Femtosecond disc laser capable of generating human eye safe wave band

Abstract

The invention discloses a femtosecond disc laser capable of generating human eye safe wave bands, and belongs to the technical field of femtosecond lasers. The femtosecond disc laser capable of generating the human eye safe wave band comprises a pumping source, a disc crystal, a pumping cavity and a resonant cavity, the pumping cavity enables pumping light emitted by the pumping source to penetrate through the disc laser crystal for multiple times and then excites and generates oscillation laser; in the resonant cavity, a first branch comprises a high-dispersion mirror and an output mirror which are sequentially arranged along a light path; the oscillation laser is transmitted to the output mirror along the first branch, then returns to the disc laser crystal along the original path, and is reflected to the second branch; the second branch comprises a first concave mirror, a second concave mirror, a Cr < 4 + >: YAG crystal and a high-reflection mirror which are sequentially arranged along the light path; the Cr < 4 + >: YAG crystal is used as a passive mode-locking device and is also used as a gain medium to generate a femtosecond laser pulse sequence of a human eye safe wave band. The femtosecond disc laser is simple in structure, and can generate stable femtosecond laser output with a specific wave band.

Description

Technical Field

[0001] The present invention belongs to the field of disk lasers, and more specifically, relates to a femtosecond disk laser that generates a human eye-safe wavelength band. Background Art

[0002] The disk technology is to make the gain medium into a thin sheet structure with a diameter of more than 10mm and a thickness of 100-300μm. At the same time, the disk is welded to a tungsten copper heat sink or glued to a diamond heat sink with better thermal conductivity, and the heat on the disk is efficiently taken away by impact water cooling, so that the crystal has only one-dimensional thermal gradient distribution, effectively avoiding problems such as thermal lensing, thermal distortion and nonlinear excitation of the gain medium, and providing a guarantee for the generation of femtosecond lasers with high peak power, high average power and high beam quality.

[0003] At present, high-power eye-safe femtosecond lasers are mainly produced based on bulk crystals and nonlinear frequency conversion. The main methods used include using Cr 4+ :YAG crystal combined with passive mode-locking mechanism, femtosecond Raman frequency shift and optical parametric oscillator, etc., femtosecond Raman frequency shift and optical parametric oscillator, etc., can achieve femtosecond laser output in a specific band through these methods. However, there are some problems with existing lasers. For example, the use of bulk crystals is limited by the thermal effect and thermal distortion of the crystal under high-power pumping conditions. The average power of the femtosecond pulse of the constructed all-solid-state femtosecond laser is only in the milliwatt range without subsequent amplification. The low average power will greatly reduce the signal-to-noise ratio of the femtosecond pulse laser. The use of femtosecond Raman frequency shift and optical parametric oscillation technology is limited by self-steepening, stimulated Raman scattering, and nonlinear walk-off, and the femtosecond laser conversion efficiency is low. Therefore, how to find a method that can directly output high-power femtosecond pulses in the human eye-safe band has become an important problem that needs to be solved at present. Summary of the invention

[0004] In view of the defects of the prior art and the need for improvement, the present invention provides a femtosecond laser that generates a waveband safe for human eyes, aiming to solve the problem that the existing lasers cannot directly generate high-power femtosecond laser pulse sequences in the waveband safe for human eyes.

[0005] To achieve the above-mentioned object, the present invention provides a femtosecond disk laser that generates an eye-safe band, characterized in that it comprises: a pump source, a disk laser crystal, a pump cavity and a resonant cavity;

[0006] The pump cavity is arranged on the output light path of the pump source; the disk laser crystal is arranged in the pump cavity; the pump cavity makes the pump laser emitted by the pump source pass through the disk laser crystal for multiple times and then excites the disk laser crystal to generate oscillating laser;

[0007] The resonant cavity is arranged on one side of the output of the oscillating laser describing the disk laser crystal, and the resonant cavity comprises a first branch and a second branch;

[0008] The first branch includes a dispersion mirror group, a hard aperture and an output mirror arranged in sequence along the optical path; the hard aperture is used to assist passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror, a part of the laser is output through the output mirror, and the remaining laser returns to the disk laser crystal along the original path and is reflected to the second branch;

[0009] The second branch includes a first concave mirror, a second concave mirror, a Cr 4+ : YAG crystal and high reflective mirror; the focus of the first concave mirror and the second concave mirror coincides, the Cr 4+ : The YAG crystal is located at the focus, and the distance between the first concave mirror and the second concave mirror is located at the center of the stable region of the resonant cavity;

[0010] The Cr 4+ :YAG crystal is used as a saturable absorber for passive mode locking. 4+ :YAG crystal is also used as a gain medium to generate a femtosecond laser pulse sequence in the human eye-safe band under the action of an oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror, returns to the disk laser crystal along the original path, enters the first branch again after being reflected by the disk laser crystal, and the output mirror outputs the femtosecond laser pulse sequence in the human eye-safe band.

[0011] Optionally, the disk laser crystal is a Yb:YAG crystal, wherein Yb 3+ The doping concentration is 7%;

[0012] The Cr 4+ Cr:YAG crystal 4+ The doping concentration ranges from 2% to 7%, and the Cr 4+ :The length of YAG crystal ranges from 10mm to 30mm;

[0013] The central wavelength of the femtosecond laser pulse sequence in the human eye-safe band is 1500 nm.

[0014] Optionally, the Cr 4+ : Both sides of the YAG crystal surface are coated with broadband anti-reflection films for the 1000nm-1070nm and 1300-1600nm bands, with a transmittance greater than 99.9%.

[0015] Optionally, the light-facing surfaces of the dispersion mirror group, the first concave mirror, the second concave mirror and the high-reflection mirror are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, and the reflectivity is greater than 99.9%.

[0016] Optionally, the dispersion mirror group includes a first high dispersion mirror and a second high dispersion mirror arranged in sequence along the optical path.

[0017] Optionally, the light-facing surface of the output mirror is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and a film layer that partially transmits the 1300-1600nm band, and the transmittance ranges from 1% to 20%;

[0018] The light-emitting surface of the output mirror is coated with an anti-reflection film for oscillating lasers in the 1300-1600nm band.

[0019] Optionally, the disk laser crystal is coated with an anti-reflection film for the pump laser and the oscillating laser on the side facing the resonant cavity, and is coated with a high-reflection film for the pump laser and the oscillating laser on the side facing away from the resonant cavity.

[0020] Optionally, the surface of the disk laser crystal coated with a high-reflection film is fixed on a water-cooled heat sink.

[0021] Optionally, the femtosecond disk laser further comprises a crystal fixture;

[0022] The crystal holder holds the Cr 4+ :YAG crystal, the crystal fixture is provided with external circulating cooling water for cooling the Cr 4+ :YAG crystal for heat dissipation.

[0023] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0024] 1. The present invention provides a femtosecond disk laser that generates a specific wavelength band. It uses a disk laser crystal that is similar to a one-dimensional thin sheet as a gain medium. It can effectively dissipate heat under high-power pumping and minimize the generation of thermal effects. The small amount of heat generated can be efficiently removed through a stroke-type water-cooling structure. Therefore, the disk crystal is more supportive of high-power pumping conditions, so that high-power femtosecond lasers can be output, and the resonant cavity also has a higher average power. A passive saturable absorber (Cr) whose absorption spectrum range includes the central wavelength of the oscillating laser generated by the disk laser crystal is used. 4+:YAG crystal), which is used for passive mode locking. At the same time, it is also used as a gain medium to generate a femtosecond laser pulse sequence in the target band (eye-safe band) under the action of the oscillating laser; thereby directly generating high-power, eye-safe femtosecond laser pulses, and broadening the application scenarios of femtosecond disk lasers.

[0025] 2. The present invention provides a femtosecond disk laser that generates a specific wavelength band, using a Yb:YAG disk as a gain medium, the disk is a thin disk with a thickness of 130 μm and a diameter of 10 mm; Cr 4+ :YAG crystal is used as a passive mode-locking device and as a gain medium for the generation of eye-safe band lasers, directly outputting high-power eye-safe band femtosecond laser output in the resonant cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention provides a schematic structural diagram of a femtosecond disk laser that generates a specific wavelength band;

[0027] The reference numerals in the accompanying drawings are as follows:

[0028] 1. Pump source, 2. Disk laser crystal, 3. Pump cavity, 4. Resonant cavity, 5. Cr 4+ :YAG crystal, 6. first high dispersion mirror, 7. second high dispersion mirror, 8. hard aperture, 9. output mirror, 10. first concave mirror, 11. second concave mirror, 12. high reflection mirror. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The contents involved in the above embodiment are described below in conjunction with a preferred embodiment.

[0031] like Figure 1 As shown, a femtosecond disk laser generating a human eye-safe wavelength band comprises: a pump source 1, a disk laser crystal 2, a pump cavity 3 and a resonant cavity 4;

[0032] The pump cavity 3 is arranged on the outgoing light path of the pump source 1; the disk laser crystal 2 is arranged in the pump cavity 3; the pump cavity 3 enables the pump laser emitted by the pump source 1 to pass through the disk laser crystal 2 multiple times and then excite the disk laser crystal 2 to generate oscillating laser;

[0033] The resonant cavity 4 is arranged on one side of the output of the oscillating laser describing the disk laser crystal, and the resonant cavity 4 includes a first branch and a second branch;

[0034] The first branch includes a dispersion mirror group, a hard aperture 8 and an output mirror 9 arranged in sequence along the optical path; the hard aperture 8 is used to assist passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror 9, a part of the laser is output through the output mirror 9, and the remaining laser returns to the disk laser crystal 2 along the original path and is reflected to the second branch;

[0035] The second branch includes a first concave mirror 10, a second concave mirror 11, a Cr 4+ : YAG crystal 5 and high reflector 12; the focus of the first concave mirror 11 and the second concave mirror 11 coincide with each other, the Cr 4+ : The YAG crystal 5 is located at the focus, and the distance between the first concave mirror 10 and the second concave mirror 11 is located at the center of the stable region of the resonant cavity;

[0036] The Cr 4+ :YAG crystal 5 is used as a saturable absorber for passive mode locking, and the Cr 4+ :YAG crystal is also used as a gain medium to generate a femtosecond laser pulse sequence in the human eye-safe band under the action of an oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror 12, returns along the original path to the disk laser crystal 2, and enters the first branch again after being reflected by the disk laser crystal 2, and the output mirror 9 outputs the femtosecond laser pulse sequence in the human eye-safe band.

[0037] The central wavelength of the oscillating laser generated by the disk laser crystal 2 is within the Cr 4+ :YAG crystal 5 absorption spectrum range, the oscillation laser as the Cr 4+ : The pump light source of YAG crystal 5 generates femtosecond laser pulse sequences in the human eye-safe band.

[0038] In order to make the disk laser produce stable and sustainable femtosecond pulse output without increasing the structural complexity and energy loss, the present invention provides a femtosecond disk laser that produces a human eye-safe band, using Cr 4+ :YAG crystal 5 is used as a saturable absorber for passive mode locking in the 1030nm band. At the same time, since the central wavelength of the oscillating laser generated by the disk laser crystal 2 is in the selected Cr 4+ :YAG crystal 5 fluorescence absorption spectrum range, therefore, Cr 4+The YAG crystal 5 is also used as a gain medium to generate a femtosecond laser pulse sequence in the human eye-safe band under the action of the oscillating laser generated by the disk laser crystal 2. The width of the femtosecond laser pulse sequence output by the femtosecond disk laser reaches the femtosecond level, and the femtosecond laser pulse has high power and high stability, which significantly simplifies the design and operation of the device.

[0039] The disk laser crystal 2 acts as a gain medium, absorbing the energy generated by the pump laser to generate an oscillating laser. At the same time, the disk laser crystal 2 acts as a return mirror of the resonant cavity to reflect the oscillating laser. Therefore, different dielectric films are plated on both sides of the disk laser crystal 2. The side facing the resonant cavity is plated with an anti-reflection film for the pump laser and the oscillating laser, and the side facing away from the resonant cavity is plated with a high-reflection film for the pump laser and the oscillating laser. The surface of the disk laser crystal 2 plated with the high-reflection film is fixed on a water-cooled heat sink with a stroke structure.

[0040] Optionally, according to the mode distribution in the cavity, hard apertures 8 of different sizes are set at different positions in the cavity to increase the diffraction loss in the cavity to assist in mode locking.

[0041] like Figure 1 As shown, the pump source 1 is used to generate pump laser, and semiconductor laser, fiber laser and solid laser etc. can be selected. In this embodiment, a semiconductor laser with fiber coupling output is specifically used as the pump source, and the pump laser wavelength is 940nm or 969nm. In this embodiment, the pump cavity 3 includes a parabolic mirror and a series of reentrant prisms, which are placed in the optical path between the pump source 1 and the disk laser crystal 2 according to a set rule. The disk laser crystal 2 is placed at the focus of the parabolic mirror, and the input pump light is focused on the disk crystal 2 after multiple reflections of the parabolic mirror and the reentrant prism. The disk laser crystal 2 adopts a disk-shaped Yb:YAG (doping concentration is 7%) laser crystal with a diameter of 10mm and a thickness of 130μm. Its material is a Yb:YAG material with mature technology, which is used to provide a gain medium for 1030nm laser generation, and is arranged in the pump cavity 3. The pump cavity 3 allows the pump laser emitted by the pump source 1 to pass through the disk laser crystal 2 multiple times and then excite the disk laser crystal 2 to generate oscillating laser.

[0042] Furthermore, in this embodiment, a 48-pass pump structure is used, that is, the pump laser passes through the disk laser crystal 2 48 times, which greatly improves the absorption efficiency of the disk crystal for the pump light. In other embodiments, a 24-pass pump structure, a 36-pass pump structure, or a higher 72-pass pump structure may also be used according to actual needs.

[0043] In this embodiment, the resonant cavity 4 is used to output femtosecond pulses in a wide band of 1300-1600 nm, which is arranged on one side where the oscillating laser is output from the disk laser crystal, and includes a first branch and a second branch;

[0044] In this embodiment, the dispersion mirror specifically includes a first high-dispersion mirror 6 and a second high-dispersion mirror 7 which are sequentially arranged along the optical path; after the oscillating laser is incident from the disk laser crystal 2 to the first branch, it is first incident on the first high-dispersion mirror 6, and then reflected on the second high-dispersion mirror 7, and then reflected on the output mirror 9, part of the laser light is output through the output mirror 9, and the remaining laser light is reflected by the output mirror 6, returns to the disk laser crystal 2 along the original path, and is reflected to the second branch.

[0045] In this femtosecond disk laser, Cr 4+ :YAG crystal 5 is used as a modulation device for passive mode locking in the 1030nm band. 4+ :YAG crystal 5 has a strong fluorescence absorption spectrum in the range of 970nm-1100nm; therefore, the 1030nm femtosecond laser in the resonant cavity can be used as Cr 4+ : The pump light source generated by YAG crystal femtosecond laser in the human eye-safe band.

[0046] The disk laser crystal 2 of the femtosecond disk laser is a Yb:YAG crystal, which produces an oscillating laser with a central wavelength of 1030nm. The oscillating laser oscillates back and forth between the first branch, the disk laser crystal and the second branch, and is continuously irradiated by Cr 4+ :YAG crystal is modulated to form a high-power stable femtosecond laser pulse sequence with a central wavelength of 1030nm.

[0047] Furthermore, Cr 4+ :YAG crystal 5 continuously absorbs the 1030nm band femtosecond laser in the resonant cavity. When the gain of the 1300-1600nm band laser is greater than the loss, a broadband human eye-safe band femtosecond laser will be generated in the resonant cavity, and it will be continuously amplified by the reflector in the resonant cavity to form a stable pulse sequence, and part of it will be output through the output mirror 6, and the remaining part will return to the disk laser crystal 2 along the original path and be reflected to the second branch, realizing the round-trip oscillation of the oscillating laser in the resonant cavity.

[0048] Furthermore, Cr 4+ : The length of YAG crystal 5 is selected in the range of 10mm-30mm, Cr 4+ The doping concentration of the ions can be selected within the range of 2%-7%, that is, different lengths of the crystals and doping concentrations are combined with each other and adjusted accordingly according to experimental phenomena.

[0049] In order to further reduce the energy loss in the resonant cavity, Cr 4+ : The light-transmitting surface of the YAG crystal 5 is optimized. Specifically, the Cr 4+: Both sides of the YAG crystal surface are coated with broadband anti-reflection films for the 1000nm-1070nm and 1300-1600nm bands, with a transmittance greater than 99.9%.

[0050] Optionally, the light-facing surfaces of the dispersion mirror group, the first concave mirror 10, the second concave mirror 11 and the high-reflection mirror 12 are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, and the reflectivity is greater than 99.9%.

[0051] Optionally, the light-facing surface of the output mirror 9 is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and a film layer that partially transmits the 1300-1600nm band, and the transmittance ranges from 1% to 20%;

[0052] The light-emitting surface of the output mirror 9 is coated with an anti-reflection film for oscillating lasers in the 1300-1600nm band.

[0053] The reflective surface of the output mirror 9 is also coated with a high-reflective film for 1000nm-1070nm and oscillating lasers, and the reflectivity is greater than 99.9%.

[0054] The front surfaces of the first concave mirror 10, the second concave mirror 11 and the high-reflection mirror 12 in the resonant cavity 4 are coated with a 1300-1600nm high-reflection film, and the front surface of the output mirror 9 is coated with a 1300-1600nm partial transmission film, thereby ensuring that the 1300-1600nm femtosecond laser reciprocates and oscillates between the first branch, the disk laser crystal and the second branch to enhance, and finally output high-power eye-safe band femtosecond laser pulses.

[0055] Optionally, the femtosecond disk laser further comprises a crystal fixture;

[0056] The crystal holder holds the Cr 4+ :YAG crystal 5, the crystal fixture is provided with external circulating cooling water for cooling the Cr 4+ :YAG crystal 5 for heat dissipation.

[0057] Furthermore, Cr 4+ :YAG crystal 5 is wrapped with silver foil and clamped by a crystal fixture. The crystal fixture is made of copper. The crystal fixture has external circulating cooling water and adjusts the temperature according to the average power in the resonant cavity. The wrapped silver foil is used for Cr 4+ :YAG crystal 5 and copper material fit more closely, improving the cooling effect.

[0058] Take the above-mentioned femtosecond disk laser and turn Cr 4+:YAG crystal can be used as a component for passive mode locking in the 1μm band and as a gain medium for eye-safe femtosecond laser generation, and can obtain stable high-power femtosecond laser pulses in the eye-safe band (target band), which significantly simplifies the design and operation of the device. The femtosecond disk laser that generates a specific band provided by the present invention has a simple and compact structure and can be widely used in the fields of laser radar, industrial ranging, and ophthalmic surgery, and has good development and application prospects.

[0059] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A femtosecond disk laser that generates an eye-safe wavelength, characterized in that: include: Pump source (1), disk laser crystal (2), pump cavity (3) and resonant cavity (4); The pump cavity (3) is arranged on the output light path of the pump source (1); the disk laser crystal (2) is arranged in the pump cavity (3); the pump cavity (3) enables the pump laser emitted by the pump source (1) to pass through the disk laser crystal (2) multiple times and then excite the disk laser crystal (2) to generate oscillating laser; The resonant cavity (4) is arranged on one side of the oscillating laser describing the output of the disk laser crystal, and the resonant cavity (4) comprises a first branch and a second branch; The first branch comprises a dispersion mirror group, a hard aperture (8) and an output mirror (9) arranged in sequence along the optical path; the hard aperture (8) is used to assist passive mode locking; after the oscillating laser is transmitted along the first branch to the output mirror (9), a portion of the laser is output through the output mirror (9), and the remaining laser returns to the disk laser crystal (2) along the original path and is reflected to the second branch; The second branch comprises a first concave mirror (10), a second concave mirror (11), a Cr 4+ :YAG crystal (5) and a high reflective mirror (12); the focal points of the first concave mirror (11) and the second concave mirror (11) coincide with each other, and the Cr 4+ : the YAG crystal (5) is located at the focus, and the distance between the first concave mirror (10) and the second concave mirror (11) is located at the center of the stable region of the resonant cavity; The Cr 4+ :YAG crystal (5) is used as a saturable absorber for passive mode locking. 4+ The YAG crystal is also used as a gain medium for generating a femtosecond laser pulse sequence in the human eye-safe band under the action of the oscillating laser; the femtosecond laser pulse sequence in the human eye-safe band is reflected by the high-reflection mirror (12), returns to the disk laser crystal (2) along the original path, and enters the first branch again after being reflected by the disk laser crystal (2), and the output mirror (9) outputs the femtosecond laser pulse sequence in the human eye-safe band.

2. The femtosecond disk laser according to claim 1, characterized in that: The disk laser crystal (2) is a Yb:YAG crystal, wherein Yb 3+ The doping concentration is 7%; The Cr 4+ :Cr of YAG crystal (5) 4+ The doping concentration ranges from 2% to 7%, and the Cr 4+ : The length of the YAG crystal (5) ranges from 10 mm to 30 mm; The central wavelength of the femtosecond laser pulse sequence in the human eye-safe band is 1500 nm.

3. The femtosecond disk laser according to claim 2, characterized in that: The Cr 4+ Broadband anti-reflection films for the wavelength bands of 1000nm-1070nm and 1300-1600nm are coated on both sides of the surface of the YAG crystal (5), and the transmittance is greater than 99.9%.

4. The femtosecond disk laser according to claim 2, characterized in that: The light-facing surfaces of the dispersion mirror group, the first concave mirror (10), the second concave mirror (11) and the high-reflection mirror (12) are coated with broadband high-reflection films for the 1000nm-1070nm band and the 1300-1600nm band, with a reflectivity greater than 99.9%.

5. The femtosecond disk laser according to claim 4, characterized in that: The dispersion mirror group comprises a first high dispersion mirror (6) and a second high dispersion mirror (7) which are arranged in sequence along the optical path.

6. The femtosecond disk laser according to claim 2, characterized in that: The light-facing surface of the output mirror (9) is coated with a film layer that fully reflects the oscillating laser in the 1000nm-1070nm band and a film layer that partially transmits the 1300-1600nm band, with a transmittance range of 1% to 20%; The light-emitting surface of the output mirror (9) is coated with an anti-reflection film for oscillating lasers in the 1300-1600nm band.

7. The femtosecond disk laser according to any one of claims 1 to 6, characterized in that: The disk laser crystal (2) is coated with an anti-reflection film for pump laser and oscillating laser on the side facing the resonant cavity (4), and is coated with a high-reflection film for pump laser and oscillating laser on the side facing away from the resonant cavity (4).

8. The femtosecond disk laser according to claim 7, characterized in that: The surface of the disk laser crystal (2) coated with a high-reflection film is fixed on a water-cooled heat sink.

9. The femtosecond disk laser according to claim 1, characterized in that: The femtosecond disk laser also includes a crystal fixture; The crystal holder holds the Cr 4+ :YAG crystal, the crystal fixture is provided with external circulating cooling water for cooling the Cr 4+ :YAG crystal for heat dissipation.

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