Continuous wave yellow laser of neodymium-doped garnet activated medium

Abstract

The invention relates to the technical field of laser, in particular to a neodymium-doped garnet activated medium continuous wave yellow laser which comprises an excitation source, a focusing system, a laser medium crystal, a nonlinear optical crystal and a laser resonant cavity. The laser medium crystal and the nonlinear optical crystal are positioned in the laser resonant cavity; the laser resonant cavity is composed of an input mirror and an output mirror, and one side of a mirror cavity is plated with a dielectric film of a corresponding wave band. Pump light emitted by an excitation source is collimated by a focusing system, then enters a laser resonant cavity through an input mirror and is incident on a laser medium crystal, the laser medium crystal absorbs pump energy to generate energy level transition, and electron-phonon coupling laser is generated; and after the electron-phonon coupled laser is subjected to frequency conversion through the nonlinear optical crystal, continuous wave yellow laser is output from one end of the output mirror. The device has the characteristics of simple structure, high working stability and high temperature adaptability.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and more particularly to a continuous wave yellow laser of a neodymium-doped garnet active medium. Background Art

[0002] Yellow lasers (565-590nm) with wavelengths in the visually sensitive area are widely used in laser display, medical treatment, astronomy, etc. For example, in fluorescence microscopy, some fluorescent cells have absorption peaks in the yellow light band; in flow cytometry, yellow lasers with a wavelength of 565nm-590nm with stable power, low noise and good beam quality are required; when treating diabetic retinopathy, using 577nm yellow lasers can avoid unnecessary pain and possible damage to vision; yellow lasers with a wavelength of 589.3nm are also used to excite sodium atoms in the sky to form "artificial guide stars" to help correct image distortion. Therefore, yellow lasers are currently urgently needed key light sources.

[0003] At present, there are several technical means to achieve yellow light through all-solid-state laser technology: (1) Dy 3+ or Tb 3+ (1) Yellow lasers doped with gain media; (2) Yellow lasers that combine stimulated Raman scattering effect with frequency doubling effect, which can be used to obtain yellow laser emission in diamond, Ba(NO3)2, KGW and YVO4 crystals; (3) 1064nm and 1319nm lasers from Nd:YAG crystals generate yellow lasers through nonlinear sum-frequency technology. However, these methods are limited by low output power, complex equipment and high cost.

[0004] Neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal is one of the most commonly used solid laser gain media. Nd:YAG crystal has a complex energy level structure and rich electronic transition processes. Currently, laser operation with up to 28 different spectral lines has been achieved. Among them, 1064nm is its strongest luminescence line. Through the frequency doubling process, green light with a wavelength of 532nm can be obtained. 4 F 3 / 2 to 4 I 11 / 2The longest spectrum of the energy level transition line and the electronic transition can only reach 1122nm. Combined with the frequency doubling process, a 561nm yellow-green laser can be obtained [Optics Communications 281, 4088-4091 (2008)]. However, in the 1130-1180nm spectral range, Nd:YAG laser crystals do not have suitable electronic transition spectrum lines, so it is impossible to obtain 565-590nm yellow lasers by combining conventional lasers with nonlinear frequency doubling technology. In addition, the stimulated Raman gain coefficient of Nd:YAG is extremely low, and it is also impossible to obtain yellow lasers by combining self-Raman lasers with frequency doubling technology. At present, yellow lasers can only be generated by combining three crystals: laser crystal + Raman crystal + frequency doubling crystal. The device is complex and the cost is high.

[0005] In the process of luminescence of crystal materials, electron transitions are inevitably affected by the vibration of the surrounding lattice, thereby changing the energy transfer, resulting in the generation of new "virtual" energy levels, and transitions from high energy levels to new "virtual" energy levels, achieving the broadening of the emission spectrum, that is, using the electron-phonon coupling effect to expand the laser wavelength. By combining electron-phonon coupling with the frequency doubling effect, the laser wavelength in the visible light region can be further expanded. Neodymium-doped garnet crystals are one of the most widely used crystals. There are currently no reports on the direct generation of continuous wave yellow lasers by frequency doubling in Nd:YAG crystals. Summary of the invention

[0006] In view of this, the present invention provides a continuous wave yellow laser with neodymium-doped garnet activated medium, which only involves the combination of two crystals. It is simpler and has better stability than the previous device for generating yellow laser by combining three crystals with stimulated Raman combined with frequency doubling.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A neodymium-doped garnet activated medium continuous wave yellow laser, comprising: an excitation source, a focusing system, a laser medium crystal, a nonlinear optical crystal and a laser resonant cavity; the laser medium crystal and the nonlinear optical crystal are located in the laser resonant cavity; the laser resonant cavity is composed of an input mirror and an output mirror, and a dielectric film of a corresponding wavelength band is plated on one side of the mirror cavity;

[0009] The pump light emitted by the excitation source is collimated by the focusing system, enters the laser resonant cavity through the input mirror, and is incident on the laser medium crystal. The laser medium crystal absorbs the pump energy to undergo energy level transition, generating electron-phonon coupled laser. The electron-phonon coupled laser is frequency-converted by the nonlinear optical crystal, and outputs continuous wave yellow laser at one end of the output mirror.

[0010] Furthermore, the excitation source is a titanium sapphire laser or a laser diode laser, which emits a laser with a wavelength of 780nm-880nm; preferably, it is a laser diode laser with an emission wavelength of 780nm-880nm, which has a stable output wavelength and a high output power.

[0011] Furthermore, one side of the mirror cavity of the input mirror is coated with a dielectric film A, or the incident end face of the laser dielectric crystal is coated with a dielectric film A, and the dielectric film A has high transmittance at 780nm-880nm, 930nm-960nm, 1000nm-1130nm, 1320nm-1460nm and high reflectivity at 570-590nm, 1150nm-1300nm.

[0012] Furthermore, a dielectric film B is coated on one side of the cavity mirror of the output mirror, or a dielectric film B is coated on the output end face of the laser dielectric crystal, and the dielectric film B has high reflectivity in the 780nm-880nm band, high transmittance in the 570-590nm, 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm bands, and partially transmittance in the 1150nm-1300nm band.

[0013] By coating the input mirror with a dielectric film with high transmittance in the bands of 780nm-880nm, 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm, and coating the output mirror with a dielectric film with high transmittance in the bands of 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm, the absorption rate of the Nd:YAG crystal to the pump light can be improved, and the loss of the pump excitation light can be reduced; at the same time, the resonant cavity design of the present invention improves the loss of intrinsic electron transitions at 946nm, 1064nm, 1122nm, 1319nm, etc., so that the oscillation of the intrinsic electron transition in the laser cavity can be suppressed. By coating the input mirror with a dielectric film with high reflection in the 1150nm-1300nm band and the output mirror with a dielectric film with different transmittance in the 1150nm-1300nm band, the quality factor at 1150-1300nm is improved, which is conducive to the selective amplification of the transition of phonon-assisted activation and the realization of phonon-assisted laser oscillation. By coating the input mirror with a dielectric film with high reflection in the 570-590nm band and the output mirror with a dielectric film with high transmittance in the 570-590nm band, a high-power continuous wave yellow laser can be obtained. By coating the output mirror with a dielectric film with high reflection in the 780nm-880nm band, the effective absorption of the crystal for the excitation light can be increased.

[0014] Furthermore, the output mirror includes a first output mirror and a second output mirror; the input mirror, the first output mirror and the second output mirror form a three-mirror resonant cavity; the laser medium crystal is located at the beam waist position between the input mirror and the first output mirror, and is located at the focal position of the focusing system; the nonlinear optical crystal is located at the beam waist position between the first output mirror and the second output mirror; the laser medium crystal and the nonlinear optical crystal are both long crystals.

[0015] Furthermore, the laser medium crystal is a neodymium ion-doped yttrium aluminum garnet crystal, and the crystal tangent is <111> The doping concentration is 0.1%-2% in crystal direction, and the preferred doping concentration is 0.5%-1%.

[0016] Furthermore, the nonlinear optical crystal is an LBO crystal, which has high thermal stability, high damage threshold and wide transparency range.

[0017] Furthermore, the light-transmitting surfaces of the laser dielectric crystal and the nonlinear optical crystal are circular, square or rectangular, polished and coated with a dielectric film under certain conditions or uncoated, and the length in the light-transmitting direction is 0.5mm-50mm. Among them, the light-transmitting length of the laser dielectric crystal is preferably 4mm-15mm, and the light-transmitting length of the nonlinear optical crystal is preferably 10mm-15mm.

[0018] Furthermore, the nonlinear optical crystal is cut along a non-critical phase matching direction (θ=90°, φ=0°).

[0019] Furthermore, the focusing system is composed of a single or multiple convex lenses, which collimate and focus the pump light emitted by the excitation source into the laser medium crystal. The focal length of the focusing system is determined according to the usage, preferably 1-10 cm.

[0020] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention first broadens the emission spectrum of the laser medium crystal (neodymium-doped garnet laser crystal) through the electron-phonon coupling effect, and then performs frequency doubling conversion through the nonlinear optical LBO crystal to realize continuous wave yellow laser operation in the neodymium ion-doped garnet crystal, and obtains a continuous yellow laser with a wavelength range of 565-590nm. Compared with the traditional neodymium-doped garnet laser crystal combined with frequency doubling to obtain green laser, the electron-phonon coupling laser crystal achieves wavelength expansion and precise control, the device design is relatively simple, and the wavelength tuning range is wide.

[0022] Compared with the traditional neodymium-doped garnet laser crystal combined with Raman frequency shift and then frequency doubling to obtain yellow light laser, which requires the use of three crystals, the electron-phonon coupled laser crystal only involves one nonlinear optical conversion effect, which reduces the number of components and has the advantages of simple and compact structure, good laser performance stability, and strong temperature adaptability.

[0023] The present invention is the first to combine frequency doubling with neodymium ion-doped yttrium aluminum garnet crystal to obtain continuous wave yellow laser, which can meet the application needs of specific scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 A schematic diagram of the structure of a continuous wave yellow laser with a neodymium-doped garnet active medium provided by the present invention;

[0026] Figure 2 The neodymium ion-doped yttrium aluminum garnet crystal provided by the present invention realizes a yellow light laser wavelength output spectrum through frequency doubling. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, the embodiment of the present invention discloses a continuous wave yellow laser of neodymium-doped garnet activated medium, comprising: an excitation source 1, a focusing system 2, a laser medium crystal 4, a nonlinear optical crystal 5 and a laser resonant cavity; the laser medium crystal 4 and the nonlinear optical crystal 5 are located in the laser resonant cavity; the laser resonant cavity is composed of an input mirror 3 and an output mirror 6, and a dielectric film of a corresponding wavelength band is plated on one side of the mirror cavity;

[0029] The pump light emitted by the excitation source 1 is collimated by the focusing system 2, enters the laser resonant cavity through the input mirror 3, and is incident on the laser medium crystal 4. The laser medium crystal 4 absorbs the pump energy and undergoes energy level transition to generate electron-phonon coupled laser; the electron-phonon coupled laser is then frequency converted by the nonlinear optical crystal 5, and outputs continuous wave yellow light laser 7 at one end of the output mirror 6.

[0030] Among them, one side of the mirror cavity of the input mirror 3 is coated with a dielectric film A, or the incident end face of the laser dielectric crystal 4 is coated with a dielectric film A, and the dielectric film A has high transmittance at 780nm-880nm, 930nm-960nm, 1000nm-1130nm, 1320nm-1460nm and high reflectivity at 570-590nm, 1150nm-1300nm.

[0031] One side of the cavity mirror of the output mirror 6 is coated with a dielectric film B, or the output end face of the laser dielectric crystal 4 is coated with a dielectric film B. The dielectric film B has high reflectivity in the 780nm-880nm band, high transmittance in the 570-590nm, 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm bands, and partially transmits the 1150nm-1300nm band.

[0032] The output mirror 6 includes a first output mirror 61 and a second output mirror 62; the input mirror 3, the first output mirror 61 and the second output mirror 62 form a three-mirror resonant cavity; the laser medium crystal 4 is located at the beam waist position between the input mirror 3 and the first output mirror 61; the nonlinear optical crystal 5 is located at the beam waist position between the first output mirror 61 and the second output mirror 62; the laser medium crystal 4 and the nonlinear optical crystal 5 are both long crystals.

[0033] Laser medium crystal 4 is a neodymium ion-doped yttrium aluminum garnet crystal, and the crystal tangent direction is <111> The laser medium crystal 4 has a circular, square or rectangular light-transmitting surface, which is polished and coated with a dielectric film of certain conditions or not coated, and a light-transmitting direction length of 0.5mm-50mm, preferably 4mm-15mm.

[0034] The nonlinear optical crystal is an LBO crystal, the light-transmitting surface is round, square or rectangular, the light-transmitting surface is polished and coated with a dielectric film under certain conditions or is not coated, and the length in the light-transmitting direction is 0.5mm-50mm, preferably 10mm-15mm. The nonlinear optical crystal is cut along the noncritical phase matching direction (θ=90°, φ=0°).

[0035] The present invention is further described below with reference to different embodiments.

[0036] Example 1

[0037] The continuous wave yellow light laser doped with garnet activated medium combined with frequency doubling is composed of an excitation source 1, a laser focusing system 2, an input mirror 3, a laser crystal 4, a first output mirror 61, a nonlinear optical crystal 5 and a second output mirror 62 arranged in sequence, wherein the excitation source 1 is a laser diode laser with an emission wavelength of 808nm; the laser focusing system 2 is a focusing mirror with a focal length of 5cm; the input mirror 3 is a flat mirror, which is plated with a dielectric film with high transmittance to 780nm-880nm, 930nm-960nm, 1000nm-1130nm, 1320nm-1460nm and high reflectance to 570-590nm, 1150nm-1300nm; the laser gain medium 4 is a yttrium aluminum garnet crystal doped with neodymium ions, the neodymium ion doping concentration is 0.6%, and the light transmission direction is <111> Crystal orientation, crystal length is 4mm, light-transmitting surface is 3*3mm 2 , double-sided polished and plated with a dielectric film with high transmittance of 780nm-880nm, 1000nm-1460nm; nonlinear optical crystal 5 is LBO crystal, with a crystal length of 15mm and a light-transmitting surface of 3*3mm 2 , cut along the non-critical phase matching direction (θ=90°, φ=0°), double-sided polished and coated with a dielectric film for anti-reflection of 570-590nm and 1150nm-1300nm; the first output mirror 61 and the second output mirror 62 are concave mirrors with a focal length of 100mm, coated with a dielectric film with high reflection of 780nm-880nm, high transmission of 570-590nm, 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm and partial transmission of 1150nm-1300nm (transmittance T oc =0.1%) dielectric film. The resonant cavity is composed of a three-mirror resonant cavity consisting of an input mirror 3, a first output mirror 61 and a second output mirror 62; the laser crystal 4 and the frequency doubling crystal 5 are both long crystals and are placed at the two arm waists of the three-mirror resonant cavity. By increasing the excitation source power, yellow laser outputs of 575.5nm and 583nm can be achieved respectively. The wavelengths are as follows Figure 2 As shown, Figure 2 (a) in FIG. 1 is a 575.5 nm yellow laser output spectrum, where the horizontal axis is wavelength (nm) and the vertical axis is intensity (arbitrary unit). Figure 2 (b) in the figure is the output spectrum of 583nm yellow laser, where the horizontal axis is wavelength (nm) and the vertical axis is intensity (arbitrary unit).

[0038] Example 2

[0039] As described in Example 1, the difference is that the excitation source is a laser diode laser with an emission wavelength of 880nm, and other conditions are consistent with those described in Example 1.

[0040] Example 3

[0041] As described in Example 1, the difference is that the focusing system is composed of a combined convex lens pair with focal lengths of 10 cm and 5 cm or focal lengths of 5 cm and 2.5 cm, and other conditions are consistent with those described in Example 1.

[0042] Example 4

[0043] As described in Example 1, the difference is that the laser medium crystal 4 is a garnet laser crystal such as Nd:YGG, Nd:GGG, Nd:LuAG, Nd:LuGG, Nd:GSAG, Nd:CNGG, etc., and the other conditions are the same as those described in Example 1.

[0044] Example 5

[0045] As described in Example 1, the difference is that the length of the laser medium crystal 4, a neodymium ion-doped yttrium aluminum garnet crystal, is 6 mm, 8 mm or 10 mm, and the other conditions are consistent with those described in Example 1.

[0046] Example 6

[0047] As described in Example 1, the difference is that the direction of the laser medium crystal 4 neodymium ion doped yttrium aluminum garnet crystal is <100> , <110> or <101> , other conditions are consistent with those described in Example 1.

[0048] Example 7

[0049] Similar to Example 1, the difference is that the laser medium crystal 4 is a yttrium aluminum garnet crystal doped with neodymium ions, and the doping concentration is 0.5%, 0.8% or 1%. Other conditions are consistent with those described in Example 1.

[0050] Example 8

[0051] Similar to Example 1, the difference is that the length of the nonlinear optical crystal 5, the LBO crystal, is 10 mm, 12 mm or 16 mm, and the other conditions are consistent with those described in Example 1.

[0052] Example 9

[0053] Similar to Example 1, the difference is that the nonlinear optical crystal 5 selects BBO crystal, KTP crystal, or PPLN crystal for nonlinear frequency conversion, and other conditions are consistent with those described in Example 1.

[0054] Example 10

[0055] Similar to Example 1, the difference is that the curvature of the output mirror 6 is 50 mm, 100 mm, 150 mm or 200 mm, and other conditions are consistent with those described in Example 1.

[0056] The embodiments of the present invention are not limited to the above embodiments. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. The relevant parts can be referred to the method part.

[0057] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A neodymium-doped garnet active medium continuous wave yellow laser, characterized in that: include: An excitation source, a focusing system, a laser medium crystal, a nonlinear optical crystal and a laser resonant cavity; the laser medium crystal and the nonlinear optical crystal are located in the laser resonant cavity; the laser resonant cavity is composed of an input mirror and an output mirror, and a dielectric film of a corresponding wavelength band is plated on one side of the mirror cavity; The pump light emitted by the excitation source is collimated by the focusing system, enters the laser resonant cavity through the input mirror, and is incident on the laser medium crystal. The laser medium crystal absorbs the pump energy to undergo energy level transition, generating electron-phonon coupled laser. The electron-phonon coupled laser is frequency-converted by the nonlinear optical crystal, and outputs continuous wave yellow laser at one end of the output mirror.

2. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The excitation source is a titanium sapphire laser or a laser diode laser, and the wavelength of the laser emitted by the laser is 780nm-880nm.

3. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: One side of the input mirror cavity is coated with a dielectric film A, or the incident end face of the laser dielectric crystal is coated with a dielectric film A, and the dielectric film A has high transmittance at 780nm-880nm, 930nm-960nm, 1000nm-1130nm, 1320nm-1460nm and high reflectivity at 570-590nm, 1150nm-1300nm.

4. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: One side of the cavity mirror of the output mirror is coated with a dielectric film B, or the output end face of the laser dielectric crystal is coated with a dielectric film B, the dielectric film B has high reflectivity in the 780nm-880nm band, high transmittance in the 570-590nm, 930nm-960nm, 1000nm-1130nm and 1320nm-1460nm bands and partially transmits the 1150nm-1300nm band.

5. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The output mirror comprises a first output mirror and a second output mirror; the input mirror, the first output mirror and the second output mirror form a three-mirror resonant cavity; the laser medium crystal is located at the beam waist position between the input mirror and the first output mirror; the nonlinear optical crystal is located at the beam waist position between the first output mirror and the second output mirror; the laser medium crystal and the nonlinear optical crystal are both long crystals.

6. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The laser medium crystal is a neodymium ion-doped yttrium aluminum garnet crystal, and the crystal tangent direction is <111> Crystal direction, doping concentration is 0.1%-2%.

7. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The nonlinear optical crystal is an LBO crystal.

8. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The light-transmitting surfaces of the laser medium crystal and the nonlinear optical crystal are circular, square or rectangular, are polished and coated with a medium film under certain conditions or are not coated, and have a light-transmitting direction length of 0.5 mm-50 mm.

9. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The nonlinear optical crystal is cut along a noncritical phase matching direction (θ=90°, φ=0°).

10. The Nd-doped garnet active medium continuous wave yellow laser according to claim 1, characterized in that: The focusing system is composed of a single or multiple convex lenses, which collimate and focus the pump light emitted by the excitation source into the laser medium crystal.

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