CN102832535A - Solid-state 698nm deep red laser device with blue laser light-emitting diode (LED) pump - Google Patents

Abstract

The invention relates to a laser device and provides a solid-state 698nm deep red laser device with a blue laser light-emitting diode (LED) pump. The laser device utilizes a direct down-conversion manner to obtain 698nm deep red laser, is compact in structure and high in conversion efficiency, and has very high application potential. One light path is sequentially provided with a semiconductor laser device, a collimation lens, a focusing lens, a plane input lens, a laser medium and a plane-concave output lens which are located on one optical axis, wherein the semiconductor laser device is a blue laser LED with the central wavelength of 444nm, and the laser medium is a praseodymium-doped lithium yttrium fluoride crystal; and a plane-concave stable cavity structure is formed by the plane input lens, the laser medium and the plane-concave output lens.

Description

Blue laser diode pumped 698nm deep red solid-state laser

technical field

The invention relates to a laser, in particular to a blue-light laser diode-pumped 698nm deep-red solid-state laser directly adopting a down-conversion mechanism.

Background technique

Deep red laser is widely used in laser display, optical storage, laser medical treatment, spectroscopy and other fields. Using deep red laser as the light source of laser display can obtain a larger display color gamut and make the display image more full and vivid. In particular, the narrow-linewidth deep red laser with a wavelength of 698nm can be used as a detection light source for strontium atomic clocks, which is of great significance for long-distance remote navigation and cosmological constant measurement.

However, currently, there are few reports on lasers working at 698nm. The technical methods to obtain lasers near this wavelength are mainly as follows:

1. Laser diodes that emit red light directly. At present, there are many laser diodes working at 660-670nm in commercial use, but there are no reports on diodes that directly radiate 698nm deep red laser. This type of laser controls the wavelength by controlling the composition of the semiconductor material (such as InGaAsP). The pump energy is provided by external current injection. The advantage is that it is easy to integrate. The disadvantage is that the output laser linewidth is wide and the beam quality is poor.

2. Utilizes tunable laser technology. These techniques take advantage of the broadband gain of laser materials, with sophisticated wavelength-selective devices to select the output at a certain wavelength. For example, Newport Company of the United States produced a broadband tunable continuous output laser 3900S based on titanium-doped sapphire, with a tuning range of 675-1100nm (see http://www.newport.com); Germany Toptica Company also produced semiconductor-based Broadband tunable laser DL100 (see http://www.toptica.com), its tuning range includes 632 ~ 1770nm. Among them, the former is pumped by flash lamp or green laser, and the latter is pumped by electric injection. The gain material used in this type of laser has broadband gain, and then the laser output of a certain wavelength is selected by a precise wavelength selection device (such as Littrow grating). Materials with broadband gain tend to have smaller gain cross-sectional areas and higher laser thresholds; the use of precision wavelength selective devices introduces insertion loss, which reduces the efficiency of the laser, and at the same time puts forward high requirements on the mechanical design of the laser, making the overall laser structure complex , the cost is high.

3. Using solid-state laser frequency doubling technology. This is the most commonly used technology to obtain red laser with high beam quality. According to literature search, there is still no solid-state laser frequency-doubled laser working at 698nm. The most typical technology of this type is to use a semiconductor laser working near 800nm to pump neodymium-doped gain media (such as Nd:YAG, Nd:YVO ₄ , Nd:YLF, Nd:GdVO _{4 ,} etc.), first to obtain a working near 1.3μm Infrared lasers, sometimes using tunable technology to fine-tune the infrared laser to the desired wavelength. Then use frequency doubling crystals (such as KTP, LBO, PPLN, etc.) to double the laser frequency to obtain red laser light. This type of laser is a red laser achieved by two steps of "infrared semiconductor laser pumping neodymium-doped medium to obtain infrared solid laser" + "infrared solid laser frequency doubling". The frequency doubling technology introduces a nonlinear process, not only for temperature, Environmental factors such as angles are very sensitive, and the extra frequency conversion greatly limits the improvement of laser efficiency; at the same time, the structure of the laser is complex and the cost is high.

K.Nejezchleb,andV.

“Visible cw laser emission GaN-diode pumped Pr:YAlO₃ crystal,”Appl.Phys.B 97,363-367(2009)；参考文献3：M.Fibrich,H.Jelínková,J.

K.Nejezchleb,and V.

“Pr:YAlO₃ micochip laser at 662nm,”Laser Phys.Lett.8,116-119(2011).）。然而，目前有关掺镨激光器的研究基本还停留在实验室阶段，且激光二极管泵浦的掺镨激光器实现的698nm红光激光器仍未见报道。汉堡大学激光物理研究所曾研制了此波长附近的染料激光器泵浦掺镨脉冲激光器（见参考文献4：T.Danger,T.Sandrock,E.Heumann,G.Huber,and B.Chai,“Pulsedlaser action of Pr:GdLiF₄ at room temperature,”Appl.Phys.B 57,239-241(1993).），并对其有性能报道。但其激光器只能输出一个个的脉冲，不能实现连续稳定输出；并且采用染料激光器或者氩离子激光器泵浦，直接导致激光器体积复杂，依赖复杂的水冷装置，稳定性差，效率低下，且染料激光器寿命较低。In addition to the above technologies, the use of praseodymium-doped gain media can obtain red lasers in direct down-conversion mode. At present, the red light output wavelengths of praseodymium-doped lasers pumped by laser diodes are only reported to be 640nm, 721nm, 747nm, and 662nm (see reference 1: F. Cornacchia, A. Di Lieto, M. Tonelli, A. Richter, E. Heumann, and G. Huber, "Efficient visible laser emission of GaN laser diode pumped Pr-doped fluoride sceelite crystals," Opt. Express 16, 15932-15941 (2007); Reference 2: M. Fibrich, H. Jelínková, J.

K. Nejezchleb, and V.

"Visible cw laser emission GaN-diode pumped Pr:YAlO ₃ crystal," Appl. Phys. B 97, 363-367 (2009); Reference 3: M. Fibrich, H. Jelínková, J.

K. Nejezchleb, and V.

"Pr:YAlO ₃ micochip laser at 662nm," Laser Phys. Lett.8, 116-119(2011).). However, the current research on praseodymium-doped lasers is basically still in the laboratory stage, and the 698nm red laser realized by laser diode-pumped praseodymium-doped lasers has not been reported yet. The Institute of Laser Physics of the University of Hamburg has developed a dye laser pumped praseodymium-doped pulsed laser near this wavelength (see reference 4: T.Danger, T.Sandrock, E.Heumann, G.Huber, and B.Chai, "Pulsedlaser action of Pr:GdLiF ₄ at room temperature,"Appl.Phys.B 57,239-241(1993).), and reports on its performance. However, its laser can only output pulses one by one, and cannot achieve continuous and stable output; and the use of dye lasers or argon ion lasers for pumping directly leads to complex volumes of lasers, relying on complex water cooling devices, poor stability, low efficiency, and lifespan of dye lasers lower.

Contents of the invention

The object of the present invention is to overcome the disadvantages of low efficiency, complex volume, high cost, and poor beam quality of current lasers with a wavelength near 698nm, and provide a blue-light laser diode-pumped 698nm deep-red solid-state laser. The 698nm deep red laser is obtained by conversion, which has a compact structure and high conversion efficiency, and has great application potential.

In the present invention, a semiconductor laser, a collimating lens, a focusing lens, a plane input mirror, a laser medium and a plano-concave output mirror are sequentially arranged on an optical path, and the semiconductor laser, a collimating lens, a focusing lens, a plane input mirror, a laser medium and a plano-concave output mirror are sequentially arranged. The output mirrors are located on the same optical axis, the semiconductor laser is a blue laser diode with a center wavelength of 444nm, and the laser medium is a praseodymium-doped yttrium lithium fluoride crystal (hereinafter referred to as Pr:YLF); the planar input mirror, laser medium and flat The concave output mirror constitutes a plano-concave stable cavity structure.

The pumping source pumps praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystal using a blue semiconductor laser, and the semiconductor laser is a blue laser diode with a center wavelength of 444nm; the plane input mirror is plated with a high transmittance of 444nm And 698nm high reflectance (R>99.5) dielectric film, the plano-concave output mirror is coated with 698nm partial transmission (T<5%) dielectric film, and the two dielectric films maintain sufficiently high transmittance at 640nm and 720nm .

The present invention adopts the direct down-conversion mechanism to obtain the red laser light without any frequency doubling device. Using a blue semiconductor laser as the pump source to pump praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystals, the praseodymium ions complete the transition from the ground state to the ³ P ₂ energy level, and then the praseodymium ions relax from ^{the 3} P ₂ energy level to ^{the 3} P ₀ energy level, and finally obtain 698nm deep red laser in the direct down-conversion transition from ³ P ₀ energy level → ³ F ₃ energy level.

Through the above-mentioned cavity film system design, the present invention realizes the 698nm deep red laser output pumped by the blue light diode for the first time in the Pr:YLF crystal. The field has important academic significance and application value. The outstanding effects of the present invention will be described in the specific implementation manner.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

FIG. 2 is a relationship curve between the output power of the blue laser diode pumped 698nm laser and the power of the absorbed pump laser according to an embodiment of the present invention. The transmittance corresponding to the plano-concave output mirror at 698nm is 0.5%.

FIG. 3 is a graph showing the relationship between the blue laser diode pumped 698nm laser output power and the absorbed pump laser power according to an embodiment of the present invention. The transmittance corresponding to the plano-concave output mirror at 698nm is 0.9%. The abscissa is the absorbed power (mW), and the ordinate is the output power (mW).

Fig. 4 is a spectrum diagram of the 698nm output laser according to the embodiment of the present invention. The spectral resolution is 0.14nm. The abscissa is the wavelength λ (nm), and the ordinate is the optical power (dBm).

Fig. 5 is a spectrum diagram of 698nm output laser according to the embodiment of the present invention. The spectral resolution is 0.01nm. The abscissa is the wavelength λ (nm), and the ordinate is the optical power (a.u).

Detailed ways

The invention includes three parts: pumping light collimation and focusing system, crystal design and resonant cavity design.

Fig. 1 is a schematic structural diagram of an embodiment of the present invention. As can be seen from Fig. 1, the blue-ray laser diode pumping 698nm red-light solid-state laser of the present invention is followed by a semiconductor laser 1, a collimating lens 2, a focusing lens 3, a plane input mirror 4, a laser medium 5, and a plano-concave output on an optical path. Mirror 6 composition. The semiconductor laser 1 is a blue laser diode with a center wavelength of 444nm, and the laser medium 5 adopts Pr:YLF crystal.

Due to the large divergence angle of the blue laser diode, a collimator lens must be used to collimate it so that it becomes a quasi-parallel light with a small divergence angle. Afterwards, the focusing lens converges the blue laser pump beam near the incident end face of the crystal. A plano-convex lens with a focal length of 50 mm is used as the focusing lens, and the pump spot radius formed in the laser medium is about 60 μm. Further improving the quality of the pump light spot can be achieved by adding a beam shaping device after the collimator lens.

In order to ensure that the blue pumping laser light is absorbed by the Pr:YLF crystal as much as possible, the crystal is placed in a direction parallel to the c-axis direction of the crystal and the polarization direction of the blue light diode output laser. Since the frequency doubling method is not used (that is, the frequency doubling crystal that is very sensitive to temperature is not used), and the current single-tube power of the blue laser diode does not exceed 1.6W, the laser crystal is placed in a copper common crystal seat, and no additional cooling or cooling is required. Temperature control device.

For the resonant cavity, choose a plano-concave stable cavity structure that is easy to adjust, easy to achieve mode matching, and has a large controllable mode volume. It is composed of a planar input mirror, a Pr:YLF crystal, and a plano-concave output mirror. The position of the crystal is close to the planar input mirror, and the distance from the planar input mirror to the plano-concave output mirror is close to the curvature radius of the plano-concave output mirror, in order to obtain low laser threshold and higher output power. The planar input mirror of the present invention is coated with a dielectric film with high transmittance of 444nm and high reflectivity of 698nm (R>99.5) as the input cavity mirror of the laser; the plano-concave output mirror is coated with a 698nm partial transmission (T<5%) The dielectric film is used as the output cavity mirror of the laser. Since the Pr:YLF laser is pumped by a blue laser diode, it has achieved laser lasing at two wavelengths of 640nm and 720nm in the red light band, among which the gain of the 640nm spectral line is the largest, the gain of the 720nm spectral line is the second, and the gain of the 698nm spectral line is the largest. The gain of the line is the smallest, and the wavelength is in the middle of two stronger gain spectral lines. In order to suppress these two recent spectral lines with stronger gain, the present invention adopts a special film system design, so that the transmittance of the input mirror and the output mirror is much larger at 640nm and 720nm than at 698nm, causing their lasers to The vibration threshold is larger than 698nm, so that in the spectral line competition, the 698nm spectral line is first lased to generate laser light, and the two stronger spectral lines of 640nm and 720nm are suppressed to generate lasing. Finally, a single-wavelength laser with a stable output of 698nm was obtained.

Figure 2 and Figure 3 are the relationship curves between the 698nm laser output power and the absorption pump laser power, where Figure 2 corresponds to the transmittance of the plano-concave output mirror at 698nm at 0.5%, and Figure 3 corresponds to the transmittance of the plano-concave output mirror at 698nm 0.9%. It can be seen from Figure 2 that when the transmittance of the output coupling mirror is 0.5%, the threshold value of the laser is 47mW, the slope efficiency is 26.9%, and the corresponding output power is 115mW when the absorbed pump laser power is about 500mW. The efficiency is 22.9%. It can be seen from Figure 3 that when the transmittance of the output coupling mirror is 0.9%, the threshold value of the laser is 139mW, the slope efficiency is 48.7%, and the corresponding output power is 156mW when the absorbed pump laser power is about 500mW. The efficiency is 31.0%.

Figure 4 shows the 698nm laser spectrum measured by a spectrum analyzer with a measurement resolution of 0.14nm. It can be seen that the laser only outputs the laser with the transition of the 698nm spectral line, while the nearby 640nm and 720nm spectral lines are well suppressed and there is no vibration. When the resolution of the spectrum analyzer is 0.01nm, the measured laser spectrum is shown in Figure 5. The visible laser spectrum consists of multiple peaks, which is the multi-longitudinal mode spectrum of the laser. The wavelength interval between adjacent peaks is measured to be 0.03nm, which is determined by the laser crystal parameters.

Claims (5)

1. Blue light laser diode pumping 698nm deep red solid laser, it is characterized in that semiconductor laser, collimating lens, focusing lens, plane input mirror, laser medium and plano-concave output mirror are arranged successively on an optical path, described semiconductor laser, The collimating lens, the focusing lens, the plane input mirror, the laser medium and the plano-concave output mirror are located on the same optical axis, the semiconductor laser is a blue laser diode with a center wavelength of 444nm, and the laser medium is a praseodymium-doped yttrium lithium fluoride crystal; The plano-concave stable cavity structure is formed by the planar input mirror, the laser medium and the plano-concave output mirror. 2. The blue-light laser diode-pumped 698nm deep-red solid-state laser according to claim 1, wherein the pumping source pumps the praseodymium-doped yttrium lithium fluoride crystal using a blue-light semiconductor laser. 3. The blue laser diode pumped 698nm deep red solid laser as claimed in claim 2, characterized in that said semiconductor laser is a blue laser diode with a central wavelength of 444nm. 4. blue light laser diode as claimed in claim 1 pumps 698nm crimson light solid-state laser device, it is characterized in that described planar input mirror is coated with 444nm high transmittance and 698nm dielectric film, the reflectivity R of described 698nm dielectric film >99.5. 5. The blue laser diode pumped 698nm deep red solid-state laser according to claim 1, characterized in that the plano-concave output mirror is coated with a 698nm dielectric film, and the partial transmittance T of the 698nm dielectric film is <5%.

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