Regenerative amplifier and method for improving output power by intracavity excitation of high-order modes

Abstract

The present invention relates to the field of solid ultrafast lasers, and particularly to a regenerative amplifier and method for increasing the output power by intracavity excitation of high-order modes, including a ytterbium-doped fiber oscillator, a pulse stretcher, a crystal regenerative amplifier module, and a pulse compressor arranged in the optical path sequence; the ytterbium-doped fiber oscillator is used to generate initial laser pulses; the pulse stretcher is used to broaden the initial laser pulses; the crystal regenerative amplifier is used to amplify the laser pulses; the pulse compressor is used to compress the amplified laser pulses; by rotating the pump-end mirror, the pump light is obliquely incident into the crystal, so that an angle is formed between the pump light and the seed light, thereby exciting high-order modes to increase the output power and output fundamental mode spot.

Description

Technical Field

[0001] The present invention relates to the field of solid ultrafast lasers, and particularly to a regenerative amplifier and method for increasing the output power by exciting high-order modes in the cavity. Background Art

[0002] As a laser amplifier with many advantages such as high gain, high beam quality, and high stability, the regenerative amplifier has always been the preferred method for people to achieve high-gain laser pulse amplification, and has received extensive attention and in-depth research. In recent decades, the regenerative amplifier has been continuously developing towards higher single-pulse energy and higher average power. As a laser amplifier, the pulse energy output by the regenerative amplifier is limited by the gain and energy storage capacity of the gain medium. The breakthrough in this aspect mainly relies on the development of laser materials and the improvement of pumping technology.

[0003] Currently, the oscillation modes in the cavity of the ytterbium-doped crystal regenerative amplifier reported are all fundamental modes. Usually, the pump light spot size is larger than the signal light and diverges quickly. Therefore, the ability of the regenerative amplifier with fundamental mode oscillation to extract pump light energy is limited. However, if high-order modes are used in the cavity to increase the power of the entire laser, it is impossible to ensure that the output at the output end is fundamental mode output. Summary of the Invention

[0004] The purpose of the present invention is to provide a regenerative amplifier and method for increasing the output power by exciting high-order modes in the cavity, which can increase the output power of the regenerative amplifier by exciting high-order modes and ensure that the output light of the regenerative amplifier is fundamental mode.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A regenerative amplifier for increasing the output power by exciting high-order modes in the cavity, comprising a ytterbium-doped fiber oscillator, a pulse stretcher, a crystal regenerative amplifier module, and a pulse compressor arranged in the optical path sequence direction;

[0007] The ytterbium-doped fiber oscillator is used to generate an initial laser pulse;

[0008] The pulse stretcher is used to stretch the initial laser pulse;

[0009] The crystal regenerative amplifier is used to excite high-order modes to amplify the laser pulse;

[0010] The pulse compressor is used to compress the amplified laser pulse;

[0011] The crystal regenerative amplifier sequentially includes a polarization beam splitter PBS2, a Faraday rotator FR, a half-wave plate HWP, and a polarization beam splitter PBS1 in the optical path sequence; after the polarization beam splitter PBS1 splits the light, it sequentially passes through a quarter-wave plate QWP, a Pockels cell PC, and a first resonant cavity end mirror EM1 in the optical path sequence; after being reflected by the first resonant cavity end mirror EM1, it sequentially passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, a 45° mirror HR1, a first concave mirror CM1, a first dichroic mirror DM, a laser crystal, a second dichroic mirror DM, a second concave mirror CM2, and a second resonant cavity end mirror EM2 in the optical path sequence; it further includes a laser diode LD for generating pump light, and the pump light passes through a second convex lens L2 and is reflected by a 45° mirror HR2 and a mirror HR3 and then focused into the laser crystal from the right side of the laser crystal through a convex lens L1; the mirror HR3 is provided with a knob, and the angle of the mirror HR3 is adjusted through the knob so that the pump light generates an offset of 100 - 300 microns in the crystal.

[0012] Further, the laser crystal is a Yb:CaAlGdO4 laser crystal, and the doping concentration of Yb ions is 2 wt%; the size of the crystal is 3×3×8 mm. The spot size of the initial laser pulse in the laser crystal is 400 - 500 microns, and the spot size of the pump light in the laser crystal is 600 - 800 microns.

[0013] A method for using a regenerative amplifier for improving the output power by intracavity exciting high-order modes, based on the regenerative amplifier for improving the output power by intracavity exciting high-order modes, includes the following steps:

[0014] S1: Using a ytterbium-doped fiber laser to generate an initial laser pulse, and the initial laser pulse enters the crystal regenerative amplifier after being broadened by a pulse stretcher.

[0015] S2: Using the crystal regenerative amplifier to form an angle between the pump light and the initial laser pulse, exciting high-order modes to amplify the laser pulse, and improving the power of the laser pulse.

[0016] S3: Using a pulse compressor to compress the amplified laser pulse and then output it.

[0017] Further, in step S2, the initial laser pulse sequentially passes through a polarization beam splitter PBS2, a Faraday rotator FR, a half-wave plate HWP, and a polarization beam splitter PBS1; after being split by the polarization beam splitter PBS1, it sequentially passes through a quarter-wave plate QWP, a Pockels cell PC, and a first resonator end mirror EM1 in the optical path order; after being reflected by the first resonator end mirror EM1, it sequentially passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, a 45° mirror HR1, a first concave mirror CM1, a first dichroic mirror DM, a laser crystal, a second dichroic mirror DM, a second concave mirror CM2, and a second resonator end mirror EM2 in the optical path order; a pump light is generated by a laser diode LD; the pump light passes through a second convex lens L2 and is reflected by a 45° mirror HR2 and a mirror HR3, and then passes through a first convex lens L1 and is focused into the laser crystal from the right side of the laser crystal; the pump light enters the laser crystal at a small angle with the initial laser pulse to excite high-order modes.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. Provide a regenerative amplifier and method for improving the output power by intracavity excitation of high-order modes, which can improve the extraction of pump light energy, has a high output power, and ensures that the output light is a fundamental mode.

[0020] 2. By using a ytterbium-doped fiber oscillator, a pulse stretcher, a crystal regenerative amplifier module, and a pulse compressor, the initial laser pulse is stretched, amplified, and compressed. The structure is simple and no other components are required, which can improve the single-pulse energy and average power.

[0021] 3. By adjusting the angle of the mirror HR3 with a knob, the pump light and the signal light are angularly offset, exciting high-order modes and significantly improving the output power of the regenerative amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention and do not limit the present invention.

[0023] Figure 1 It is a schematic structural diagram of the present invention.

[0024] Figure 2 It is a schematic diagram of the positions of the seed light A and the pump light B of the present invention before entering the laser crystal.

[0025] Figure 3 It is a schematic diagram of the positions of the seed light A and the pump light B of the present invention after entering the laser crystal.

[0026] Figure 4This is the pattern diagram of the fundamental mode leakage light spot at the 45° mirror HR3 under an output power of 50W in the present invention.

[0027] Figure 5 This is the pattern diagram of the high-order mode leakage light spot at the second resonator end mirror EM2 under an output power of 50W in the present invention.

[0028] Figure 6 This is the output power diagram of the pulse without being compressed by the pulse compressor in the present invention.

[0029] Among them, polarization beam splitter PBS2, Faraday rotator FR, half-wave plate HWP, polarization beam splitter PBS1, quarter-wave plate QWP, Pockels cell PC, first resonator end mirror EM1, 45° mirror HR1, first concave mirror CM1, first dichroic mirror DM, laser crystal, second dichroic mirror DM, second concave mirror CM2, second resonator end mirror EM2, laser diode LD, mirror HR3, first convex lens L1, second convex lens L2, mirror HR3. Detailed implementation manners

[0030] The following further illustrates the present invention through specific embodiments:

[0031] Refer to Figure 1 , a regenerative amplifier for increasing the output power by exciting high-order modes in the cavity, including a ytterbium-doped fiber oscillator, a pulse stretcher, a crystal regenerative amplifier module, and a pulse compressor arranged in the optical path sequence direction;

[0032] The ytterbium-doped fiber oscillator is used to generate initial laser pulses; the ytterbium-doped fiber oscillator is an ultra-wideband ytterbium-doped fiber oscillator, providing seed pulses with a central wavelength of 1020 - 1040nm, a -10dB bandwidth greater than 50nm, and a -3dB bandwidth greater than 30nm, which is a simple broadband seed source.

[0033] The pulse stretcher is used to stretch the initial laser pulses; the seed pulses output from the ultra-wideband ytterbium-doped fiber oscillator are first stretched to 200ps by a Martinez stretcher, and the single diffraction efficiency of the grating in the stretcher at the signal light central wavelength (1020 - 1040nm) is greater than 94%, and the total efficiency is greater than 78%.

[0034] The crystal regenerative amplifier is used to excite high-order modes to amplify the laser pulses;

[0035] The pulse compressor is used to compress the amplified laser pulses;

[0036] The crystal regenerative amplifier sequentially includes a polarization beam splitter PBS2, a Faraday rotator FR, a half-wave plate HWP, and a polarization beam splitter PBS1 in the optical path sequence; after the polarization beam splitter PBS1 splits the light, it sequentially passes through a quarter-wave plate QWP, a Pockels cell PC, and a first resonator end mirror EM1 in the optical path sequence; after being reflected by the first resonator end mirror EM1, it sequentially passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, a 45° reflector HR1, a first concave mirror CM1, a first dichroic mirror DM, a laser crystal, a second dichroic mirror DM, a second concave mirror CM2, and a second resonator end mirror EM2 in the optical path sequence; it further includes a laser diode LD for generating pump light, the pump light passes through a second convex lens L2 and is reflected by a 45° reflector HR2 and a reflector HR3 and then is focused into the laser crystal from the right side of the laser crystal through a first convex lens L1; the reflector HR3 is provided with a knob, and the angle of the reflector HR3 is adjusted by the knob so that the pump light generates an offset of 100-300 microns in the crystal.

[0037] The laser crystal is a Yb:CaAlGdO4 laser crystal, where the doping concentration of Yb ions is 2 wt%; the size of the crystal is 3×3×8 mm. The emission bandwidth of the crystal is 60 nm.

[0038] A method for using a regenerative amplifier to increase the output power by intracavity excitation of higher-order modes, based on the regenerative amplifier for increasing the output power by intracavity excitation of higher-order modes, includes the following steps:

[0039] S1: Use a ytterbium-doped fiber laser to generate an initial laser pulse, and the initial laser pulse enters the crystal regenerative amplifier after being broadened by a pulse stretcher.

[0040] S2: Use the crystal regenerative amplifier to form an angle between the pump light and the initial laser pulse, excite higher-order modes to amplify the laser pulse, and increase the power of the laser pulse.

[0041] S3: Use a pulse compressor to compress the amplified laser pulse and then output it.

[0042] In S2, the initial laser pulse sequentially passes through a polarization beam splitter PBS2, a Faraday rotator FR, a half-wave plate HWP, and a polarization beam splitter PBS1. After being split by the polarization beam splitter PBS1, it sequentially passes through a quarter-wave plate QWP, a Pockels cell PC, and a first resonator end mirror EM1 in the order of the optical path. After being reflected by the first resonator end mirror EM1, it sequentially passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, a 45° mirror HR1, a first concave mirror CM1, a first dichroic mirror DM, a laser crystal, a second dichroic mirror DM, a second concave mirror CM2, and a second resonator end mirror EM2 in the order of the optical path. A pump light is generated by a laser diode LD. The pump light passes through a second convex lens L2, is reflected by a 45° mirror HR2 and a mirror HR3, and then is focused into the laser crystal from the right side of the laser crystal through a first convex lens L1. The pump light enters the laser crystal at a small angle with the initial laser pulse to excite high-order modes. The spot size of the initial laser pulse in the laser crystal is 400 - 500 microns, and the spot size of the pump light in the laser crystal is 600 - 800 microns. Exciting high-order modes can increase the output power, with the maximum increase up to 50W.

[0043] The initial laser pulse becomes horizontally polarized light after passing through the Faraday rotator FR and the half-wave plate HWP, enters the laser resonator through the polarization beam splitter PBS2. The range of the laser resonator is from the end mirror EM1 to EM2. Starting from EM1, it sequentially passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, the 45° mirror HR1, the concave mirror CM1, the dichroic mirror DM, the laser crystal Yb:Calgo, the dichroic mirror DM, and the end mirror EM2. The total cavity length is 2 meters, and the polarization of the initial laser pulse in the cavity is vertically polarized. After the pulse is amplified by traveling back and forth in the cavity several times, by applying different voltages to the Pockels cell PC, the polarization direction of the pulse becomes horizontally polarized after passing through the quarter-wave plate QWP and the Pockels cell PC, and transmits through the polarization beam splitter PBS1. At this time, the beam transmission direction is opposite to that when the initial laser pulse beam enters. After passing through the half-wave plate HWP and the Faraday rotator FR again, the polarization direction is vertically polarized. After being reflected by the polarization beam splitter PBS2, the amplified pulse is output. A power meter is placed in front of the pulse compressor to measure the power of the output pulse, and then it enters the next-stage pulse compressor for compression.

[0044] Taking the dichroic mirror DM, the laser crystal, and the dichroic mirror DM as the dividing line, the regenerative cavity is divided into an upper part and a lower part. The upper part can use a CCD to observe the light leakage spots after the end mirror EM2 and the concave mirror CM2, and the lower part can use a CCD to observe the light leakage spots after the concave mirror CM1 and the 45° mirror HR3. At this time, the light leakage spots observed after the end mirror EM2 and the concave mirror CM2 in the upper part are high-order modes, and the light leakage spots observed after the concave mirror CM1 and the 45° mirror HR3 in the lower part are fundamental modes.

[0045] Figure 2 The seed light A and the pump light B do not completely overlap. Rotate HR3 to offset the pump light, forming a small angle between the seed light A and the pump light B. As Figure 2 shown, before the pump light B enters the crystal, in the CCD, the pump light B is located at the lower right of the seed light A. In practice, the pump light B is located at the lower right of the seed light A. As Figure 3 shown, the pump light B is located at the upper right of the seed light A. In practice, the pump light B is located at the lower left of the seed light A. The pump light B obliquely enters the crystal from right to left at a small angle.

[0046] Refer to Figures 4 - 5 , the pump light obliquely enters the crystal to excite the high-order mode, and the leakage light spot at the second resonant cavity end mirror EM2 is observed to be a high-order mode spot. However, the output of the leakage light spot observed at the 45° mirror HR3 is a fundamental mode spot.

[0047] Refer to Figure 6 , as the pump power starts to increase, the output power is 0. When the pump power increases to 150 W, an output power of 0.5 W starts to be measured. When the pump power increases from 150 W to 215 W, the output power gradually increases from 0.5 W to 22.5 W. When the pump power increases from 215 W to 235 W, the output power does not increase significantly, and the seed light is amplified to saturation. However, when the pump power increases from 235 W to 245 W, the high-order mode is excited, and the output power increases significantly, jumping from 22.5 W to 27.5 W. When the pump power increases from 245 W to 280 W, the output power gradually increases from 27.5 W to 37 W. When the pump power increases from 280 W to 330 W, the output power decreases from 37 W to 35.5 W, and the seed light amplification reaches saturation. Then, when the pump power increases from 330 W to 340 W, another high-order mode is excited, and the output power increases significantly, jumping from 35.5 W to 48 W. When the pump power increases from 340 W to 355 W, the output power increases to 49.5 W, and then the seed light amplification reaches saturation.

Claims

1. A regenerative amplifier for increasing output power by exciting high-order modes within a cavity, characterized in that: It includes an ytterbium-doped fiber oscillator, a pulse stretcher, a crystal regenerative amplifier module, and a pulse compressor arranged in the order of the optical path; An ytterbium-doped fiber oscillator is used to generate the initial laser pulse; The pulse stretcher is used to stretch the initial laser pulse; Crystal regenerative amplifiers are used to excite high-order modes to amplify laser pulses; The pulse compressor is used to compress the amplified laser pulse; The crystal regenerative amplifier includes a polarization beam splitter PBS2, a Faraday rotator FR, a half-wave plate HWP, and a polarization beam splitter PBS1 in order of the optical path; after the polarization beam splitter PBS1 splits the light, the light passes through a quarter-wave plate QWP, a Pockels cell PC, and a first resonant cavity end mirror EM1 in order of the optical path; after being reflected by the first resonant cavity end mirror EM1, the light passes through a Pockels cell PC, a quarter-wave plate QWP, a polarization beam splitter PBS1, a 45° reflector HR1, a first concave mirror CM1, a first dichroic mirror DM, a laser crystal, a second dichroic mirror DM, a second concave mirror CM2, and a second resonant cavity end mirror EM2 in order of the optical path; the crystal regenerative amplifier also includes a laser diode LD for generating pump light, the pump light passes through a second convex lens L2, is reflected by a 45° reflector HR2 and a reflector HR3, and is focused into the laser crystal from the right side of the laser crystal through the first convex lens L1; the reflector HR3 is provided with a knob, and the angle of the reflector HR3 is adjusted by the knob so that the pump light generates a displacement of 100-300 microns in the crystal.

2. A regenerative amplifier for increasing output power by exciting high-order modes in a cavity according to claim 1, characterized in that: The laser crystal is a Yb:CaAlGdO4 laser crystal, wherein the doping concentration of Yb ions is 2wt%; the size of the crystal is 3×3×8mm.

3. A regenerative amplifier for increasing output power by exciting high-order modes in a cavity according to claim 2, characterized in that: The spot size of the initial laser pulse in the laser crystal is 400-500 microns, and the spot size of the pump light in the laser crystal is 600-800 microns.

4. A method for using a regenerative amplifier for increasing output power by exciting a high-order mode in a cavity, based on the regenerative amplifier for increasing output power by exciting a high-order mode in a cavity as claimed in claim 3, characterized in that: The following steps are involved: S1: using an ytterbium-doped fiber laser to generate an initial laser pulse, the initial laser pulse is stretched by a pulse stretcher and then enters a crystal regenerative amplifier; S2: Using a crystal regenerative amplifier to form an angle between the pump light and the initial laser pulse, excite a high-order mode to amplify the laser pulse, and increase the power of the laser pulse; S3: Use a pulse compressor to compress the amplified laser pulse and then output it.

5. The method for using a regenerative amplifier for increasing output power by exciting a high-order mode in a cavity according to claim 4, characterized in that: In the S2, the initial laser pulse passes through the polarization beam splitter PBS2, the Faraday rotator FR, the half-wave plate HWP, and the polarization beam splitter PBS1 in sequence; after being split by the polarization beam splitter PBS1, the laser pulse passes through the quarter-wave plate QWP, the Pockels cell PC, and the first resonant cavity end mirror EM1 in sequence according to the optical path sequence; after being reflected by the first resonant cavity end mirror EM1, the laser pulse passes through the Pockels cell PC, the quarter-wave plate QWP, the polarization beam splitter PBS1, the 45° reflector HR1, the first concave mirror CM1, the first dichroic mirror DM, the laser crystal, the second dichroic mirror DM, the second concave mirror CM2, and the second resonant cavity end mirror EM2 in sequence according to the optical path sequence; the laser diode LD is used to generate pump light; the pump light passes through the second convex lens L2, is reflected by the 45° reflector HR2 and the reflector HR3, and is focused into the laser crystal from the right side of the laser crystal through the first convex lens L1; the pump light enters the laser crystal at a small angle with the initial laser pulse to excite a high-order mode.

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