Yb-based high-power pulse slice laser with adjustable pulse width

Abstract

The invention relates to the technical field of slice lasers, in particular to a Yb-based high-power pulse slice laser with an adjustable pulse width. Comprising a pumping source, a multi-pass pumping module and a resonant cavity which are sequentially arranged along a light path, and the resonant cavity is composed of a first end mirror, a thin-sheet crystal, a thin-film polaroid, a quarter-wave plate, an electro-optical switch and a second end mirror according to the light path sequence. The slice crystal serves as a gain medium and is used for pumping pump light and generating a laser beam; the thin film polarizer highly transmits horizontal polarized light and highly reflects vertical polarized light and is used for outputting laser in the cavity, the quarter-wave plate and the electro-optical switch are used for controlling loss in the cavity so as to output nanosecond pulses, and the plane mirror is used as a resonant cavity end mirror. The pulse width output by the slice laser can be effectively regulated and controlled, the regulation range reaches ten to hundreds of nanoseconds, and the power output by the laser does not change along with the change of the pulse width.

Description

Technical Field

[0001] The invention relates to the technical field of thin-slice lasers, and in particular to a high-power pulse thin-slice laser with adjustable pulse width based on Yb. Background Art

[0002] High-power laser diode-pumped Q-switched nanosecond solid-state lasers have important applications in industrial processing, biomedicine, remote sensing, etc. In these applications, the width of nanosecond pulses often has an important impact. For example, the detection distance of scanning imaging lidar is inversely proportional to the pulse width, the optimal processing rate of different materials corresponds to different pulse widths, and nanosecond pulses of different widths are usually required for material damage testing. Compared with using multiple lasers, using Q-switched nanosecond solid-state lasers with adjustable pulse width can greatly reduce system complexity and cost.

[0003] The pulse width output by the current laser diode pumped Q-switched nanosecond solid-state laser is usually a fixed value; a few lasers with adjustable pulse width are generally adjusted by changing the high-voltage signal of the electro-optical switch, and their adjustment range is only within the range of 10-100ns, and their output power will be greatly attenuated with the change of pulse width. The gain medium used in these laser diode pumped Q-switched nanosecond solid-state lasers is a bulk crystal, and the thermal lens effect is more significant, making it difficult to achieve high-power operation; while the gain medium used in the thin-slice laser is only on the order of 100-300μm, and the temperature gradient is approximately one-dimensional along the axial direction. Compared with the traditional bulk gain medium crystal, the thin-slice laser has a smaller thermal lens effect while bearing a higher pump power density, and can achieve high-power, high-stability, and high-beam quality laser output. In the electro-optical Q-switched laser based on the thin-slice gain medium, by rotating the quarter-wave plate and the electro-optical crystal, it is possible to achieve a wide range of pulse width adjustment while maintaining high power and high stability output. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a Yb-based high-power pulse thin-disk laser with adjustable pulse width, which can achieve wide range of pulse width adjustment of 10-400ns and maintain high-power and high-stability output during the adjustment process.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: a high-power pulse thin-slice laser with adjustable pulse width based on Yb, comprising: a pump source, a multi-pass pump module and a resonant cavity arranged in sequence along an optical path;

[0006] A first end mirror, a thin film polarizer, a quarter-wave plate, an electro-optic switch, and a second end mirror are provided in the resonant cavity; the first end mirror, the thin crystal in the multi-pass pumping module, and the thin film polarizer are arranged in the optical path sequence, and the thin film polarizer, the quarter-wave plate, the electro-optic switch, and the second end mirror are arranged in sequence along the optical path; the resonant cavity is used to provide a round-trip optical path and form oscillating laser;

[0007] The pump light emitted by the pump source is focused on the thin crystal located in the resonant cavity multiple times through the multi-pass pumping module to achieve efficient absorption of the pump light.

[0008] The thickness of the thin crystal is 50 - 200 μm.

[0009] The matrix material of the thin crystal is one of YAG, LuAG, Lu2O3, and CALGO.

[0010] The thin film polarizer is used to transmit horizontally polarized light, reflect vertically polarized light, and output horizontally polarized light.

[0011] A quarter-wave plate and an electro-optic switch are provided between the thin film polarizer and the second end mirror; when the electro-optic switch is closed, there is no oscillating light in the cavity; after the electro-optic switch is turned on, the vertically polarized oscillating light emitted by the thin crystal is reflected by the thin film polarizer, passes through the quarter-wave plate and the electro-optic switch for the first time, and then passes through the quarter-wave plate and the electro-optic switch again after being reflected by the second end mirror, and a part of it is converted into horizontally polarized light and output through the thin film polarizer.

[0012] The quarter-wave plate and the electro-optic switch are respectively installed on two rotating brackets, the rotation axes of the rotating brackets coincide with the axes of the quarter-wave plate or the electro-optic switch, and the rotation angles are respectively controlled by two motors;

[0013] By adjusting the rotation angles of the quarter-wave plate and the electro-optic switch, the output coupling rate of the thin film polarizer is changed to achieve a large-range adjustment of the output pulse width.

[0014] The output high-voltage signal of the electro-optic switch is a square wave, the rising edge and the falling edge of the square wave are less than 7 ns, and the repetition frequency is adjustable from 1 kHz to 100 kHz to achieve the adjustment of the output pulse repetition frequency.

[0015] A method for adjusting the pulse width of a high-power pulsed thin disk laser based on Yb with adjustable pulse width includes the following steps:

[0016] The pump light emitted by the pump source enters the resonant cavity through the multi-pass pumping module;

[0017] When the electro-optic switch is closed, there is no oscillating light in the resonant cavity;

[0018] After the electro - optical switch is turned on, the oscillating light in the resonant cavity is reflected by the first end - mirror and focused on the thin - film crystal. The vertically polarized oscillating light emitted by the thin - film crystal is reflected by the thin - film polarizer and then passes through the quarter - wave plate and the electro - optical switch for the first time. After being reflected by the second end - mirror, it passes through the quarter - wave plate and the electro - optical switch again, and part of it is converted into horizontally polarized light and output through the thin - film polarizer.

[0019] By controlling the rotation angles of the quarter - wave plate and the electro - optical switch to adjust the output coupling rate of the resonant cavity, the following steps are included:

[0020] T on is the output coupling rate of the resonant cavity when the electro - optical switch is turned on, and T off is the output coupling rate of the resonant cavity when the electro - optical switch is turned off; θ1 is the rotation angle of the quarter - wave plate relative to the initial position, and θ2 is the rotation angle of the electro - optical switch relative to the initial position; the initial position is the position where the fast and slow axes of the quarter - wave plate or the electro - optical switch make an angle of 45° with the horizontal direction.

[0021] T on =sin 2 (2θ2)sin 2 2(θ2 - θ1)

[0022] T off =cos 2 (2θ2)

[0023] When θ1 and θ2 are equal to 0°, the relationship between the output pulse width τ0 and the resonant - cavity length L is: τ0 = 2L / c, where c is the speed of light in vacuum.

[0024] By controlling the rotation angles of the quarter - wave plate and the electro - optical switch to adjust the output coupling rate of the resonant cavity, multiple working modes are realized:

[0025] Mode 1: The rotation angle θ1 of the quarter - wave plate and the rotation angle θ2 of the electro - optical switch are equal. θ1 and θ2 increase from 0° to 32.5°, and the output pulse width increases from τ0 to 25τ0.

[0026] Mode 2: The rotation angle θ1 of the quarter - wave plate is fixed, and only the rotation angle θ2 of the electro - optical switch is changed, and the absolute value of the difference between θ2 and θ1 is less than 3°, so that the output pulse width is the same as the pulse width output in Mode 1 when the rotation angles are all equal to θ2.

[0027] The present invention has the following beneficial effects and advantages:

[0028] 1. The present invention uses a thin - sheet form as the gain medium for a high - power pulsed laser based on Yb with adjustable pulse width. Since the thickness of the thin - sheet crystal is only a few hundred micrometers, which is much smaller than the thickness of the bulk crystal on the order of 10 mm, its threshold pump power is much greater than that of the bulk crystal. It can achieve a wide range of pulse width adjustment from 10 - 400 ns while maintaining high - power stable laser output.

[0029] 2. The present invention adjusts the pulse width by rotating a quarter - wave plate and an electro - optic crystal. The adjustment method is simple and efficient. And the rotation angle is controlled by a stepper motor, with precise angle adjustment and good repeatability. Brief Description of the Drawings

[0030] Figure 1 It is a schematic structural diagram of a high - power pulsed thin - sheet laser based on Yb with adjustable pulse width in an embodiment of the present invention.

[0031] In the figure: 1 is a pump source, 2 is a multi - pass pump module, 3 is a resonant cavity, 4 is a first end mirror, 5 is a thin - sheet crystal, 6 is a thin - film polarizer, 7 is a quarter - wave plate, 8 is an electro - optic switch, and 9 is a second end mirror. Detailed Embodiments

[0032] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail below with reference to the drawings and specific embodiments.

[0033] A high - power pulsed thin - sheet laser based on Yb with adjustable pulse width includes a pump source, a multi - pass pump module, and a resonant cavity arranged in sequence along the optical path. The pump light emitted by the pump source is focused on the thin - sheet crystal multiple times through the multi - pass pump module to achieve efficient absorption of the pump light. The resonant cavity includes a thin - sheet crystal and multiple optical elements, which are used to provide a round - trip optical path and form oscillating laser light in the resonant cavity.

[0034] The thickness of the thin - sheet crystal is 50 - 200 μm, and the matrix material is one of YAG, LuAG, Lu2O3, or CALGO.

[0035] The resonant cavity has two end mirrors with high reflectivity for the oscillating laser, namely the first end mirror and the second end mirror.

[0036] The resonant cavity has a thin - film polarizer between the thin - sheet crystal and the second end mirror, which is highly transmissive to horizontally polarized light and highly reflective to vertically polarized light, and is used to output horizontally polarized light from the cavity.

[0037] The resonant cavity has a quarter-wave plate and an electro-optic switch between the thin-film polarizer and the second end mirror. When the electro-optic switch is closed, the resonant cavity has a low Q value and there is no oscillating light in the cavity. After the electro-optic switch is turned on, the resonant cavity has a high Q value. The vertically polarized oscillating light emitted by the thin crystal, after being reflected by the thin-film polarizer, passes through the quarter-wave plate and the electro-optic switch for the first time, and then passes through the quarter-wave plate and the electro-optic switch again after being reflected by the second end mirror. A certain proportion is converted into horizontally polarized light and output through the thin-film polarizer.

[0038] The quarter-wave plate and the electro-optic switch are installed on a rotating bracket controlled by a stepper motor. By adjusting the rotation angles of the quarter-wave plate and the electro-optic switch, the output coupling rate of the thin-film polarizer is changed, and a large-range adjustment of the output pulse width is realized.

[0039] The electro-optic crystal material of the electro-optic switch is one of barium metaborate (BBO), lithium triborate (LBO), or potassium titanyl phosphate (KTP).

[0040] The output high-voltage signal of the electro-optic switch is a square wave. The rising edge and falling edge of the square wave are less than 7 ns, and the repetition frequency is adjustable from 1 kHz to 100 kHz, realizing the adjustment of the output pulse repetition frequency.

[0041] As Figure 1 shown, a high-power pulsed thin disk laser based on Yb with adjustable pulse width provided by the present invention includes a pump source 1, a multi-pass pumping module 2, and a resonant cavity 3 arranged in sequence along the optical path. The pump light emitted by the pump source 1 is focused on the thin crystal 4 multiple times through the multi-pass pumping module to achieve efficient absorption of the pump light. The resonant cavity 3 is composed of a first end mirror 4, a thin crystal 5, a thin-film polarizer 6, a quarter-wave plate 7, an electro-optic switch 8, and a second end mirror 9 in the order of the optical path.

[0042] In an embodiment of the present invention, an antireflection film is coated on the front side of the thin crystal 5, and a reflection film is coated on the rear side. The antireflection film is used to improve the transmittance of the pump light, and the reflection film is used to improve the reflectivity of the remaining pump light. Specifically, the thin crystal 5 uses Yb as the gain medium, and its thickness range is 100 - 300 μm.

[0043] In an embodiment of the present invention, the pump source 1 uses a laser diode with a wavelength of 940 or 969 nm. The pump light is focused on the thin crystal 5 multiple times through the multi-pass pumping module, and its absorption efficiency for the pump light exceeds 98%.

[0044] In an embodiment of the present invention, the two end mirrors of the resonant cavity 3, the first end mirror 4 and the second end mirror 5, have high reflectivity for the oscillating laser, and their radius of curvature is in the range of 1 m - ∞. By changing the radius of curvature of the first end mirror 4 and the second end mirror 5, it can be ensured that the mode radius on the thin crystal accounts for 80% - 90% of the pump spot radius, and the laser output from the resonant cavity is the fundamental transverse mode.

[0045] In an embodiment of the present invention, when the electro-optical switch 8 is turned on, the resonant cavity 3 is in a high Q value state, and the output coupling ratio T on is approximately zero. The laser only oscillates and amplifies within the resonant cavity 3 without output. The high reflection characteristic of the thin-film polarizer 6 for vertically polarized light ensures that the polarization state of the oscillating laser within the resonant cavity 4 is in the vertical direction. At the moment when the electro-optical switch 8 is turned off, the output coupling ratio of the resonant cavity 3 is T off , and the oscillating light within the resonant cavity 4 is reflected by the second end mirror 9 and then output from the thin-film polarizer 6 at this output coupling ratio.

[0046] In an embodiment of the present invention, T on and T off are determined by the rotation angles θ1 and θ2 of the quarter-wave plate 7 and the electro-optical switch 8 relative to their initial positions. The initial position is defined as the position where the fast and slow axes of the quarter-wave plate 7 and the electro-optical switch 8 form an angle of 45° with the horizontal direction. The formula for T on in terms of θ1 and θ2 is expressed as: T on =sin 2 (2θ2)sin 2 2(θ2 - θ1), and the formula for T off in terms of θ2 is expressed as: T off =cos 2 (2θ2). When θ1 and θ2 are equal to 0°, the relationship between the output pulse width τ0 and the resonant cavity length L is: τ0 = 2L / c, where c is the speed of light in vacuum.

[0047] In an embodiment of the present invention, the resonant cavity 3 can be in two working modes. The first is that the rotation angles θ1 and θ2 of the quarter-wave plate 7 and the electro-optical switch 8 are equal. As θ1 and θ2 increase from 0° to 32.5°, the output pulse width will increase from τ0 to 25τ0. The second is to fix θ1 and only change θ2, and the absolute value of the difference between θ2 and θ1 is less than 3°. The output pulse width in this mode is the same as the pulse width output in the first mode when the rotation angle is equal to θ2. However, since only the angle θ2 of the electro-optical switch 8 needs to be adjusted, it is more convenient to use when the adjustment range is not large.

[0048] In an embodiment of the present invention, the rotation angles of the quarter-wave plate 7 and the electro-optical switch 8 are both controlled by a stepping motor with a precision of 0.05°, a maximum rotation speed of 10° / s, and a minimum rotation speed of 0.05° / s. The angle adjustment is fast, accurate, and has good repeatability.

[0049] In an embodiment of the present invention, the electro-optical crystal material used for the electro-optical switch 8 is barium metaborate (BBO), lithium triborate (LBO), or potassium titanyl phosphate (KTP).

[0050] In an embodiment of the present invention, the output high-voltage signal of the electro-optical switch 8 is a square wave, the rise and fall edges of the square wave are less than 7 ns, and the repetition frequency is adjustable from 1 kHz to 100 kHz, so as to realize the adjustment of the output pulse repetition frequency.

[0051] The present invention utilizes the technology of combining an electro-optical Q-switched laser based on a thin-sheet gain medium with a rotating quarter-wave plate and an electro-optical switch to adjust the pulse width, and realizes the output of high-power nanosecond lasers with continuously adjustable pulse widths. Since the thickness of the thin-sheet crystal 2 is only 100 - 300 μm, the threshold pump power is relatively high, and its heat conduction direction only transmits along the axial direction, with less thermal effect, which solves the technical problems that the output power of a laser with adjustable pulse width based on a bulk gain medium is low, and the output efficiency decreases significantly as the pulse width increases. This laser can meet the requirements of high-power nanosecond lasers with continuously adjustable pulse widths in fields such as industrial processing, biomedicine, and remote sensing detection.

[0052] The above are only the embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, expansions, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A high-power pulsed thin-disk laser based on Yb with adjustable pulse width, characterized in that, Including: A pump source (1), a multi-pass pump module (2), and a resonator (3) arranged in sequence along the optical path; A first end mirror (4), a thin-film polarizer (6), a quarter-wave plate (7), an electro-optic switch (8), and a second end mirror (9) are provided in the resonator (3); the first end mirror (4), the thin crystal (5) in the multi-pass pump module (2), and the thin-film polarizer (6) are arranged in the order of the optical path, and the thin-film polarizer (6), the quarter-wave plate (7), the electro-optic switch (8), and the second end mirror (9) are arranged in sequence along the optical path; the resonator (3) is used to provide a round-trip optical path and form oscillating laser; The pump light emitted by the pump source (1) is focused on the thin crystal (5) located in the resonator (3) multiple times through the multi-pass pump module (2) to achieve efficient absorption of the pump light.

2. The high-power pulsed thin-disk laser based on Yb with adjustable pulse width according to claim 1, wherein The thickness of the thin crystal (5) is 50 - 200 μm.

3. A high-power pulsed thin-disk laser based on Yb with adjustable pulse width according to claim 1, characterized in that, The matrix material of the thin crystal (5) is one of YAG, LuAG, Lu2O3, and CALGO.

4. A high-power pulsed thin-disk laser based on Yb with adjustable pulse width according to claim 1, characterized in that, The thin-film polarizer (6) is used to transmit horizontally polarized light, reflect vertically polarized light, and output horizontally polarized light.

5. A high-power pulsed thin disk laser based on Yb with adjustable pulse width according to claim 1, characterized in that, A quarter-wave plate (7) and an electro-optic switch (8) are provided between the thin-film polarizer (6) and the second end mirror (9); when the electro-optic switch (8) is closed, there is no oscillating light in the cavity; after the electro-optic switch (8) is turned on, the vertically polarized oscillating light emitted by the thin crystal (5) is reflected by the thin-film polarizer (6), passes through the quarter-wave plate (7) and the electro-optic switch (8) for the first time, and after being reflected by the second end mirror (9), passes through the quarter-wave plate (7) and the electro-optic switch (8) again, and a part is converted into horizontally polarized light and output through the thin-film polarizer (6).

6. A high-power pulsed thin disk laser based on Yb with adjustable pulse width according to claim 1, characterized in that, The quarter-wave plate (7) and the electro-optic switch (8) are respectively installed on two rotating brackets, the rotation axes of the rotating brackets coincide with the axes of the quarter-wave plate (7) or the electro-optic switch (8), and the rotation angles are respectively controlled by two motors; By adjusting the rotation angles of the quarter-wave plate (7) and the electro-optic switch (8), the output coupling ratio of the thin-film polarizer (6) is changed to achieve a wide range of adjustment of the output pulse width.

7. A high-power pulsed thin-disk laser based on Yb with adjustable pulse width according to claim 1, characterized in that The output high-voltage signal of the electro-optic switch (8) is a square wave, the rising edge and the falling edge of the square wave are less than 7 ns, and the repetition frequency is adjustable from 1 kHz to 100 kHz to achieve the adjustment of the output pulse repetition frequency.

8. A pulse width adjustment method for a high-power pulsed thin disk laser based on Yb with adjustable pulse width, characterized in that, Including the following steps: The pump light emitted by the pump source (1) enters the resonator (3) through the multi-pass pump module (2); When the electro-optic switch (8) is closed, there is no oscillating light in the resonator (3); After the electro-optic switch (8) is turned on, the oscillating light in the resonator (3) is reflected by the first end mirror (4) and focused on the thin crystal (5), and the vertically polarized oscillating light emitted by the thin crystal (5) is reflected by the thin-film polarizer (6), passes through the quarter-wave plate (7) and the electro-optic switch (8) for the first time, and after being reflected by the second end mirror (9), passes through the quarter-wave plate (7) and the electro-optic switch (8) again, and a part is converted into horizontally polarized light and output through the thin-film polarizer (6).

9. A pulse width adjustment method for a high-power pulsed thin disk laser with adjustable pulse width based on Yb according to claim 8, characterized in that, By controlling the rotation angles of the quarter-wave plate (7) and the electro-optical switch (8), the output coupling rate of the resonant cavity (3) is adjusted, including the following steps: T on is the output coupling rate of the resonant cavity (3) when the electro-optical switch (8) is turned on, T off is the output coupling rate of the resonant cavity (3) when the electro-optical switch (8) is turned off; θ1 is the rotation angle of the quarter-wave plate (7) relative to the initial position, and θ2 is the rotation angle of the electro-optical switch (8) relative to the initial position; the initial position is the position where the fast and slow axes of the quarter-wave plate (7) or the electro-optical switch (8) form an angle of 45° with the horizontal direction; T on = sin 2 (2θ2)sin 2 2(θ2 - θ1) T off = cos 2 (2θ2) When θ1 and θ2 are equal to 0°, the relationship between the output pulse width τ0 and the cavity length L of the resonant cavity is: τ0 = 2L / c, where c is the speed of light in vacuum.

10. A pulse width adjustment method for a high-power pulsed thin disk laser with adjustable pulse width based on Yb according to claim 9, characterized in that, By controlling the rotation angles of the quarter-wave plate (7) and the electro-optical switch (8), the output coupling rate of the resonant cavity (3) is adjusted to achieve multiple working modes: Mode 1: The rotation angle θ1 of the quarter-wave plate (7) is equal to the rotation angle θ2 of the electro-optical switch (8). As θ1 and θ2 increase from 0° to 32.5°, the output pulse width increases from τ0 to 25τ0. Mode 2: The rotation angle θ1 of the quarter-wave plate (7) is fixed, and only the rotation angle θ2 of the electro-optical switch (8) is changed, and the absolute value of the difference between θ2 and θ1 is less than 3°, so that the output pulse width is the same as the pulse width output in Mode 1 when the rotation angles are all equal to θ2.

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