All-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal

Abstract

The present invention provides a all-solid-state laser that directly emits 486.1 nm blue laser based on a praseodymium-doped fluoride crystal. The laser includes an excitation source, a focusing system, a laser resonator, and a laser gain medium crystal. The excitation source is a laser diode laser that emits laser with a central wavelength of 440 - 445 nm; the laser resonator is composed of an input mirror and an output mirror coated with a film system for realizing blue laser; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions. By using the Pr 3+ ion 3 P0→ 3 H4 energy level transition to directly emit 486.1 nm wavelength blue laser, the signal-to-noise ratio of the laser can be improved. The blue laser fabricated by the present invention has the advantages of simple and compact structure, high stability, good monochromaticity, small volume, low power consumption, etc. And by means of Q-switching, a high peak power blue laser pulse output can be obtained, which can meet the requirements of high power and high integration miniaturized blue lasers for ocean exploration and underwater communication.

Description

Technical Field

[0001] The present invention relates to laser crystal materials and lasers, in particular to a all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal. Background Art

[0002] Based on the optical transmission window of seawater (450 - 550 nm), miniaturized all-solid-state blue-green lasers have been widely used in marine exploration systems, including laser underwater communication, laser bathymetry, and laser detection radar, etc. Due to the differences in the spectral attenuation coefficients of different types of seawater, blue lasers in the 450 - 490 nm band are suitable for deep-sea exploration, and green lasers in the 520 - 550 nm band are more suitable for near-shore exploration. Through calculation, it can be known that the transmission distance of deep seawater at 490 nm can be increased by about 50% compared with that at 532 nm. Among them, 486.1 nm is the Fraunhofer dark line. Using this wavelength for transmission or communication can effectively avoid environmental noise and improve the signal-to-noise ratio. Therefore, using 486.1 nm blue laser to implement underwater high-speed communication and seabed detection has become the most potential technical means. The core of this technical means is a blue laser light source with a specific spectral linewidth, specific peak power, and high repetition frequency. Currently, the methods to achieve 486.1 nm blue laser mainly include: 1) Obtained by frequency doubling of a 972 nm semiconductor laser (CN1044193A). This method requires complex technologies such as feedback compression to improve the beam quality and compress the emission linewidth. 2) Obtained by quadruple frequency of thulium (Tm)-doped fiber (CN105703212A). This method has disadvantages such as complex structure design and low output power. 3) Obtained by sum frequency between wavelengths of neodymium (Nd)-doped crystal (CN109586153B). This method has a complex structure design and low conversion efficiency. 4) Obtained by combining optical parametric oscillation technology with frequency doubling and sum frequency (CN114006253A). This method involves multiple nonlinear effects and has disadvantages such as complex structure, low electro-optical conversion efficiency, high power consumption, and large volume. Therefore, there is an urgent need for a gain medium that directly emits 486.1 nm blue laser, which can directly obtain high-peak-power blue laser output through the Q-switching method without going through the nonlinear optical conversion process, especially 486.1 nm blue light, which can compress the volume of the laser, improve the efficiency, reduce the system power consumption, and promote the rapid development of a miniaturized low-power blue laser underwater communication system.

[0003] Pr 3+ Ion has rich energy levels. Most current research focuses on achieving red light (640 nm) and deep red light (720 nm) laser output because the emission cross-sections of these two wavelengths are relatively large and the gain is relatively high. From the perspective of the energy level structure, Pr 3+ ion 3 P0→ 3The H4 energy level transition can emit 486.1 nm blue laser light. However, the 486.1 nm laser is the emission peak of the zero phonon line, which is a quasi-three-level transition with strong reabsorption and is relatively difficult to achieve laser output. Through the study of the quasi-three-level transition mechanism and the crystal spectral properties, the present invention proposes to use Pr:LaF3 (Optics Express 20, 20387, 2012) and Pr:KY3F 10 crystal (Optics Express 21, 31274, 2013) and a suitable narrowband resonant cavity coating method to directly and efficiently output 486.1 nm blue laser light. The fabricated blue laser has the advantages of simple and compact structure, high stability, good monochromaticity, small volume, low power consumption, etc. Moreover, by means of Q-switching, a blue laser output with high peak power can be obtained, which has great application potential in underwater communication. In addition, by adjusting the parameters of the laser resonant cavity, dual-wavelength output of 486.1 nm and 520 nm blue-green lasers can be achieved for duplex laser communication, multi-user communication, and lidar detection. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a all-solid-state laser directly emitting 486.1 nm blue laser light based on a praseodymium-doped fluoride crystal, which utilizes the Pr 3+ ion 3 P0→ 3 H4 energy level transition and a narrowband resonant cavity coating method to directly achieve efficient 486.1 nm blue laser output. By adjusting the parameters of the resonant cavity, dual-wavelength output of 486.1 nm and 520 nm blue-green lasers is obtained. The fabricated laser has the advantages of simple and compact structure, good stability, high reliability, low power consumption, small volume, etc.

[0005] The technical solution of the present invention is as follows:

[0006] A all-solid-state laser directly emitting 486.1 nm blue laser light based on a praseodymium-doped fluoride crystal, which can directly output 486.1 nm blue laser light, is characterized in that it includes an excitation source, a focusing system, a laser resonant cavity, and a laser gain medium crystal;

[0007] The excitation source is a laser diode laser emitting laser light with a central wavelength of 440 - 445 nm;

[0008] The laser resonant cavity is composed of an input mirror and an output mirror; the input mirror is coated with a dielectric film that is highly transmissive to the 440 - 445 nm and 510 - 750 nm bands and highly reflective to the 475 - 495 nm band; the output mirror is coated with a dielectric film that is highly transmissive to the 510 - 750 nm band and partially transmissive to the 475 - 495 nm band;

[0009] The laser gain medium crystal is a praseodymium ion-doped fluoride crystal;

[0010] Along the laser output direction of the excitation source, a focusing system, an input mirror, a laser gain medium crystal, and an output mirror are arranged in sequence;

[0011] Preferably, the output mode of the excitation source is single-tube output or fiber-coupled output;

[0012] Preferably, when the excitation source is single-tube output, the focusing system includes one aspherical mirror for beam collimation, a pair of cylindrical lenses for shaping, and one convex lens for focusing; when the excitation source is fiber-coupled output, the focusing system consists of two convex lenses for collimating and focusing the pump light of the excitation source.

[0013] Preferably, the input mirror is formed by coating a dielectric film on the input mirror that has high transmittance for the 440 - 445 nm and 510 - 750 nm wavelength bands and high reflectance for the 475 - 495 nm wavelength band, and it is a plane mirror; the output mirror is formed by coating a dielectric film on the output mirror that has high transmittance for the 510 - 750 nm wavelength band and partial transmittance for the 475 - 495 nm wavelength band, and it is a plano-concave mirror with a curvature of 50 - 200 mm.

[0014] Preferably, the laser gain medium is praseodymium ion-doped lanthanum fluoride (LaF3) or potassium yttrium fluoride (KY3F 10 ) crystal, which can be obtained by existing technologies; the doping concentration of praseodymium ions is 0.05 at.% - 2 at.%, preferably 0.05 at.% - 1 at.%. The laser gain medium crystal is located near the focus of the focusing system, where the light spot is smaller and the light intensity density is larger, which is beneficial to the absorption of pump light and realizes population inversion.

[0015] Preferably, the light-passing surface of the laser medium crystal is circular, square, or rectangular. After the light-passing surface is polished, it is coated with an antireflection dielectric film or not coated with a dielectric film, and the length of the light-passing direction is 2 mm - 20 mm, preferably 3 mm - 10 mm.

[0016] According to the present invention, a preferred embodiment is:

[0017] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, comprising an excitation source, a focusing system, an input cavity mirror, a laser gain medium crystal, and an output cavity mirror arranged in sequence along the optical path direction; the excitation source is a laser diode laser emitting laser with a central wavelength of 440 - 445 nm, and the output mode is single-tube output; the focusing system consists of 1 aspherical mirror, a pair of cylindrical lenses, and 1 convex lens; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions; the input cavity mirror and the output cavity mirror form a laser resonator; the input cavity mirror is a plane mirror with a dielectric film on the input mirror that has high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band; the output cavity mirror is a plano-concave mirror with a curvature of 50 - 200 nm, and the output mirror has a dielectric film that has high transmittance for the 510 - 750 nm band and partial transmittance for the 475 - 495 nm band.

[0018] According to the present invention, another preferred embodiment is:

[0019] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, comprising an excitation source, a focusing system, an input cavity mirror, a laser gain medium crystal, and an output cavity mirror arranged in sequence along the optical path direction; the excitation source is a laser diode laser emitting laser with a central wavelength of 440 - 445 nm, and the output mode is single-tube output; the focusing system consists of 1 aspherical mirror, a pair of cylindrical lenses, and 1 convex lens; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions; the input cavity mirror and the output cavity mirror form a laser resonator; the input cavity mirror is the incident end face of the laser gain medium crystal with a dielectric film that has high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band; the output cavity mirror is the exit end face of the laser gain medium crystal with a dielectric film that has high transmittance for the 510 - 750 nm band and partial transmittance for the 475 - 495 nm band. This laser is also called a microchip laser.

[0020] Technical features and beneficial effects of the present invention:

[0021] (1) The present invention proposes to directly output high-efficiency 486.1 nm blue laser by using the Pr 3+ ion 3 P0→ 3 H4 energy level transition and the narrow-band resonator coating method. The fabricated blue laser has the characteristics of simple and compact structure, high stability, good monochromaticity, small volume, low power consumption, etc., and high-peak-power blue laser output can be obtained by the Q-switching method, meeting the requirements of high-power and high-integration miniaturized blue lasers for ocean exploration.

[0022] (2) By adjusting the parameters of the laser resonator, the present invention can achieve the output of blue-green dual-wavelength lasers at 486.1 nm and 520 nm to meet the requirements of duplex laser communication, multi-user communication, etc.

[0023] (3) The praseodymium ion-doped fluoride crystal involved in the present invention can be prepared by existing methods, and it is easy to obtain large-size high-quality single crystals with low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is a schematic structural diagram of Embodiment 1 of a all-solid-state laser directly emitting 486.1 nm blue laser based on a praseodymium-doped fluoride crystal according to the present invention.

[0025] Figure 2 FIG. is a schematic structural diagram of Embodiment 8 of a all-solid-state laser directly emitting 486.1 nm blue laser based on a praseodymium-doped fluoride crystal according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with the drawings and embodiments. The embodiments herein are only used to explain the present invention and are not used to limit the present invention.

[0027] The components used in the embodiments are all prior art unless otherwise specified.

[0028] Embodiment 1

[0029] An all-solid-state laser directly emitting 486.1 nm blue laser based on a praseodymium-doped fluoride crystal, the structure is as Figure 1 shown, which is sequentially arranged along the optical path by an excitation source 1, a focusing system 2, an input cavity mirror 3, a laser gain medium crystal 4, and an output cavity mirror 5. The excitation source 1 is a laser diode laser emitting a laser with a central wavelength of 442 nm, and the output mode is single-tube output; since the output spot quality of the excitation source is poor, the focusing system 2 includes a beam shaping system (consisting of 1 aspherical mirror and a pair of cylindrical lenses) and a focusing system (consisting of 1 convex lens); the input cavity mirror 3 is a plane mirror and is coated with a dielectric film with high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band; the laser gain medium crystal 4 is a Pr:LaF3 crystal with a doping concentration of 0.25 at.%, the tangential direction is the crystallographic axis a direction, and the size is 3×3×4 mm 3 , 3×3 mm 2 The two end faces are polished and coated with an antireflection film for the 440 - 750 nm band, and are located at the focal point of the focusing system; the output cavity mirror 5 is a plano-concave mirror with a curvature of 50 mm and is coated with a dielectric film with high transmittance for the 510 - 750 nm band and partial transmittance (transmittance is 0.5%) for the 475 - 495 nm band.

[0030] The pump light emitted by the excitation source is shaped, collimated and focused and then incident on the laser gain medium crystal. Through the oscillation of the laser resonator (composed of an input mirror and an output mirror), a 486.1 nm blue laser is generated and output from one end of the output mirror.

[0031] Examples 2 and 3

[0032] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, as described in Example 1, except that the doping concentrations of the laser gain medium crystal 4 (Pr:LaF3) are 0.1 at.% and 0.5 at.% respectively, and other conditions and components are the same as those described in Example 1.

[0033] Example 4

[0034] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, as described in Example 1, except that the sizes of the laser gain medium crystal 4 (Pr:LaF3) are 3×3×3 mm 3 and 3×3×6 mm 3 , and other conditions and components are the same as those described in Example 1.

[0035] Examples 5, 6 and 7

[0036] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, as described in Example 1, except that the laser gain medium crystal 4 is Pr:KY3F 10 crystal, and the doping concentrations of Pr 3+ ions are 0.3 at.%, 0.5 at.%, 0.9 at.% respectively, and other conditions and components are the same as those described in Example 1.

[0037] Example 8

[0038] A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, the structure is as Figure 2 shown, and it is composed of an excitation source 1, a focusing system 2, and a laser gain medium crystal 4 arranged in sequence along the optical path. The excitation source 1 is a laser diode laser emitting a laser with a central wavelength of 442 nm, and the output mode is single-tube output; since the output spot quality of the excitation source is poor, the focusing system 2 includes a beam shaping system (composed of 1 aspherical mirror and a pair of cylindrical lenses) and a focusing system (composed of 1 convex lens); the laser gain medium crystal 4 is a Pr:LaF3 crystal with a doping concentration of 0.25 at.%, the tangential direction is the crystallographic axis a direction, and the size is 3×3×4 mm 3 , 3×3 mm 2Both end faces are polished and coated with an antireflection film for the 440 - 750 nm band, and are located at the focal point of the focusing system; on the incident end face of the laser gain medium crystal 4, a dielectric film with high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band is coated, as represented by Figure 2 In Figure 2 , 6 represents that on the output end face, a dielectric film with high transmittance for the 510 - 750 nm band and partial transmittance (transmittance of 0.5%) for the 475 - 495 nm band is coated, as represented by Figure 2 In Figure 2 , 7 represents that the dielectric film 6 and the dielectric film 7 form a laser resonator.

[0039] The pump light emitted by the excitation source is incident on the laser gain medium crystal after shaping, collimation and focusing, and 486.1 nm blue laser light is generated through the oscillation of the laser resonator and output from the crystal output end.

[0040] Example 9

[0041] A all - solid - state laser directly emitting 486.1 nm blue laser light based on a praseodymium - doped fluoride crystal, as described in Example 1, the difference is that the input mirror 3 is coated with a dielectric film with high transmittance for the 440 - 445 nm and 540 - 750 nm bands and high reflectance for the 475 - 525 nm band, and the output mirror 5 is coated with a dielectric film with high transmittance for the 540 - 750 nm band and partial transmittance (transmittance of 1%) for 486.1 nm and partial transmittance (transmittance of 0.5%) for 520 nm. Other conditions and components are the same as those described in Example 1.

[0042] The pump light emitted by the excitation source is incident on the laser gain medium crystal after shaping, collimation and focusing, and 486.1 nm and 520 nm blue - green dual - wavelength laser lights are generated simultaneously through the oscillation of the laser resonator and output from one end of the output mirror.

Claims

1. A all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal, comprising an excitation source, a focusing system, a laser gain medium crystal and a laser resonator; characterized in that: The excitation source is a laser diode laser with a central emission wavelength of 440 - 445 nm; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions; the laser resonator is composed of an input mirror and an output mirror; the laser gain medium crystal is located between the input mirror and the output mirror, near the focus of the focusing system.

2. The all-solid-state laser based on directly emitting 486.1 nm blue laser with praseodymium-doped fluoride crystal as claimed in claim 1, characterized in that: The laser resonator is composed of an input mirror and an output mirror. The input mirror is coated with a dielectric film that has high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band. The output mirror is coated with a dielectric film that has high transmittance for the 510 - 750 nm band and partial transmittance for the 475 - 495 nm band.

3. The all-solid-state laser directly emitting 486.1 nm blue laser based on praseodymium-doped fluoride crystal as claimed in claim 1, wherein: The laser resonator is composed of the incident end face and the exit end face of the crystal coated with dielectric films. The incident end face is coated with a dielectric film that has high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band. The exit end face is coated with a dielectric film that has high transmittance for the 510 - 750 nm band and partial transmittance for the 475 - 495 nm band.

4. A all-solid-state laser based on a praseodymium-doped fluoride crystal directly emitting 486.1 nm blue laser light as claimed in any one of claims 1 - 3, characterized in that: The laser gain medium crystal is lanthanum fluoride (LaF3) or potassium yttrium fluoride (KY3F 10 ) crystal doped with praseodymium ions, the doping concentration of praseodymium ions is 0.05 at.% - 2 at.%, the light-transmitting surface is circular, square or rectangular, and after the light-transmitting surface is polished, an antireflection dielectric film is coated or no dielectric film is coated, and the length of the light-transmitting direction is 2 mm - 20 mm.

5. The all-solid-state laser based on a praseodymium-doped fluoride crystal directly emitting 486.1 nm blue laser light as claimed in claim 1, wherein: It includes an excitation source, a focusing system, an input mirror, a laser medium crystal, and an output mirror arranged in sequence along the optical path direction; the excitation source is a laser diode laser with a central emission wavelength of 440 - 445 nm, and the output mode is single-tube output; the focusing system consists of one aspherical mirror, a pair of cylindrical lenses, and one convex lens; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions; the input mirror is a plane mirror coated with a dielectric film that has high transmittance for the 440 - 445 nm and 510 - 750 nm bands and high reflectance for the 475 - 495 nm band; the output mirror is a plano-concave mirror with a curvature of 50 - 200 nm, coated with a dielectric film that has high transmittance for the 510 - 750 nm band and partial transmittance for the 475 - 495 nm band; this resonator outputs 486.1 nm blue laser light.

6. The all-solid-state laser based on a praseodymium-doped fluoride crystal directly emitting 486.1 nm blue laser light as claimed in claim 1, wherein: It includes an excitation source, a focusing system, an input mirror, a laser medium crystal, and an output mirror arranged in sequence along the optical path direction; the excitation source is a laser diode laser with a central emission wavelength of 440 - 445 nm, and the output mode is single-tube output; the focusing system consists of one aspherical mirror, a pair of cylindrical lenses, and one convex lens; the laser gain medium crystal is a fluoride crystal doped with praseodymium ions; the input mirror is a plane mirror coated with a dielectric film that has high transmittance for the 440 - 445 nm and 540 - 750 nm bands and high reflectance for the 475 - 525 nm band; the output mirror is a plano-concave mirror with a curvature of 50 - 200 nm, coated with a dielectric film that has high transmittance for the 540 - 750 nm band and partial transmittance for the 475 - 525 nm band; this resonator outputs both 486.1 nm and 520 nm blue-green dual-wavelength laser light.

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