WO2008054363A2

WO2008054363A2 - Organic thin film laser with tuneable bragg reflector

Info

Publication number: WO2008054363A2
Application number: PCT/US2006/034204
Authority: WO
Inventors: Justin R. Lawrence; Stephen H. Foulger
Original assignee: Clemson University
Current assignee: Clemson University
Priority date: 2005-09-01
Filing date: 2006-08-31
Publication date: 2008-05-08
Anticipated expiration: 2008-03-01
Also published as: WO2008054363A3

Abstract

A thin film laser is provided in which a peak wavelength of the thin film laser can be film laser dynamically tuned by applying a colloidal array reflector on a gain material, such as material doped with a laser dye. The dye-doped gain material is disposed on an optically reflective substrate to form the thin film laser. An excitation source optically pumps a laser light at the thin film laser, and the laser light is reflected by the optically reflective substrate. The laser light reverses direction and provides optical feedback to achieve lasing of the dye.

Description

TITLE OF THE INVENTION

ORGANIC THIN FILM LASER WITH TUNEABLE BRAGG REFLECTOR

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The Defense Advanced Research Projects Agency via the Space and Naval Warfare Systems Command sponsored research described herein under grant number N66001 -04-1 -8933.

BACKGROUND OF THE INVENTION

Lasers require two main elements for operation, an active material to provide optical gain and a resonator structure to provide optical feedback. There are a number of methods used to provide feedback in organic lasers such as distributed feedback gratings or a plane-parallel resonator. In the latter case, an organic gain material is deposited onto a dielectric mirror and capped with either a second dielectric mirror or an evaporated metal mirror to form a cavity. The light generated in the active material is Bragg reflected between the two dielectric mirrors. If the reflectivity of the mirrors is sufficiently high and the active material has adequate optical gain then the structure will begin to lase.

A laser dye normally is infiltrated into an inverse opal structure and can exhibit either random or distributed feedback lasing. Mechanically tunable lasers have been fabricated by using an elastomeric substrate with a Distributed Feedback (DFB) grating. Stretching the substrate changes the period of the grating and therefore the lasing wavelength. Similar work has been carried out with cholesteric liquid crystal elastomers.

Three-dimensional periodic dielectric structures are known to exhibit a photonic bandgap (PBG), and considerable attention has been given to developing these materials into a form suitable for use in photonic related applications. Unfortunately, the general exploitation of visible photonic crystals as devices has been hindered by the difficulties in 1) creating three-dimensional (3D) periodic dielectric structures with a feature size comparable to the wavelength of visible light and 2) achieving dielectric contrasts that result in a forbidden gap that overlaps in all directions within the Brillouin zone. One approach to address these challenges has focused on systems, which undergo self-organization at a nano-meter length scale, such as colloidal crystals. Systems exhibiting self-assembly characteristics hold promise as a practical route to generating optical photonic crystals, possibly with a complete PBG.

Colloidal crystal research of colloidal forces and self-assembly is leading to precursors for advanced materials. One class of materials that benefits from colloidal crystal research includes dimensionally periodic dielectric structures, which exhibit PBG.

There is widespread interest in coupling a dimensionally periodic dielectric structure with fluorescing molecules or polymers; thus, crystalline colloidal arrays (CCA) have been used to provide feedback for lasing. Using a CCA as an external reflector has a number of advantages. It eliminates the need for lithography to form the feedback and structure. It also removes the need for adding liquid crystals to or directly patterning the active medium. This makes this CCA reflector very versatile, compatible with many types of substrates and gain materials.

A CCA is a three-dimensionally ordered lattice of self-assembled monodisperse colloidal particles, most commonly amorphous silica or polymer latex, dispersed in aqueous or non-aqueous media. At high particle concentrations, long-range electrostatic interactions between particles result in a significant inter-particle repulsion, which yields the adoption of a minimum energy colloidal crystal structure with either body, centered cubic (bcc) or face- centered cubic (fee) symmetry. The ordering of the particles in the media results in spatial periodicities of the dielectric function that can result in both allowed and forbidden directions for electromagnetic waves of certain wavelengths to propagate. In the case of the CCAs, the ordering results in spatial periodicities that range from, for example, around 102-103 nm resulting in the appearance of optical bandgap effects. The skilled artisan will recognize that the distance between the particles can be varied over a much wider range and still show Bragg reflection at optical wavelengths. Unfortunately, the low elastic modulus (10^"2-10^~3 Pa) exhibited by a liquid dispersion results in weak shear, gravitational, electric field, or thermal forces having the propensity to disturb the crystalline order and is a severe drawback to the practical application of CCAs in photonic devices. For instance, a liquid phase CCA will undergo a disordering when subjected to a mechanical shock, after which, the system will again self-assemble, while a permanent disordering can be induced to incur with the introduction of ionic impurities. Recently, approaches to develop robust network matrixes have been pioneered to stabilize both organic and inorganic arrays through an in situ polymerization of a monomer around the ordered arrays. Specifically, colloidal crystals composed of polymeric arrays have been stabilized through encapsulation in hydrogel networks and have been referred to as a polymerized crystalline colloidal arrays (PCCAs). The PCCA films contain at least 30 vol.-% water, resulting in their fragility and propensity for significant changes in optical performance with water content.

A dynamically tuneable laser is needed in industry, which places an organic polymer between a dielectric mirror and a tuneable reflector to provide dynamic tuning of peak lasing wavelength.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed in general to a thin film laser that that can be tuned in real time for spectroscopic or interferometric analyses or used in other optics applications. The thin film laser is fabricated, for instance, by spin coating a thin layer of organic dye doped gain material onto a dielectric mirror and applying a polymeric crystalline colloidal array onto the gain material to form a composite mirror. Light is optically pumped through the composite mirror, for instance, to take spectroscopic or interferometric measurements. The composite mirror can be at least partially disassembled by removing the polymeric crystalline colloidal array and applying an alternative array in order to utilize the restructured composite mirror in a different fashion without having to build or provide a separate laser cavity for disparate uses. Two forms of manipulating monodisperse spherical colloidal particles for the generation of photonic crystals have emerged. One approach involves the assembly of the particles into close-packed arrays through sedimentation and typically relies on non-specific particle-particle "hard sphere" packing to induce order. Particle assembly via this method is attractive in terms of both simplicity and versatility. The second approach utilizes the long-range electrostatic repulsive interactions of charged colloidal spheres suspended in a liquid medium to procure order. These systems will often adopt a fragile crystal structure with either bcc or fee symmetry, though approaches to stabilize both inorganic and organic electrostatically stabilized arrays through an in situ polymerization of a monomer around the ordered arrays have been pioneered. These materials have been observed to exhibit a mechanochromic response, where the response has been attributed to an affine deformation of the lattice. The present invention harnesses this mechanochromic effect to control the lasing wavelength of a thin film organic laser.

In one aspect of the invention, a method for dynamically tuning a peak wavelength of a thin film laser includes the steps of applying a colloidal array reflector on a gain material doped with a laser dye, the dye-doped gain material disposed on an optically reflective substrate to form a thin film laser; optically pumping a laser light in a direction of the thin film laser from an excitation source; and reflecting the laser light by the optically reflective substrate such that the laser light reverses direction; and providing optical feedback by the reflected laser light to achieve lasing of the dye. According to this exemplary method, the colloidal array reflector is made of a plurality of particles suspended in a polymer suspension. Each of the particles is dimensioned between about 1 nm to about 1000 nm. Also according to this method, the polymer suspension is polymerized methacrylate polyethylene glycol, 2-methoxyethyl acrylate, ethylene glycol dimethacrylate, and 2,2-diethoxyacetophenone to stabilize the colloidal crystals relative to each other. The polymer suspension is also protects the particles from ionic contamination. Further according to this method, the gain material is a polymeric material and a dye. For instance, the polymeric material can be a polymethylmethacrylate material, and the dye can be Rhodamine-B. Other exemplary gain media include polymers doped with laser dyes, conjugated polymers, polymers doped with nanocystals, and inorganic semiconductors such as gallium arsenide.

Also in this method, the optically reflective substrate can be a dielectric mirror. The excitation source is an amplified, pulsed dye laser for emitting the pump beam at a wavelength absorbable by a dye. An additional step according to the method is to direct the laser light through the colloidal array reflector to a fiber adapter, which communicates the emission characteristic of the dye to a spectrometer.

A lasing wavelength from the excitation source includes a peak wavelength shift of about 50 nm, and the peak wavelength is about 610nm. Another step includes mechanically inducing a peak wavelength shift by pressurizing the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered. The colloidal array reflector can be pressurized by pressing a rigid device against the colloidal array reflector.

According to the method, the peak wavelength shift can be induced by applying a current to the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered. Alternatively, the peak wavelength shift can be induced by heating the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered. By way of further alternative, the peak wavelength shift can be induced by injecting a gas in the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered.

Additional steps according to the method include removing the colloidal array reflector from the dye-doped gain material, replacing the colloidal array reflector with an altered colloidal array reflector to affect the emission characteristic of the dye, and coating a plurality of particles with a photoluminescent dye and suspending the coated particles in a polymer suspension to form the colloidal array reflector to effect mechanochromic tuning to modify an emission spectra from the colloidal array reflector.

According to another aspect of the invention, a thin film laser having a dynamically tuneable peak lasing wavelength includes a colloidal array reflector including a plurality of particles suspended in a polymer suspension; a dye- doped gain material; and an optically reflective substrate, the dye-doped gain material disposed between the colloidal array reflector and the optically reflective substrate to form a laser cavity, the laser cavity being configured to tune an emission characteristic of the laser dye.

Each of the particles in this aspect of the invention is generally circular in cross-section, each particle exhibiting a diameter of between about 1 nm to about 1000 nm. The gain material includes a polymeric material. The polymer suspension includes a polymerized methacrylate polyethylene glycol, 2- methoxyethyl acrylate, ethylene glycol dimethacrylate, and 2,2- diethoxyacetophenone being configured to stabilize the colloidal crystals relative to each other. The optically reflective substrate is a dielectric mirror. Also in this aspect, the pump source pumps a pump beam in a direction of the colloidal array reflector. The pump source can be an amplified dye laser being configured to emit the pump beam at a wavelength absorbable by the laser dye. A fiber pick-up device can be provided to communicate the emission characteristic of the laser dye to a computer for analysis. In yet another aspect of the invention, a thin film laser having a dynamically tuneable peak lasing wavelength includes a colloidal array reflector including a plurality of particles suspended in a polymer suspension; a gain material; and an optically reflective substrate. The gain material is located between the colloidal array reflector and the optically reflective substrate to form a laser cavity. The laser cavity is used to tune an emission characteristic of the gain material. In this aspect of the invention, the gain material can be a polymeric material. More particularly, the gain material can be a polymer doped with a laser dye, a conjugated polymer, a polymer doped with a plurality of nanocystals, an inorganic semiconductor such as gallium arsenide, or combinations of these materials.

Other aspects and advantages of the invention will apparent from the following description and the attached drawings, or can be learned through practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and advantages of the present invention are apparent from the detailed description below in combination with the drawings, in which:

FIGURE 1 is a perspective view of a laser system employing a thin film laser composite device in accordance with an aspect of the invention;

FIGURE 2 is a perspective view of the thin film laser composite device as employed in FIGURE 1 ; FIGURE 3 is shows a method of generating a crystalline colloidal array composite as used in the thin film laser composite device of FIGURE 2;

FIGURE 4 is how steps in a method according to one aspect of the invention in which a thin film laser composite device is shown schematically under stress; FIGURE 5 is a graph showing a transmission spectra of the thin film laser composite device as in FIG. 4;

FIGURE 6A is a fluorescence spectrum of the thin film laser composite device as in FIGURE 4;

FIGURE 6B is another fluorescence spectrum of the thin film laser composite device as in FIGURE 4;

FIGURE 6C is a graph showing output intensity of the thin film laser composite device as in FIGURE 4; FIGURE 7A is a graph showing a shift of lasing peak of the thin film laser composite device as in FIGURE 4 under increasing compression; and

FIGURE 7B is a graph showing lasing wavelength variation of the thin film laser composite device as in FIGURE 4.

DETAILED DESCRIPTION OF THE INVENTION Detailed reference will now be made to the drawings in which examples embodying the present invention are shown. The detailed description uses numerical and letter designations to refer to features of the drawings. Like or similar designations of the drawings and description have been used to refer to like or similar parts of the invention.

The drawings and detailed description provide a full and detailed written description of the invention and of the manner and process of making and using it, so as to enable one skilled in the pertinent art to make and use it, as well as the best mode of carrying out the invention. However, the examples set forth in the drawings and detailed description are provided by way of explanation of the invention and are not meant as limitations of the invention. The present invention thus includes any modifications and variations of the following examples as come within the scope of the appended claims and their equivalents.

As broadly embodied in the figures, an optically pumped thin film laser system includes a dynamically tuneable photonic bandgap (PBG) composite mirror used to tune reflectance spectra, which can be useful in a variety of optical sensor and switching applications. In general, the composite mirror includes a dye-doped layer interposed between a dielectric mirror and a crystalline colloidal array (CCA) composite, which form a laser cavity. The dye- doped layer can be made of a polymer or a material with similar material properties and characteristics. The CCA composite includes a plurality of colloid particles, more particularly, spheres, which are relatively positioned and protected from contaminates by a suspension medium such as a polymeric material. With particular reference to FIGURE 1 , a thin film laser system is designated in general by the element number 10. The thin film laser system 10 broadly includes an optical pump or excitation source 12, a dynamically tuneable PBG composite mirror 14, a fiber optic spectrometer 16, and a computer display 18. As light from the excitation source 12 is pumped in a direction of the composite mirror 14, a wavelength of the laser spectra is dynamically tuneable by the composite mirror 14. The foregoing and other aspects and components of the thin film laser system 10 are described in greater detail and by example operation below. FIGURE 2 most clearly shows the composite mirror 14. In this example, the composite mirror 14 includes a crystalline colloidal array (CCA) composite 20 in the form of a film attached to a dye-doped polymer layer 22. The dye-doped polymer layer 22 is spin coated on a metal based or dielectric mirror 24, which upon optical excitation, produce a laser output, discussed below. The skilled artisan will recognize that the organic thin film can alternatively be sputtered on the metal and will further appreciate that some types of organic materials can be deposited by thermal evaporation. Those skilled in the art will further appreciate that the layer 22 can be formed of polymers doped with various laser dyes, conjugated polymers, polymers doped with nanocystals and inorganic semiconductors such as gallium arsenide, as well as various combinations of these materials; thus, the layer 22 is not limited to the exemplary dye-doped polymer.

Turning to FIGURE 3, the CCA composite 20 is a three-dimensionally ordered lattice of self-assembled monodisperse colloidal particles 26, which are generally spherically shaped in this example and made of amorphous silica, polymer latex, or a thermoplastic polymer such as polystyrene. As shown, a fully crosslinked polymer suspension or media 28 such as an acrylate polymer surrounds the CCA composite 20 in this aspect of the invention. The CCA composite 20 is a highly durable and water-free composite, which provides desired optical qualities of known hydrogel based polymerized crystalline colloidal arrays (PCCAs) films; however, the CCA composite 20 does not suffer from drawbacks inherent to PCCA films. For instance, PCCA films contain at least 30 vol.-% water, which results in their fragility and propensity for significant changes in optical performance with water content. The CCA composite 20 on the other hand is a mechanically robust composite film, which exhibits band stop tuning with mechanical stress but return to the optical characteristics of their unloaded state after cessation of stress. Additionally, the CCA composite 20 can be tailored such that its mechanical characteristics can be modified to suit an end-use criteria; therefore, the CCA composite 20 can be used as optical rejection filters, switches, limiters, and sensors

FIGURE 4 presents a schematic implementation of the tunable organic thin film laser 140 incorporating a crystalline colloidal array. More specifically, the gain medium 122 consists of a thin film of poly(methylmethacrylate) doped with Rhodamine B that has been spin coated onto a commercial dielectric mirror 124. The mirror 124 exhibits a broadband reflectivity of greater than 95 % across the entire emission spectrum of the dye. A second reflector, in the form of photonic bandgap composite 120 is laminated on top of the gain medium 122.

To better understand various aspects of the invention as discussed in the remaining figures, reference to a testing set-up follows. Materials selection and preparation

Monodisperse crosslinked polystyrene particles were prepared using an emulsion polymerization procedure described elsewhere. The resulting particles were dialyzed against deionized water and then shaken with an excess of mixed bed ion-exchange resin. After the cleaning procedures, the particle diameter was measured to be 150± nm with a Coulter N4Plus dynamic light scatter (DLS). Conductometric tritration indicated the charge density per particles was 1.36 uC/cm². The cleaned suspension was then diluted with deionized water until an angle dependent iridescence was observed.

The self-assembling particles were employed to synthesize polymerized crystalline colloidal arrays using procedures described with respect to FIGURE 5 below. Briefly, the typical procedure involved the stabilization of a crystalline colloidal array composed of monodisperse crosslinked polystyrene spheres dispersed in water through the encapsulation of the arrays with a photoinitiated free radical polymerized methacrylate functionalized poly(ethylene glycol) (PEG). Upon hydrogel encapsulation, the long-range order of the particles is stable to ionic contamination and minor mechanical deformation. Rhodamine B 1.5 (g/l) and polymethylmethacrylate (50 g/l) were dissolved in chloroform and spin coated onto a dielectric mirror (CVI Laser HN-0737-0) at 2000 rpm to give films of 1 μm thickness.

All chemicals were purchased from either Sigma-Aldrich of St. Louis, Missouri, or Acros Organics located in Geel, Belgium, although other comparable suppliers of biochemical and organic chemical products are available.

Optical Characterization

Fluorescence and lasing spectra were measured using a fiber-coupled grating spectrometer such as a Jobin Yvon Triax 190 available from HORIBA Jobin Yvon Inc., Edison, New Jersey; the spectrometer was equipped with a CCD detector. All data was collected at a temperature of 23 ⁰C unless otherwise noted. The dye was excited at 500 nm with 0.5 ns pulses at 6 Hz from a nitrogen laser pumped dye laser such as a Photonics Technology International GL 3300 / GL 302, available from Photon Technology International, Inc., Birmingham, New Jersey. The excitation beam was focused down to a spot diameter of 75 μm.

Turning now to Figure 5, a transmission spectrum of the thin film photonic bandgap composite 120 (e.g., including 80 μm thick photonic bandgap film) indicates a stop band that will reject about 30 % of the incident energy at a specific rejection wavelength and with a full width at half maximum (FWHM) of ca. 20-30 nm. Since the spectral distribution of the generated laser light is determined both by the luminescent lineshape of the gain medium and by the resonator modes, the "notch-like" reflectivity characteristics of the photonic bandgap composite will result in specific lasing wavelengths. By modifying the observed stop band, the lasing wavelength can also be altered. In order for a mechanochromically tuneable composite 120 to be used in a laser cavity, it must be capable of reflecting light emission from the gain material 122 back along the same path. To demonstrate this a dyed-doped polymer film was spin-coated onto a glass substrate and a composite film 120 was laminated on top. This allowed the effect of the composite on light emission from the gain medium to be examined free of any influence from the dielectric mirror. Measurements were made of light emission and reflection from the same area of the sample. A bifurcated optical fiber was used, with the output arm attached to the spectrometer and the input arm attached to a white light source (compare FIGURE 1 ). This allowed the fiber to be aligned so that the reflection spectrum could be measured from the same area of sample being excited for fluorescence without having to reset the experiment.

The reflection spectrum of the colloidal array composite 140 was measured normal to the plane of the film as shown in Figure 5. The reflection peak at 620 nm is due to Bragg scattering from the planes of the ordered array. The fluorescence spectrum of the PMMA/RhB film was also measured normal to the laminated composite (cf. left-most line in Figure 5). A pronounced "dip" in photoluminescence is observed at 616 nm and is due to light emission normal to the film being Bragg scattered back along its own path and is therefore unable to reach the detector. This is confirmed by the fact that the reflection peak coincides with the stop gap in emission to within 4 nm.

With reference now to Figures 6A-C, to examine the effects of the combined dielectric mirror / tuneable composite cavity 140 on the Rhodamine B emission, a sample was fabricated as outlined previously (see foregoing discussion regarding Figures 3 and 4). As shown in Figure 6A, the fluorescence spectrum below threshold was measured normal to the plane of the film, and a characteristic "dip" due to Bragg scattering from crystalline colloidal array appears. More specifically, a pronounced stop gap in photoluminescence is observed at 620 nm, similar to that seen in Figure 5. This indicates that light emitted at this wavelength is being Bragg scattered back through the gain material in the direction of the dielectric mirror thereby completing the laser cavity. As shown in Figure 6B, fluorescence spectrum of organic laser structure just above threshold shows lasing peak occurring at a wavelength Bragg scattered by the crystalline colloidal array. As the excitation intensity is increased above threshold, a sharp peak appears in the photoluminescence stop gap at 613 nm. The lasing peak is occurs at a slightly lower wavelength than the stop gap as this point has the optimum combination of reflectivity and gain. At higher intensities the sharp peak increases to dominate the spectrum (not presented). Measuring the output energy of the laser as a function of excitation energy reveals threshold type behavior with a threshold pump energy value of 3.5 μJ as shown in Figure 6C.

As discussed above, CCAs can exhibit a mechanochromic compression. With reference now to Figures 7A and 7B, this effect can be harnessed to tune the lasing wavelength. An organic thin film laser was fabricated as above but using a crystalline colloidal array composite with a reflection peak wavelength of 630 nm. The composite was placed under mechanical pressure (see, e.g., FIGURE 4) and the lasing spectrum was recorded as the compression was increased. As shown in Figure 7A, the lasing peak shifted to a shorter wavelength as a function of increasing compression on crystalline colloidal array. As shown, the unstrained composite showed a sharp peak at 632 nm. As shown in Figures 7A and 7B variation in observed lasing wavelength with compressive strain, as increasing strain was placed on the composite, the lasing peak shifted to shorter wavelengths. Two examples are shown in Figure 7A at 620 nm and 600 nm. When the pressure on the composite is released, the lasing peak shifts to longer wavelengths, returning to its original position. The tuning range in this case is 32 nm. This response is caused by an affine deformation of the PCCA lattice where the shift of the reflection stop band (and therefore lasing) to shorter wavelengths is due to the decrease in interplanar distance. This effect can be modeled from the following Bragg equation:

Λ_o = 2nd_m ύnθ where Λ₀ \s the wavelength of the stop gap, αf_ήWis the interplanar spacing, n is the refractive index of the PCCA (1.473) and θ is the Bragg angle. A number of devices were tested and the initial and final wavelengths obtained by tuning were recorded.

Using the Bragg equation given above, the interplanar spacing _din was calculated for these lasing peaks. From these values d/do, the ratio of compressed sample height to initial sample height and the strain can be found. Figure 4b shows the lasing wavelength shift as a function of strain. It can be seen that the 32 nm shift in lasing peak is caused by a compression of 5.1 %, which corresponds to a reduction of dm from 215 nm to 201 nm. Smaller compressions cause smaller changes in lasing wavelength on a linear scale. The wide tuning range of the colloidal array composite is due to the relatively large spacing between the electrostatically assembled particles when compared to sterically close packed spheres allows sufficient volume for compression of lattice without major disruption of the long range order.

The exploitation of mechanochromic tuning to shift the lasing wavelength of an organic laser incorporating a crystalline colloidal array composite has been demonstrated. A compression of 5.1 % is sufficient to shift the lasing wavelength across 32 nm. This response is directly linked to the large inter-particle spacings in colloidal arrays based electrostatically self-assembled polystyrene particles. The demonstration of tunability in a lasing structure makes these materials appealing for photonics applications.

While preferred embodiments of the invention have been shown and described, those skilled in the art will recognize that other changes and modifications may be made to the foregoing examples without departing from the scope and spirit of the invention. It is intended to claim all such changes and modifications as fall within the scope of the appended claims and their equivalents.

Claims

1. A method for dynamically tuning a peak wavelength of a thin film laser, the method comprising the steps of. (a) applying a colloidal array reflector on a gain material doped with a laser dye, the dye-doped gain material disposed on an optically reflective substrate to form a thin film laser;

(b) optically pumping a laser light in a direction of the thin film laser from an excitation source; and (c) reflecting the laser light by the optically reflective substrate such that the laser light reverses direction; and

(d) providing optical feedback by the reflected laser light to achieve lasing of the dye.

2. The method as in Claim 1 , wherein the colloidal array reflector is made of a plurality of particles suspended in a polymer suspension.

3. The method as in Claim 2, wherein each of the particles is dimensioned between about 1 nm to about 1000 nm.

4. The method as in Claim 2, wherein the polymer suspension is polymerized methacrylate polyethylene glycol, 2-methoxyethyl acrylate, ethylene glycol dimethacrylate, and 2,2-diethoxyacetophenone being configured to stabilize the colloidal crystals relative to each other.

5. The method as in Claim 2, wherein the polymer suspension is configured to protect the particles from ionic contamination.

6. The method as in Claimi , wherein the gain material is a polymeric material and a dye.

7. The method as in Claim 6, wherein the polymeric material is a polymethylmethacrylate material.

8. The method as in Claim 6, wherein the dye is Rhodamine-B.

9. The method as in Claim 1 , wherein the optically reflective substrate is a dielectric mirror.

10. The method as in Claim 1 , wherein the excitation source is an amplified dye laser being configured to emit the pump beam at a wavelength absorbable by a dye.

11. The method as in Claim 1 , wherein the excitation source is a pulsed laser.

12. The method as in Claim 1 , further comprising the step of directing the laser light through the colloidal array reflector to a fiber adapter, the fiber adapter being configured to communicate the emission characteristic of the dye to a spectrometer.

13. The method as in Claim 1 , wherein a lasing wavelength from the excitation source includes a peak wavelength shift of about 50 nm.

14. The method as in Claim 1 , wherein a peak wavelength is about 610nm.

15. The method as in Claim 1, further comprising the step of mechanically inducing a peak wavelength shift by pressurizing the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered.

16. The method as in Claim 15, wherein the colloidal array reflector is pressurized by pressing a rigid device against the colloidal array reflector.

17. The method as in Claim 1 , further comprising the step of inducing a peak wavelength shift by applying a current to the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered.

18. The method as in Claim 1 , further comprising the step of inducing a peak wavelength shift by heating the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered.

19. The method as in Claim 1 , further comprising the step of inducing a peak wavelength shift by injecting a gas in the colloidal array reflector to alter an interplanar distance between at least two particles disposed in the colloidal array reflector, the emission characteristic being a wavelength of a photoluminescence spectrum, the wavelength being tuned as the interplanar distance is altered.

20. The method as in Claim 1 , further comprising the steps of removing the colloidal array reflector from the dye-doped gain material and replacing the colloidal array reflector with an altered colloidal array reflector to affect the emission characteristic of the dye.

21. The method as in Claim 1 , further comprising the steps of coating a plurality of particles with a photoluminescent dye and suspending the coated particles in a polymer suspension to form the colloidal array reflector to effect mechanochromic tuning to modify an emission spectra from the colloidal array reflector.

22. A thin film laser having a dynamically tuneable peak lasing wavelength, the thin film laser comprising: a colloidal array reflector including a plurality of particles suspended in a polymer suspension; a gain material doped with a laser dye; and an optically reflective substrate, the dye-doped gain material disposed between the colloidal array reflector and the optically reflective substrate to form a laser cavity, the laser cavity being configured to tune an emission characteristic of the laser dye.

23. The thin film laser as in Claim 22, wherein each of the particles is substantially circular in cross-section, each particle exhibiting a diameter of between about 1 nm to about 1000 nm.

24. The thin film laser as in Claim 22, wherein the gain material includes a polymeric material.

25. The thin film laser as in Claim 22, wherein the polymer suspension includes a polymerized methacrylate polyethylene glycol, 2-methoxyethyl acrylate, ethylene glycol dimethacrylate, and 2,2-diethoxyacetophenone being configured to stabilize the colloidal crystals relative to each other.

26. The thin film laser as in Claim 22, wherein the optically reflective substrate is a dielectric mirror.

27. The thin film laser as in Claim 22, further comprising a pump source being configured to pump a pump beam in a direction of the colloidal array reflector.

28. The thin film laser as in Claim 27, wherein the pump source is an amplified dye laser being configured to emit the pump beam at a wavelength absorbable by the laser dye.

29. The thin film laser as in Claim 27, further comprising a fiber pick-up device being configured to communicate the emission characteristic of the laser dye to a computer for analysis.

30. A thin film laser having a dynamically tuneable peak lasing wavelength, the thin film laser comprising: a colloidal array reflector including a plurality of particles suspended in a polymer suspension; a gain material; and an optically reflective substrate, the gain material disposed between the colloidal array reflector and the optically reflective substrate to form a laser cavity, the laser cavity being configured to tune an emission characteristic of the gain material.

31. The thin film laser as in Claim 30, wherein each of the particles is substantially circular in cross-section, each particle exhibiting a diameter of between about 1 nm to about 1000 nm.

32. The thin film laser as in Claim 30, wherein the gain material includes a polymeric material.

33. The thin film laser as in Claim 30, wherein the gain material is selected from the group consisting of a polymer doped with a laser dye, a conjugated polymer, a polymer doped with a plurality of nanocystals, an inorganic semiconductor and combinations thereof.

34. The thin film laser as in Claim 33, wherein the inorganic semiconductor is gallium arsenide.

35. The thin film laser as in Claim 30, wherein the polymer suspension is configured to stabilize the colloidal crystals relative to each other.

36. The thin film laser as in Claim 30, wherein the optically reflective substrate is a dielectric mirror.

37. The thin film laser as in Claim 30, further comprising a pump source being configured to pump a pump beam in a direction of the colloidal array reflector.

38. The thin film laser as in Claim 30, further comprising a fiber pick-up device being configured to communicate the emission characteristic of the gain material to a computer for analysis.