes chosen. Preferably, the dyes used belong to the family of pyrometenes, perilenes, rhodamines, LDS or a combination thereof. More preferably, the dyes used are selected from Pirrometene 567, Pirrometene 597, Rhodamine 6G, Perylene 240, Perylene 300, Sulphordamine B, Rhodamine 640, LDS 698, LDS 722 and LDS 730.

The first criterion for the selection of a solid state laser matrix is that said matrix does not have absorption at the absorption and emission wavelengths of the chosen dye, or at the pumping or excitation wavelength. The second criterion, which is exclusive, is that of the solubility of the laser dye chosen in said matrix. For this purpose, it can be used as a guide to check the prior solubility of the dye in the monomer or mixture of monomers, at the appropriate concentration to obtain a total absorption at the excitation or pumping wavelength (s). Then, in the case of achieving the desired solubility, the solution of the dye in the monomer, or mixture of monomers, is treated with ultrasound, to maximize its solubility, and subsequently the resulting solution is ultrafiltered, using 0 membranes, 2 microns, in anticipation of possible solid impurities in the environment. Subsequently, the controlled polymerization of said solution is carried out, by choosing, in each case, the most appropriate experimental conditions following the procedures, methods and conditions described in our Spanish Patents 2 161 152, 2001 and ES 200800220, 2008. A Once the matrices carrying the laser dyes are obtained in the appropriate proportions and concentrations, they are machined and polished, following the procedures usual in the machining of materials, until reaching the desired geometric shape and dimensions, checking, visually and spectroscopically, if the chosen dye is also soluble in the final polymer or copolymer obtained.

Once these two requirements have been met, the corresponding evaluation of their laser properties and, when necessary, also of their photophysical, photochemical, thermal and optical properties can be carried out. The main laser parameters that define a usable material as an active medium in the generation of laser light are: its emission efficiency or performance; its photostability or life time in service and its tunability or wavelength range of laser emission. For the evaluation as an active medium for the generation of laser radiation of the new materials, different assemblies of those commonly used in known laser devices can be used, although in the present case the two described in our Spanish Patent 2 161 152, 2001 are recommended , as well as the cavities, pumping system and detailed procedures therein. Among all the combinations of matrices and dyes evaluated, only those with the best results were obtained to cover the range of wavelengths in the region of the visible spectrum that ranges from green to far red. In the attached figure 1 the laser spectra of some of the new dye matrices are shown, and where the overlapping of said emissions can be observed within the area of interest. In particular, the plot represents laser intensity versus wavelength in the range from green to red. These materials, once conveniently polished and with the proper geometric configuration, were introduced into a cavity designed to selectively excite or pump each of these matrices, using for this purpose an external source of polychromatic or monochromatic light, coherent or non-coherent .

In summary, in the attached Table 1, the main laser parameters of the preferably selected materials, pumped transversely at 532 nm, are collected. Table 1 specifies the preferred concentrations used for the dyes and the preferred combinations for the composition of the corresponding matrices in which the dyes are incorporated.

TABLE 1

Photo stabilized

Efficiency λ

 D interval

Laser dye and cia emisi

 tunable after polymer matrix * laser ón

 d (nm) 100,000

(%) (nm)

 pulses (%)

Pirrometene 567 [1, 5x10 ^"3

 M] 60 568 545-585 100 p (MMA + 8MMA POSS)

Pirrometene 597 [6x10 ^"4 M]

 63 583 565-620 100 P (MMA + 8MMAPOSS)

Rhodamine 6G [4x10 ^"4 M]

cop (HEMA / MMA 1/1 + 42 576 557-605 98

8MMAPOSS)

Rhodamine 640 [5x10 ^"4 M]

cop (HEMA / MMA 1/1 + 47 640 620-660 96

8MMAPOSS) Sulphordamine B [4x10 ^"4 M]

cop (HEMA / MMA 1/1 + 43 608 575-645 100 8MMAPOSS)

Red Perylene [5x10 ^"4 M]

 27 618 605-655 100 p (MMA + 8MMAPOSS)

LDS698 [4x10 ^"4 M]

 25 660 635-695 80 P (HEMA + 8MMAPOSS]

LDS 722 [4x10 ^"4 M]

 28 674 650-720 86 p (HEMA + 8MMAPOSS)

LDS 730 [8x10 ^"4 M]

 21 730 690-750 100 p (HEMA + 8MMAPOSS)

* P (MMA) = methyl polymethacrylate

 * cop (HEMA MMA 1/1) = hydroxyethyl methacrylate copolymer with methyl methacrylate in volume ratio 1 to 1.

 * p (HEMA) = polyhydroxyethyl methacrylate.

 * 8MMAPOSS = in each case the matrix contains a 13% weight ratio of octa (methyl methacrylate) -silsesquioxane.

Laser system

The present invention also relates to a solid state dye laser radiation system based on the described materials, with tunable emission in the green-red region of the spectrum, comprising at least the following devices:

- a cavity, in which the active medium comprising at least one dye included in a solid matrix of at least one polymer defined above is located;

- a source of excitation-pumping of the active medium; Y - a wavelength tuner mechanism.

As a source of excitation or pumping light, a coherent or non-coherent, ultraviolet or visible, monochromatic or polychromatic light emitter can be used, although preferably an Nd: YAG laser should be used, it being convenient to use its emission, folded in frequency, at 532 nm, with repetitive pumping speeds between 1 Hz and 10 KHz, and energies between 0, 1 and 50 millijoules.

 The cavity or oscillator, contains the matrix with the laser emitting dye with a geometric configuration suitable to one of the two possible types of pumping: transverse or longitudinal. In turn, the oscillator can be dispersive or non-dispersive. In transverse pumping, the preferred geometric configuration of the dye-matrix, among all possible ones, is a cylinder 1 cm high and a diameter between four and 10 mm. Said cylinder must have a flat side face parallel to its axis between 1 and 6 mm. Both that side face and the bases of the cylinder must be polished, at least, up to optical quality.

Preferably, a pair of cylindrical lenses can be used for transverse focusing of the pumping beam on the flat face parallel to the axis of the matrix, in order to achieve a rectangular irradiation spot of 10 mm between 1 and 3 mm.

In the cavities for non-dispersive transverse pumping, a conventional mirror, of polished aluminum, is used, which we will call the rear mirror, as a reflective element, placing it in parallel, about 2 cm from one of the faces of the cylinder, in order to minimize the dimensions of the cavity. This cavity closes with a glass window, arranged parallel to the mirror at a distance of approximately 1 cm from the other side of the cylindrical sample. Where appropriate, the role of the glass window can be exerted by the face of the solid sample farthest from the rear mirror.

Therefore, when the pumping over the solid dye-matrix combinations is transverse, the cavity must comprise at least:

- a pair of cylindrical lenses to focus the excitation-selectively pumping beam on one of the dye and solid matrix combinations;

- a conventional mirror of polished aluminum as a reflective element; Y

- a glass window that closes the cavity, arranged parallel to the mirror. Where appropriate, each of the sample farthest from the mirror can play the role of the window as a closing element of the cavity.

This generates laser radiation with a spectral width of a few nanometers.

In the cavities for dispersive transverse pumping, wavelength selector elements are incorporated into the cavity. In a configuration, known as a configuration with diffraction network with flush incidence (Figures 2a and 2b), a diffraction network is incorporated into the cavity, located after the cylindrical sample in a position such as normal to the surface of the network form an angle between 87 ° and 89 ° with the axis defined by the normal to the surface of the rear mirror (cavity axis). The radiation that affects the diffraction network coming from the sample along the axis of the cavity, it is dispersed by the diffraction net in its different orders. A fully reflective mirror, called a tuning mirror, is arranged perpendicular to the direction defined by the order 1 of the diffraction network, so that it retro-reflects the laser radiation that affects it dispersed by the diffraction network in its order 1 . In the so-called open cavity (Figure 2a) the rear mirror is fully reflective, and the laser emission is obtained in the direction corresponding to the zero order of the diffraction network. In the closed cavity (Figure 2b) the laser emission is obtained through the rear mirror, which transmits a fraction of the laser radiation that oscillates inside the cavity. This rear mirror can be either a mirror with a partially reflective coating at the wavelength of the laser, or a Glan-Thompson polarizer with an anti-reflective coating on the inner surface and a partially reflective one on the outer surface.

A second configuration is known as the configuration with diffraction network in Littrow assembly (Figures 3a and 3b). The cavity consists of a rear mirror, shows with the dye, one or two prisms to expand the beam and a diffraction network in Littrow assembly, that is, with the normal to the surface of the diffraction network forming an angle such that, In the first order, the incident radiation in the network is reflected back along the axis of the cavity. The prisms are used to expand the radiation beam and illuminate the largest possible extent of the diffraction network to improve the spectral resolution. The rear mirror has the same characteristics as in the configuration with the diffraction network in flush incidence. In these dispersive cavities the generated laser radiation has a spectral width in the range of thousandths of a nanometer. In longitudinal pumping, the preferred geometric configuration of the matrix with the dye, among all the possible ones, is a disc of thickness greater than 1 mm and of variable diameter, preferably greater than 10 mm. The pumping or excitation of the sample occurs according to the axis of the cavity, so that it is co-linear with the laser emission. A conventional spherical lens focuses the pumping beam on the sample and two dichroic mirrors form the cavity. The input is transparent to the pumping radiation and fully reflective to the laser radiation emitted by the sample. The output is fully reflective of the pumping radiation and partially reflective of the laser radiation emitted by the sample.

The choice of the central emission wavelength of this laser system, within the green-red region of the spectrum, is achieved by using the materials described in Table 1, selecting in each case the corresponding dye-matrix according at the desired wavelength. When the samples are incorporated into a non-dispersive cavity, the wavelength emitted by each material remains fixed, at the value indicated in the table above. Using a dispersive cavity, the tunable ranges indicated in the table are covered with each sample.

Sample selection can be done manually or automatically. In the first option, to manually replace the dye-matrix emitting element with another, it is only necessary to have within the cavity a support adapted to the geometric configuration of the dye-matrix emitting element, so that a piece can easily be replaced by other and that said support does not interfere with the light of the excitation or pumping beam, nor with the emission beam of the dye-matrix piece. To do this, any fixation that meets this requirement can be used, as well as ensuring the reproduction of the position when changing a piece by another, and thus avoid realignment after each change or replacement operation of the emitting element. As an example, a simple support can be used in Figures 4a and 4b that can be used in the transverse pump configuration.

In the case of a longitudinal pumping configuration, the simplest fixation of the sample can be a rod that crosses the disk through its geometric center. For the automatic exchange of laser parts, different mechanisms and automatisms can be used from those available today in the field of Optics. For this specific application, a revolver or ferris wheel type device would be suitable, housing each cylinder (transverse pumping) or disk (longitudinal pumping) in a circular manner around the central axis of the device, as shown in Figures 5a and 5b attached.

To change one sample for another, you just have to rotate the revolver or ferris wheel around its axis, until the new sample of coloring polymer is positioned in the correct position inside the cavity. The operation can be automated using a stepper motor that acts as a micropositioner, so that its use and handling can in turn simply be integrated, for example, into the program for controlling the frequency of shots and laser output energy.

In all of the above, the emitting element remains static during the excitation or pumping process. However, a substantial improvement in the duration of the laser system, object of this patent, can be achieved if the dye-matrix emitting element moves during the excitation operation. Since in the static system the excitation and generation of the laser light takes place only in a small volume element, the rest of the total volume of the piece remaining completely unchanged, therefore, the rest of the active material can be used by simply incorporating a dynamic mechanism into the laser system that moves the sample, in a controlled way, during operation of the system. Thus, in a preferred embodiment, the excitation-pump source moves during the excitation stage, keeping the active medium fixed. In another preferred embodiment, the active medium moves vertically or horizontally during the excitation-pumping stage, keeping the excitation source fixed.

In the case of disc-shaped samples (longitudinal pumping), by simple rotation of the shaft that supports them, with regulation of their rotation speed in proportion to the frequency or speed of pumping of the excitation laser. If it is considered necessary or convenient, to take advantage of the entire active surface of the disk, a scan can also be done using a scanner of the pump laser beam, which would move the beam in one position per turn, in a scanning sweep of the beam from the inside the disc towards its outside and vice versa, until after the continuous use of the laser the efficiency or performance of that piece reached a minimum value.

In the case of cylindrical samples (transverse pumping), a scan can also be done with the beam of the pumping laser on the side face of the sample, which would remain static, or the cylindrical sample is rotated on its central axis, at the appropriate speed and proportional to the frequency of the excitation beam, which in this case would remain static.

A design that allows to obtain multiple emission, in several laser beams, for multiplexing applications, consists in using a lens with several focuses to achieve multiple focusing of the pumping beam on the sample. A lens with three focuses would define three irradiated areas in the sample, which would cause laser emission in three differentiated beams (Figure 6).

Applications

As described above, in the section of the State of the Art, the use of dye lasers in the field of Medicine has allowed the development of new innovative therapies. One of the main reasons, although among many others, for which the use of the laser has achieved a remarkable success in its medical applications, lies in the selective effect of the wavelength, for each specific application. Dye lasers are especially suitable for providing different wavelengths. However, as also stated in the section of the State of the Art, the use of the usual dye lasers, of liquid state, in a medical or industrial environment presents many drawbacks due to the complexity and inherent risks to the health that entails the use of dyes in liquid phase. The alternative proposed here, aimed at resolving this limitation, and object of the present Invention Patent, allows to select the desired wavelength within the wavelength range of the visible spectrum, manually or automatically, for direct application, by the use of materials doped with dyes in solid phase. One of the applications that demonstrates the versatility of this new laser system is that of Photodynamic Therapy. Photodynamic Therapy is a non-invasive, or minimally invasive, procedure that uses photosensitizing substances that, once administered to the patient, are selectively retained in the diseased tissue and can be activated under irradiation with intense visible light to cause selective photochemical destruction of the diseased cells Usually, The photosensitizing substance is activated by the use of light with adequate wavelength that generates a cytotoxic cytotoxic reaction mediated by singlet oxygen. Therefore, dye lasers with their ability to generate specific wavelengths within the visible spectrum are especially suitable for this application.

For this application, the solid state dye laser is used with the non-dispersive transverse pumping cavity, since it is not necessary for the laser radiation to be especially narrow in bandwidth. The modus operandi consists, first of all, in selecting the emitting element that emits at the wavelength at which the photosensitizer used in the treatment absorbs. Thus, for example, some usual photosensitizers are Photofrin, which absorbs at 630 nm, ALA, which absorbs at 635 nm or different porphyrins, which absorb around 652 nm. Once the laser emitting element is placed inside the cavity, manually or mechanically, the laser light is conducted to the area to be treated by means of optical fiber systems.

In spectroscopy applications, the solid state dye laser with the dispersive cavity is used. The known laser-induced fluorescence cone technique (denoted by the acronym LIF, corresponding to the name of the technique in English) is based on the fact that fluorescent species can absorb light at a frequency and then re-emit it (emit fluorescence) at a frequency different, lower. This procedure is used to study the structure of the molecules or for selective detection of species. It is important that the excitation wavelength be selected so that it is strongly absorbed by the species that radiates. It is in this aspect where the solid state dye laser with dispersive cavity has a great competitive advantage due to its flexibility, which allows it to tune the radiation emitted exactly to the transition of the species under study which is intended to excite. In addition, the small spectral bandwidth generated by the dispersive cavity allows the excitation to be discriminated between levels of the irradiated species very close to each other. This specificity is of the greatest importance in fields such as, for example, the detection and quantitative measurement of concentrations of pollutants and gaseous species in the atmosphere.

A second example of application of the solid state dye laser with dispersive cavity is the resonant Raman spectroscopy. Raman spectroscopy is based on the inelastic dispersion of a beam of photons that affect the medium under study. In this inelastic process the absorbed photons are re-emitted with less energy. The difference in energy between absorbed and re-emitted photons corresponds to the energy needed to excite the molecules of the medium in a vibrational way above the starting level. In the resonant Raman spectroscopy the species to be studied is illuminated with laser radiation of small line width and the laser wavelength is adjusted so that the energy of the scattered light coincides with that of a transition of the species under study. Therefore, in this technique it is decisive to have tunable radiation of small line width, such as that provided by the solid state dye laser with dispersive cavity.

The same materials used as active medium in the solid state dye laser can be used as saturable absorbers to shorten the temporal duration of the pulses emitted by the laser systems described above. The implementation of this application is achieved by incorporating into the laser cavity an element with 1 or 2 mm thick disc or parallelepiped geometry. This element consists of a solid matrix based on the materials described above (organic copolymers, hybrids or incorporating silicon) with suitable dyes, such as pyrometene 597, rhodamine 640 or DODCI, in concentration such that the optical density of the solid element at the wavelength of the laser emission in the solid state is between 1 and 5. In this way the duration of the pulses emitted by the laser can be narrowed. solid state dye to the subnanosecond region.

EXAMPLES OF REALIZATION

As representative, but not limiting, examples of the materials object of this patent, some examples of their obtaining and properties are described below, as well as of the devices specifically developed for use as solid state dye lasers, and their evaluation and application. Example 1

 Synthesis of Polymers and Copolymers (Solid Matrices).

Among all the laser dyes known today, all those commercials of interest are selected in a first step, depending on their emission wavelength, their efficiency or performance in the emission of laser light, and their photostability

Once a specific laser dye is selected, solutions of between 0.5 and 2 mM are prepared in a monomer or in mixtures of two or three of the monomers chosen in varying proportions. Where appropriate, one of these monomers can be one of the silylates with silsesquioxane groups, such as 8MMAPOSS (octa (methyl methacrylate) -silsesquioxane), which is added in a proportion of 13% by weight. Once the solubility of the dye in the monomer mixture is ensured, 20 ml of this solution is taken. The initiator is added to each of these solutions azobisisobutyronitrile (20 mg; 0.12 mmol), which in turn is solubilized by stirring and subsequent treatment in an ultrasonic bath. Then, said solutions are microfiltered, first with a 0.45 micron membrane and then with another 0.2 micron pore size. The resulting solutions are poured onto cylindrical polypropylene molds with an inner diameter between 10 and 25 mm, within which they are deoxygenated by pure argon or nitrogen bubbling, submerging in these solutions a capillary for about ten minutes. The molds are closed and sealed under an inert atmosphere and kept at 40 ° C for 48 hours. After this time, the initial solutions will have solidified, then the temperature will rise to 45 ° for one day. The temperature is then increased to 50 ° C and then, in order to destroy the remains of the initiator that had not reacted, as well as to increase the degree of final conversion, the temperature is raised to 80 ° C for a period of one day. Finally, the temperature is reduced slowly (5 ° C / day) until it reaches room temperature, in order to avoid freezing of residual stresses that could affect the optical quality of the material obtained, then proceeding to unmold the pieces.

Example 2

Evaluation of the new final materials as emitters of laser radiation. The laser evaluation of the materials obtained according to the procedure described in the previous example, was carried out once conveniently machined and polished in the desired geometric shape according to the design of the laser cavity to be used. As an example, one of the devices described above, or the device described in the patent ES 009901540, can then be used for said laser evaluation, then forming the materials here obtained in the form of cylinders 1 cm high and 1 cm in diameter, with a parallel cut to its axis, in order to obtain a flat lateral surface.

Among all the materials evaluated were those whose efficiency and stability values were the highest among all tested for each wavelength, while at the same time seeking an overlap between their emissions, within the spectral region of interest.

Table 1 shows some of the materials developed, as well as the corresponding values of their laser parameters: efficiency, emission wavelength, emission interval and photostability, obtained following the procedure described in example 1.

TABLE 1.

 Laser parameters of the selected materials. Pumping Conditions: Transverse Pumping at 532nm, 10Hz; Energy: 5mJ / pulse, for 100,000 pulses in the same position.

Photo stabilized

Efficiency λ

 D interval

Laser dye and cia emisi

 tunable after polymer matrix * laser ón

 d (nm) 100,000 (%) (nm)

 pulses (%)

Pirrometene 567 [1, 5x10 ^"3

 M] 60 568 545-585 100 p (MMA + 8MMA POSS)

Pirrometene 597 [6x10 ^"4 M]

63 583 565-620 100 P (MMA + 8MMAPOSS) Rhodamine 6G [4x10 ^"4 M]

cop (HEMA / MMA 1/1 + 42 576 557-605 98 8MMAPOSS)

Rhodamine 640 [5x10 ^"4 M]

cop (HEMA MMA 1/1 + 47 640 620-660 96 8MMAPOSS)

Sulphordamine B [4x10 ^"4 M]

cop (HEMA / MMA 1/1 + 43 608 575-645 100 8MMAPOSS)

Red Perylene [5x10 ^"4 M]

 27 618 605-655 100 p (MMA + 8MMAPOSS)

LDS698 [4x10 ^"4 M]

 25 660 635-695 80 P (HEMA + 8MMAPOSS]

LDS 722 [4x10 ^"4 M]

 28 674 650-720 86 p (HEMA + 8MMAPOSS)

LDS 730 [8x10 ^"4 M]

 21 730 690-750 100 p (HEMA + 8MMAPOSS)

* P (MMA) = methyl polymethacrylate

 * cop (HEMA / MMA 1/1) = hydroxyethyl methacrylate copolymer with methyl methacrylate in volume ratio 1 to 1.

 * p (HEMA) = polyhydroxyethyl methacrylate.

 * 8MMAPOSS: 8MMAPOSS: in each case the matrix contains a 13% weight ratio of octa (methyl methacrylate) - silsesquioxane

The results obtained in efficiency, tunability and photostability demonstrate the feasibility of using these new materials as laser light emitters, object of the present invention patent. Example 3

 Laser system with wavelength selector

Said laser system consists of the elements and devices described below.

As a source of excitation or pumping light, an Nd: YAG laser is used, with emission, doubled in frequency, at 532 nm, repetitive pumping speeds between 1 Hz and 10 KHz, and energies between 0, 1 and 50 millijoules

As a cavity, for transverse pumping, a dye-matrix configuration consisting of a cylinder 1 cm high and a diameter between four and 10 mm is used. Said cylinder must have a flat side face of 10X4 mm. Both that side face and the bases of the cylinder must be polished to optical quality. A pair of cylindrical lenses were used for transverse focusing of the pumping beam on the flat face parallel to the axis of the matrix, which allows to obtain an irradiation area of 10 mm between 1 and 3 mm.

When the cavity is non-dispersive, a conventional mirror, of polished aluminum, is used as a reflective element, placing it in parallel, about 2 cm from one of the faces of the cylinder and a glass window, arranged parallel to the mirror at a distance of approximately 1 cm from the other side of the cylindrical sample.

The choice of the central emission wavelength of this laser system, within the green-red region of the spectrum, is achieved by using the materials described in Table 1, selecting in each case the corresponding dye-matrix of according to the desired wavelength. To this end, said selection can be made manually or automatically.

To manually replace the dye-matrix emitting element with another, it is only necessary to place it inside the cavity, in a support adapted to its geometric configuration as a counter-mold, which ensures its fixation and reproduction of the position when changing a piece on the other (Figures 4a and 4b). For the mechanical exchange of said elements a revolver or ferris wheel type device is used, where different dye-matrix cylinders are housed, as shown in Figure 5 (b).

To change one sample for another, you just have to rotate the revolver or ferris wheel around its axis, until the new sample of coloring polymer is positioned in the correct position inside the cavity. This operation can be automated using a stepper motor that acts as a micropositioner, so that its use and handling can in turn simply be integrated, for example, into the program for controlling the frequency of shots and laser output energy.

With this device, the desired central wavelength can be selected, according to the emissions of the available dye-matrix cylinders.

When it is desired to obtain tunable emission of small spectral width, a dispersive cavity is used, according to the scheme presented in Figure 2. The sample is placed between the rear mirror and the diffraction net, 3 cm from each of these elements. The rear mirror is aluminum, fully reflective and 1 cm in diameter. The diffraction net is holographic, 1200 lines / mm and has dimensions of 5 cm x 1 cm. The tuning mirror is placed 5 cm from the diffraction net, is fully reflective aluminum and has dimensions of 5 cm x 1 cm. The laser emission occurs in the direction corresponding to the zero order of the diffraction network. By placing a sample with a particular dye inside the cavity, laser emission is obtained with a line width in the range of thousandths of a nanometer, tunable over 30-40 nm, depending on the dye, as shown in Figure 1. Example 4

 Damage threshold of new materials for use as saturable absorbers.

When the new materials are incorporated into the laser cavity for use as saturable absorbers to shorten the temporal duration of the pulses emitted, they must withstand the high intensities typical of the laser radiation oscillating within the cavity. The ability of these materials to withstand high intensities was investigated by subjecting them to pulses of 60 and 160 femtoseconds (fs), at wavelengths of 800 and 400 nm, at repetition rates of up to 1 kiloherzio (kHz), and with energies comprised between 30 microjoules and 1, 4 millijoules. The samples were transparent at 800 nm and had optical densities in the range 0.8 to 3.7 at 400 nm. With pumping at 800 nm with pulses of 60 fs and repetition speed of 1 kHz, a sample of PM567 does not experience damage at intensities below 80 GW / cm ² . When rhodamine 640 or PM597 is used at intensities below 80 GW / cm ² (gigawatts per square centimeter) no damage occurs, but the transmitted radiation appears focused, indicating the existence of nonlinear phenomena. In rhodamine 640 the radiation is transmitted uniformly, while in the PM597 does it in discrete beams. At 84 GW / cm ^2, white light begins to be generated in the PM597, a clear indication that nonlinear phenomena dominate at these intensities. In rhodamine 640 no damage appears up to an intensity of 100 GW / cm ² .

Using 400 nm radiation in pulses of 60 fs at a repetition rate of 1 kHz, a sample of PM597 with an optical density of 3.7 is not damaged until an incident intensity of 21 GW / cm ² . This same intensity does not damage a rhodamine sample 640 with optical density of 0.8. Since in all the cavities that are used in the solid state dye laser object of this patent the radiation intensities are much lower (not exceeding 6 GW / cm ² ), the ability of the new materials to be Used in pulse shortening applications.

DESCRIPTION OF THE FIGURES

Figure 1. Laser spectra of some of the solid dye-matrix combinations developed in the present invention that form an active means for the generation of laser light.

Figures 2a and b. Tunable laser cavity in configuration with diffraction network with flush incidence: (a) open cavity; (b) closed cavity.

Figure 3a and b. Tunable laser cavity in configuration with diffraction network in Littrow assembly: (a) cavity with a prism; (b) cavity with two prisms. Figures 4a and b. Simple support for the fastening of the laser samples and their manual exchange in the cross-pumping configuration. Figures 5a and b. Design of a revolver or ferris wheel type device for automatic sample exchange: (a) sample holder for longitudinal pumping; (b) sample holder for transverse pumping.

Figure 6. Scheme representing the multiple focusing of the pumping beam on the sample in the case of a lens with three focuses, defining three areas of irradiation and laser emission in three differentiated beams.

Claims

1. Solid state dye laser radiation system, characterized in that it emits tunable laser radiation, discretely or continuously, in the green-red region of the electromagnetic spectrum, and which comprises at least the following elements:  - a cavity in which an active medium is located comprising at least one dye included in a solid matrix of at least one polymer.  - a source of excitation-pumping of the active medium, and - a wavelength tuner mechanism. 2. Laser radiation system according to claim 1, wherein the excitation-pumping source comprises at least one light emitter having the characteristics a), b), c) and d), each being selected from the two options given:  a) ultraviolet and visible;  b) monochromatic and polychromatic;  c) coherent and non-coherent; Y  d) continuous and pulsed. 3. Laser radiation system according to claim 2, wherein the excitation-pumping source comprises at least one visible, monochromatic, coherent and pulsed light emitter. 4. Laser radiation system according to any one of claims 1 to 3, wherein the excitation-pump source moves during the excitation stage, keeping the active medium fixed. 5. Laser radiation system according to any of claims 1 to 3, wherein the active medium moves vertically or horizontally or rotates during the pumping excitation stage, keeping the excitation source fixed. 6. Laser radiation system according to any one of claims 1 to 5, comprising a non-dispersive cavity which in turn comprises:  - a pair of cylindrical lenses to focus the excitation-selectively pumping beam on one of the dye and solid matrix combinations;  - an aluminum mirror; Y  - a glass window that closes the cavity, arranged parallel to the mirror, when pumping over solid dye-matrix combinations is transverse. 7. Laser radiation system according to any one of claims 1 to 5, comprising a dispersive cavity which in turn comprises:  - a pair of cylindrical lenses to focus the excitation-selectively pumping beam on one of the dye and solid matrix combinations;  - an aluminum mirror, arranged parallel to the faces of the sample, and perpendicular to the axis of the cavity defined by the perpendicular to the flat faces of the sample;  - a diffraction net, preferably holographic, arranged so that the sample with the dye is located between the rear mirror and the diffraction net, which forms an angle between 87 ° and 89 ° with the axis of the cavity; Y - an aluminum mirror, called a tuning mirror, which is arranged perpendicular to the direction defined by order 1 of the diffraction network, when pumping over solid dye-matrix combinations is transverse. 8. Laser radiation system according to any one of claims 1 to 5, comprising a dispersive cavity which in turn comprises:  - a pair of cylindrical lenses to focus the excitation-selectively pumping beam on one of the dye and solid matrix combinations;  - a dichroic mirror, partially transparent to the radiation emitted by the solid matrix dye, arranged parallel to the faces of the sample, and perpendicular to the axis of the cavity defined by perpendicular to the flat faces of the sample;  - a diffraction network, preferably holographic, located so that the sample with the dye is located between the dichroic mirror and the diffraction network, which forms an angle between 87 ° and 89 ° with the axis of the cavity; Y  - an aluminum mirror, called a tuning mirror, which is arranged perpendicular to the direction defined by order 1 of the diffraction network, when pumping over solid dye-matrix combinations is transverse. 9. Laser radiation system according to any one of claims 1 to 5, comprising a dispersive cavity which in turn comprises:  - a pair of cylindrical lenses to focus the excitation-selectively pumping beam on one of the dye and solid matrix combinations; - a dichroic mirror, partially transparent to the radiation emitted by the solid matrix dye, arranged parallel to the faces of the sample, and perpendicular to the axis of the cavity defined by the perpendicular to the flat faces of the sample;  - one or two prisms located so that the sample with the dye is located between the dichroic mirror and the prisms, which are arranged so that they act as expanders of the laser beam; Y - a diffraction network, preferably holographic, placed after the prisms in Littrow assembly, that is, placed so that, in the first order, it retro-reflects the radiation incident therein, when pumping over solid dye-matrix combinations is transverse. 6. Laser radiation system according to any one of claims 1 to 5, wherein the cavity further comprises:  - a spherical lens to focus the excitation-pumping beam selectively on one of the dye and solid matrix combinations; Y  - two dichroic mirrors, when the pumping over the solid dye-matrix combinations is longitudinal. 7. Laser radiation system according to any one of claims 1 to 6, wherein the wavelength tuner mechanism is a solid-dye matrix sample exchanger comprising a support located within the cavity, shaped like a disk or cylinder rotating, which is crossed by a rod in its geometric center, and houses around said central axis of the disc or cylinder solid-matrix dye combinations, as a revolver or ferris wheel. 8. Active medium for the generation and emission of laser light in a laser radiation system described in any one of claims 1 to 7, wherein said medium comprises at least one dye included in a solid matrix of at least one polymer. 9. Active medium according to claim 8, wherein the polymers comprising the solid matrix are selected from linear and crosslinked synthetic polymers. 10. Active medium according to any one of claims 8 or 9, wherein the polymers are selected from those obtained from the monomers of the group comprising: methyl methacrylate, 2-hydroxyethyl methacrylate, pentaerythritol tetracrilate, trifluoromethyl methacrylate , pentaerythritol triacrylate, 2-hydroxyethyl acrylate, triethoxymethyl-silyl propyl methacrylate, silylated monomers with silsesquioxane groups and combinations thereof. 11. Active medium according to claim 10, wherein the solid matrix has a composition selected from: methyl polymethacrylate; copolymer of hydroxyethyl methacrylate with methyl methacrylate, crosslinked with pentaerythritol tetracrylate; copolymer of methyl methacrylate with trifluoromethyl methacrylate; copolymer of methyl methacrylate with pentaerythritol triacrylate; 2-hydroxyethyl polymethacrylate; hydroxyethyl methacrylate copolymer with triethoxymethyl silyl propyl methacrylate; monomer copolymers of the selected group according to claim 10 with octa (methyl methacrylate) -silsesquioxane, and monomer copolymers of the selected group according to claim 10 with other silsesquioxane monomers. 12. Active medium according to any one of claims 8 to 1, wherein the dye belongs to the family of pyrometenes, rhodamines, perylenes, LDS, or any other dye emitted in the green-red region of the spectrum, or a combination from them. 13. Active medium according to any one of claims 8 to 12 wherein, for transverse pumping, the solid matrix is a 1 cm cylinder. of height and a diameter of between 4 and 10 mm., with a flat side face, parallel to its axis, between 1 to 6 mm. and polished until optical quality is obtained. 14. Active medium according to any one of claims 8 to 12 wherein, for longitudinal pumping, each of the selected combinations has the configuration of a disc of thickness greater than 1 mm. and of variable diameter.