Apparatus and method for nonlinear frequency conversion regenerative amplification

Abstract

The application discloses a device and a method for nonlinear frequency conversion regenerative amplification, and belongs to the technical field of laser nonlinear frequency conversion. The device comprises a signal light injection unit, a regenerative amplification cavity unit and a pump light synchronization unit. The regenerative amplification cavity unit comprises an optical resonant cavity structure module, a polarization control module and a nonlinear action module. The polarization control module is driven by a time sequence controller to form a time domain switch, and the signal light is accurately controlled to circulate in the cavity for a preset number of times. At the same time, the pump light synchronization unit generates a pump pulse train laser which is synchronized with the circulation process and whose sub-pulse power increases in sequence, so that the signal light occurs optical parametric amplification with a corresponding pump sub-pulse in a nonlinear crystal in each circulation. The application converts the spatial complexity of multi-stage amplification into time domain controllability, realizes high-efficiency and high-gain nonlinear frequency conversion by using a single-stage compact structure, and significantly improves the system integration and stability.

Description

A nonlinear frequency conversion regenerative amplification device and method thereof Technical Field

[0001] This application relates to the field of laser nonlinear frequency conversion technology, and more specifically to a device and method for nonlinear frequency conversion regenerative amplification. Background Technology

[0002] High-repetition-rate, high-energy ultrafast lasers have a wide range of applications in advanced medical equipment, laser micro-nano fabrication, and other fields. However, due to material limitations, the technology for directly generating lasers in the visible and mid-infrared bands is still immature. Currently, the main techniques used are based on nonlinear frequency conversion methods, including optical parametric amplification and optical parametric oscillation.

[0003] Current technologies involve passing the laser through a nonlinear crystal in a single pass or allowing the light to oscillate back and forth within a cavity. For short pulses at the picosecond or even femtosecond level, the gain of a single conversion is limited, often requiring the optical path to be connected in multiple stages, each equipped with a crystal, temperature control, and synchronization device. This results in large size, numerous components, and long debugging cycles, and even slight vibrations or temperature drifts in the field can cause significant output jitter.

[0004] Another approach is to circulate the signal light multiple times within the cavity, gaining a small gain each time it passes through the crystal. However, a simple and reliable timing control method has been lacking. The crystal is also sensitive to high peak power; excessive power can cause a reverse conversion, reverting the generated signal back to its original state, resulting in a decrease in output power instead of an increase. Simultaneously, the heat generated during continuous operation alters the crystal temperature, causing a gradual shift in the optimal wavelength and a subsequent drop in efficiency. Maintaining stability requires complex heat dissipation and real-time compensation, further increasing the system load.

[0005] Therefore, there is an urgent need for a nonlinear frequency conversion regenerative amplification device and method that allows the same signal light to be amplified multiple times in the same crystal without increasing the number of crystals or extending the spatial optical path, and can suppress reverse conversion and thermal drift in real time, thereby obtaining a new wavelength output with high energy and high stability, while meeting the needs of equipment miniaturization and long-term reliable operation in industrial fields. Summary of the Invention

[0006] The purpose of this application is to provide a nonlinear frequency conversion regenerative amplification device and method, which can solve at least one of the aforementioned technical problems. The specific solution is as follows:

[0007] A nonlinear frequency conversion regenerative amplification device includes: a signal light injection unit, a regenerative amplification cavity unit, and a pump light synchronization unit;

[0008] The signal light injection unit is used to inject linearly polarized signal light into the regenerative amplification cavity unit;

[0009] The regenerative amplification cavity unit includes an optical resonant cavity structure module, a polarization control module, and a nonlinear action module.

[0010] The optical resonant cavity structure module includes at least one polarizing beam splitter, a beam combiner, and at least one reflecting mirror. The polarizing beam splitter, the beam combiner, and the reflecting mirror together constitute an optical resonant cavity for the round-trip propagation of the signal light.

[0011] The polarization control module includes an electro-optic modulator, which is disposed in the optical resonant cavity. It is used to change the polarization state of the signal light so that the signal light circulates back and forth in the optical resonant cavity a preset number of times before being output through the polarization beam splitter.

[0012] The nonlinear action module includes a nonlinear crystal disposed within the optical resonant cavity structure module;

[0013] The pump light synchronization unit is used to generate pump pulse train laser. The pump pulse train laser is synchronized with the cyclic process of the signal light, so that the cyclic signal light and the pump pulse train laser undergo multiple optical parametric amplifications in the nonlinear crystal.

[0014] Furthermore, the optical resonant cavity structure module is a linear standing wave cavity structure;

[0015] The linear standing wave cavity structure includes the polarization beam splitter, the beam combiner, and two high-reflection mirrors, forming a linear standing wave optical path;

[0016] The nonlinear crystal is disposed in the linear standing wave optical path.

[0017] Furthermore, the optical resonant cavity structure module is a ring cavity structure;

[0018] The annular cavity structure includes two polarizing beam splitters, one beam combiner, and one reflecting mirror, forming a unidirectional propagating annular optical path.

[0019] The nonlinear crystal is disposed in the annular optical path.

[0020] Furthermore, the polarizing beam splitter is configured to allow the signal light to enter the optical resonant cavity in a first polarization state, and after the signal light completes a preset number of cycles, to output the signal light from the optical resonant cavity in a second polarization state; the second polarization state is orthogonal to the first polarization state.

[0021] Furthermore, the signal light injection unit includes a seed light source, an optical isolator, and a polarization adjustment element arranged sequentially.

[0022] Furthermore, the electro-optic modulator is a Pockel cell.

[0023] Furthermore, the pump optical synchronization unit includes a pulsed laser source, a timing controller, and an optical delay unit;

[0024] The timing controller is used to synchronize the emission time of the pump pulse train laser with the injection time of the signal light, and to control the peak power of multiple sub-pulses in the pump pulse train laser to be output according to a preset sequence.

[0025] The optical delay device is used to adjust the optical path of the pump pulse train laser, so that each sub-pulse in the pump pulse train laser and the signal light pulse with the corresponding number of cycles in the optical resonant cavity achieve time synchronization and spatial overlap of the light spots when they reach the nonlinear crystal.

[0026] Furthermore, the timing controller is configured to control the peak power of multiple sub-pulses in the pump pulse train laser and output them according to a preset sequence that increases with the number of cycles of the signal light in the optical resonant cavity.

[0027] Furthermore, the optical resonant cavity structure module includes a cavity end mirror;

[0028] The cavity end mirror has high reflectivity to signal light and high transmittance to pump light and idler light generated by optical parametric amplification.

[0029] This application also provides a method for nonlinear frequency conversion regenerative amplification, including:

[0030] The linearly polarized signal light is injected into the optical resonant cavity in the first polarization state;

[0031] The polarization state of the signal light is changed by an electro-optic modulator, causing the signal light to cycle back and forth in the optical resonant cavity a preset number of times.

[0032] During each round trip of the signal light, the signal light and the pump pulse train laser undergo optical parametric amplification in the nonlinear crystal;

[0033] After completing a preset number of cycles, the signal light is output from the optical resonator in a second polarization state orthogonal to the first polarization state.

[0034] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects:

[0035] 1. This application discloses a nonlinear frequency conversion regenerative amplification device and method. The optical resonant cavity structure is designed as a linear standing wave cavity structure. Through a simplified optical path composed of a polarizing beam splitter, a beam combiner, and two high-reflection mirrors, combined with an integrated electro-optic time-domain switch, the signal light is cyclically amplified within the same nonlinear crystal. This condenses the complex system of traditional multi-stage spatial amplification into a compact and easily assembled single cavity. While significantly reducing the number of optical components and improving the long-term stability of the system, it effectively overcomes the efficiency bottleneck of single-pass nonlinear crystal conversion, achieving a total gain close to that of a multi-stage system.

[0036] 2. The nonlinear frequency conversion regenerative amplification device and method of this application, through the unidirectional closed-loop optical path design and the polarization selective reflector in the cavity, makes the signal light circulate along a fixed direction, avoiding the spatial hole burning effect that may be caused by the standing wave field. The design scheme is conducive to obtaining a more stable laser mode, more uniform gain extraction and better thermal management, providing a high-performance and stable implementation path for achieving high beam quality and high average power nonlinear frequency conversion regenerative amplification.

[0037] 3. This application discloses a nonlinear frequency conversion regenerative amplification device and method. Through a timing controller, the co-programmable control of the electro-optic modulator and pump pulse train achieves precise time-domain management of the signal light cycle count, pump sub-pulse synchronization, and power sequence. The method transforms the complex spatial multi-stage amplification process into flexibly programmable steps in the time domain, fundamentally simplifying the system architecture while ensuring the high efficiency and controllability of the energy transfer process. This provides a highly efficient, highly integrated, and extremely flexible general solution for nonlinear frequency conversion of ultrafast lasers. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0039] Figure 1 is a first structural schematic diagram of a nonlinear frequency conversion regenerative amplification device provided in an embodiment of this application.

[0040] Figure 2 is a schematic diagram of the second structure of a nonlinear frequency conversion regenerative amplification device provided in an embodiment of this application.

[0041] Explanation of reference numerals in the attached figures:

[0042] First half-wave plate H1, second half-wave plate H2, third half-wave plate H3, first polarizing beam splitter M, first high-reflection mirror M1, second polarizing beam splitter M2, beam combiner M3, second high-reflection mirror M4, third high-reflection mirror M5, third polarizing beam splitter M6, optical rotator R, quarter-wave plate Q, Pockels cell PC, optical isolator ISO, crystal C, optical retarder TD. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or device that includes that element.

[0045] The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0046] Example 1:

[0047] As shown in Figure 1, this application provides a nonlinear frequency conversion regenerative amplification device, including: a signal light injection unit, a regenerative amplification cavity unit, and a pump light synchronization unit;

[0048] The signal light injection unit is used to inject linearly polarized signal light into the regenerative amplification cavity unit.

[0049] The regenerative amplification cavity unit includes an optical resonant cavity structure module, a polarization control module, and a nonlinear action module.

[0050] The optical resonant cavity structure module includes a polarizing beam splitter, a beam combiner M3, and at least one reflecting mirror. The polarizing beam splitter and one or more reflecting mirrors together constitute an optical resonant cavity for the round-trip propagation of signal light.

[0051] The polarization control module includes an electro-optic modulator, which is set inside the optical resonant cavity. The electro-optic modulator is used to change the polarization state of the signal light, so that the signal light cycles back and forth in the optical resonant cavity a preset number of times before being output through the polarization beam splitter.

[0052] The nonlinear action module includes a nonlinear crystal C disposed within the optical resonant cavity structure module.

[0053] The pump light synchronization unit is used to generate pump pulse train laser. The pump pulse train laser is synchronized with the cyclic process of the signal light, so that the cyclic signal light and the pump pulse train laser undergo multiple optical parametric amplifications in the nonlinear crystal C.

[0054] As shown in Figure 1, the signal light injection unit in this embodiment includes a seed light source, an optical isolator ISO, and a polarization adjustment element arranged sequentially. The polarization adjustment element is a rotator R and / or a half-wave plate. In this embodiment, a polarization adjustment element composed of a rotator R and a second half-wave plate H2 is used. The seed light source generates a linearly polarized signal light λ1 to be amplified. The signal light λ1 has a wavelength of 1568.5 nm, a repetition frequency f2 of 1 kHz, a pulse width of 30 ps, ​​and an initial average power of 10 mW. The rotator R is used to change the polarization state of the injected seed light source and the amplified seed light source output. That is, it realizes the adjustment of the polarization state of the signal light; at the same time, it ensures that the light entering the optical resonant cavity is still a clean first polarization state beam.

[0055] In this embodiment, the regenerative amplification cavity unit includes: an optical resonant cavity structure module, a polarization control module, and a nonlinear action module.

[0056] This application provides a preferred technical solution where the optical resonant cavity structure module is a linear standing wave cavity structure. The linear standing wave cavity structure includes: a second polarizing beam splitter M2, a beam combiner M3, a first high-reflectivity mirror M1 (which serves as a high-reflectivity mirror), and a second high-reflectivity mirror M4. Together, they form a linear standing wave optical path for the round-trip propagation of signal light. In this embodiment, the first high-reflectivity mirror M1 is a 0° high-reflectivity mirror, reflecting the 1568.5 nm wavelength signal light λ1 back along its original path to form a standing wave field. The second polarizing beam splitter M2 is configured to have high transmittance for P-polarized light and high reflectivity for S-polarized light. The beam combiner M3 is a 45° dichroic mirror, with high reflectivity for signal light λ1 and high transmittance for pump light λ3. The second high-reflectivity mirror M4 is a cavity-end mirror. The second high-reflectivity mirror M4 has high reflection of the signal light λ1 and high transmission of the pump light λ3 and the idler light λ2 generated by optical parametric amplification. That is, it has high reflection of the 1568.5nm signal light λ1 and high transmission of the 1030nm pump light λ3 and the idler light λ2 with a wavelength of about 3000nm generated by optical parametric amplification. This eliminates useless interference light, prevents inverse conversion caused by the accumulation of idler light, and ensures the efficiency and stability of nonlinear conversion.

[0057] In this embodiment, the polarization control module includes an electro-optic modulator and a quarter-wave plate Q. The electro-optic modulator is a Pockel cell (PC). The Pockel cell PC is positioned within a linear standing-wave optical path, between the second polarizing beam splitter M2 and the first high-reflection mirror M1. The polarization state of the light passing through the Pockel cell PC is changed by applying a voltage. Initially, the Pockel cell PC has no voltage applied, i.e., zero voltage. P-polarized signal light from the signal light injection unit is injected into the optical resonant cavity through the second polarizing beam splitter M2. In this embodiment, a quarter-wave plate Q is positioned between the Pockel cell PC and the first high-reflection mirror M1. The quarter-wave plate Q is configured in conjunction with the Pockel cell PC. The quarter-wave plate Q acts as a polarization state converter; after light passes through the quarter-wave plate Q twice, the polarization state rotates by 90°. In this embodiment, the time-domain switch formed by the Pockel cell PC, the second polarizing beam splitter M2, and the quarter-wave plate Q controls the signal light to cycle through the optical resonant cavity a preset number of times. In each cycle, the signal light interacts once with a synchronized pump sub-pulse in the nonlinear action module, which is equivalent to the series connection of multiple OPAs.

[0058] This application provides a preferred technical solution in which an optical resonant cavity and a nonlinear action module in the same physical space are multiplexed by multiple actions in a time sequence. Combined with the rapid switching between zero voltage and quarter-wave voltage states by the Pockel cell PC driven by an external timing controller, this combination enables precise conversion of the beam polarization state between 0° and 90°. The principle is that after each two quarter-wave plates Q, the linearly polarized light signal undergoes a 90° rotation in polarization state, changing from P-polarization to S-polarization. When a quarter-wave voltage is applied to the Pockel cell PC, the Pockel cell PC is equivalent to a quarter-wave plate. The second polarizing beam splitter M2, acting as the input and output of the optical resonant cavity structure module, only allows P-polarized light to pass through, maintaining the signal light's polarization state in the optical resonant cavity structure module as S-polarization. The signal light then continuously circulates within the optical resonant cavity structure module. When a zero voltage is applied to the Pockel cell PC... When a voltage is applied, since there is only one quarter-wave plate Q in the optical resonant cavity structure module, the signal light pulse propagates back and forth once between the second polarizing beam splitter M2 and the first high-reflection mirror M1 each time, that is, it passes through the quarter-wave plate Q twice, and the polarization state of the signal light changes once. When a quarter-wave voltage is applied to the Pockel cell PC, the Pockel cell PC is equivalent to a quarter-wave plate. When the signal light traverses back and forth between the second polarizing beam splitter M2 and the first high-reflection mirror M1 once, it passes through the quarter-wave plate Q four times, and the polarization state of the signal light in the optical resonant cavity structure module does not change. When it is necessary to output the amplified signal light, the voltage applied to the Pockel cell PC is changed to zero voltage, and the signal light can be transformed into an output that passes through the second polarizing beam splitter M2 only once.

[0059] To ensure that the signal light circulates within the optical resonant cavity structure module, the timing for switching the voltage of the Pockel cell PC is as follows: after the signal light is reflected by the first high-reflection mirror M1, passes through the quarter-wave plate Q and the Pockel cell PC, and before it is reflected back to the Pockel cell PC by M2, that is, the signal light with polarization state P is injected into the optical resonant cavity structure module through the second polarizing beam splitter M2, passes through the Pockel cell PC and the quarter-wave plate Q, is reflected by the first high-reflection mirror M1 and passes through the quarter-wave plate Q again, changing its polarization state to S. After passing through the Pockel cell PC, a quarter-wave voltage is applied to the Pockel cell PC. The signal light is amplified in a loop within the optical resonant cavity structure module. When output is required, the signal light pulse is reflected by the first high-reflection mirror M1, then passes through the quarter-wave plate Q and the Pockel cell PC, reducing the quarter-wave voltage applied to the Pockel cell PC to zero. The signal light pulse is then reflected again by the second polarizing beam splitter M2, then by the beam combiner M3, the crystal C, and the second high-reflection mirror M4. After passing through the crystal C, beam combiner M3, the second polarizing beam splitter M2, the Pockel cell PC, and the quarter-wave plate Q, it is reflected by the first high-reflection mirror M1 again. After passing through the quarter-wave plate Q, the polarization state changes, and the signal is output from the second polarizing beam splitter M2 after passing through the Pockel cell PC.

[0060] In this embodiment, the nonlinear action module includes a nonlinear crystal C, which is a KTP crystal C, and the nonlinear crystal C is disposed between the beam combiner M3 and the second high-reflection mirror M4.

[0061] In this embodiment, the pump light synchronization unit includes a pulsed laser source, a timing controller, and an optical delay unit (TD). The timing controller synchronizes the emission time of the pump pulsed laser with the injection time of the signal light and controls the peak power of multiple sub-pulses in the pump pulsed laser to be output according to a preset sequence. In this embodiment, the pulsed laser source generates pump light λ3 with a center wavelength of 1030 nm. The pump light is in the form of a pump pulsed laser, and the repetition frequency (f1) of the small pulses in the pulsed laser is 50 MHz. The timing controller performs two key synchronization controls: first, it controls the overall emission time of the pump pulsed laser to synchronize it with the injection time of the signal light; second, it controls the peak power of multiple sub-pulses in the pump pulsed laser to be output according to a preset sequence that increases with the number of cycles of the signal light. By controlling the power of the pump pulsed laser according to the sequence of increasing cycles, it matches the process of the signal light gradually increasing in energy during the cycle in real time, achieving optimal energy transfer efficiency while avoiding the thermal effects or nonlinear damage caused by traditional high-power single-pulse pumping.

[0062] In this embodiment, the timing controller is an electronic control system based on programmable logic or a high-speed microprocessor; in this embodiment, it is an FPGA chip.

[0063] In this embodiment, the timing controller uses the clock signal provided by the seed light source as a reference to generate precisely synchronized electronic control signals: The first path sends a main trigger signal to the pulse train laser source and controls the source to generate a pump pulse train laser containing N sub-pulses according to a preset increasing power sequence; the second path sends a quarter-wave voltage and a zero-voltage switching sequence to the Pockelscher cell (PC) electro-optic modulator. This sequence is designed to be in a zero-voltage state before seed light injection, maintain a quarter-wave voltage after seed light injection to circulate it within the cavity, and switch the polarization state to export the seed light after the Nth cycle. During the reset phase, that is, after output is completed, the voltage is restored to zero before the next seed light pulse is injected. Here, N is a positive integer.

[0064] In this embodiment, the optical retarder TD employs an optical delay structure composed of four mirrors. The optical retarder TD includes a precisely movable translation stage and two mirrors mounted on the translation stage. The other two mirrors are fixed to the optical platform, forming a variable optical path reflection loop together with the two movable mirrors. By driving the translation stage to change the axial position of the movable mirrors, the optical path length of the pump pulse train laser in the reflection loop can be continuously changed.

[0065] As shown in Figure 1, the signal light to be amplified passes through the first half-wave plate H1, which adjusts the polarization state of the signal light to the polarization state required by the isolator, ensuring maximum transmission and optimal isolation. The polarization-adjusted signal light is then sequentially incident on the optical isolator ISO, the first polarizing beam splitter M, the optical rotator R, and finally passes through the second half-wave plate H2, where it is adjusted to P-polarized light. The optical isolator ISO prevents reflected light from damaging the seed source in subsequent optical paths. The second half-wave plate H2 finely adjusts the polarization direction of the signal light, adjusting it to P-polarized light, i.e., the first polarization state.

[0066] The injected P-polarized signal light, after polarization adjustment, enters the linear standing wave optical path through the second polarization beam splitter M2, which belongs to the optical resonant cavity structure module, when no voltage is applied to the Pockel cell PC. After entering the linear standing wave optical path, the signal light passes through the Pockel cell PC, the quarter-wave plate Q, and the first high-reflection mirror M1, then reflects back along the original optical path, passing through the quarter-wave plate Q again to become S-polarized light. After passing through the Pockel cell PC, a quarter-wave voltage is applied to the Pockel cell PC, and the light is reflected by the second polarization beam splitter M2 to the beam combiner M3, the KTP crystal C, and then to the second high-reflection mirror M4. After reflection by the second high-reflection mirror M4, the light passes through the KTP crystal C, the beam combiner M3, and the second polarization beam splitter M2 again, completing one cycle. At this point, the signal light is S-polarized. Since the second polarization beam splitter M2, which is part of the optical resonant cavity structure module, transmits P-polarized light and reflects S-polarized light, the signal light cannot pass through the second polarization beam splitter M2 to continue its cyclic amplification within the optical resonant cavity structure module. When signal light needs to be output, the signal light is reflected by the first high-reflection mirror M1, then passes through the quarter-wave plate Q and the Pockel cell PC, which changes the quarter-wave voltage applied to the Pockel cell PC to zero. The signal light is then reflected again by the second polarizing beam splitter M2, then by the beam combiner M3, the KTP crystal C, and the second high-reflection mirror M4, then by the KTP crystal C, the beam combiner M3, the second polarizing beam splitter M2, the Pockel cell PC, the quarter-wave plate Q, and the first high-reflection mirror M1. After passing through the quarter-wave plate Q again, the polarization state becomes P polarization state, and after passing through the Pockel cell PC, it is output from the second polarizing beam splitter M2.

[0067] Simultaneously with the injection of the signal light, the timing controller sends a master trigger signal to the pump pulse train laser source. The 1030nm pump light, precisely adjusted by the optical delay unit TD, ensures that the first sub-pulse of the pump pulse train perfectly coincides, both temporally and spatially, with the seed light pulse arriving first at the nonlinear crystal C. Both undergo optical parametric amplification within the KTP crystal C, resulting in energy transfer of the pump photons and the signal light receiving its first energy boost.

[0068] The amplified signal light λ1, along with the residual pump light λ3 and the newly generated idler light λ2, reaches the second high-reflectivity mirror M4. The second high-reflectivity mirror M4 is designed to be highly reflective of the signal light at 1568.5 nm and highly transparent of the pump light at 1030 nm and the idler light. Therefore, the signal light is reflected back into the optical resonant cavity, while the residual pump light and idler light are transmitted out of the cavity and eliminated, effectively preventing subsequent inverse conversion.

[0069] The Pockel cell PC is under pressure. The signal light reflected by the second high-reflectivity mirror M4 returns along its original path, passing again through the nonlinear crystal C (without pumping), beam combiner M3, second polarizing beam splitter M2, and Pockel cell PC. Since the signal light still maintains its S-polarization state, it is reflected by the second polarizing beam splitter M2 and reaches the first high-reflectivity mirror M1 at the other end. The signal light is highly reflected by the first high-reflectivity mirror M1 and propagates in the opposite direction again, following the original optical path to the second polarizing beam splitter M2, entering the next cycle. Thus, the signal light completes one round trip within the cavity, undergoing effective amplification.

[0070] During the second to N-1 round trips of the signal light, the timing controller maintains a quarter-wave voltage applied to the Pockel cell PC, ensuring the S-polarization state of the signal light remains unchanged. This allows the light to continuously pass through the second polarization beam splitter M2 and stably cycle within the linear cavity formed by the first high-reflection mirror M1 and the second high-reflection mirror M4. Before each return of the light to the second polarization beam splitter M2, the Pockel cell PC in the polarization control module determines whether to change its polarization state based on the control signal, thus controlling the light to continue circulating within the cavity. After completing the preset N cycles of amplification, the Pockel cell PC is triggered to a zero-voltage state, changing the polarization state of the S-polarized light to the P-polarized light for output. When the P-polarized seed signal of the first polarization state reaches the second polarization beam splitter M2 of the optical resonant cavity structure module again, it is transmitted through the second polarization beam splitter M2, thus serving as the final high-energy signal light, which is output from the nonlinear frequency conversion regeneration amplification device.

[0071] This application provides a preferred technical solution where the geometric optical path length corresponding to one complete cycle of the signal light in the optical resonant cavity structure module is defined. For a linear standing wave cavity structure, the cavity length L is the total optical path length of the signal light traveling back and forth between the first high-reflection mirror M1 and the second high-reflection mirror M4. To ensure that each cycle of the signal light within the optical resonant cavity is precisely synchronized with a new sub-pulse in the pump pulse train laser, the cavity length L must satisfy a strict matching relationship with the repetition frequency f1 of the sub-pulse within the pump pulse train laser. Specifically, for the linear standing wave cavity structure:

[0072]

[0073] Where c represents the speed of light in a vacuum.

[0074] In one specific embodiment of this application, the repetition frequency f1 of the sub-pulses within the pump pulse train laser is 50 MHz. Based on the aforementioned matching relationship, if a linear standing wave cavity structure is used, the corresponding optimized cavity length L is designed to be approximately 3 meters. Following the same principle, the cavity lengths corresponding to other frequencies can be derived; for example, when f1 is 10 MHz, the linear cavity length is approximately 15 meters; when f1 is 100 MHz, the linear cavity length is approximately 1.5 meters. The parameters of the timing controller and the pump pulse train laser source are configured according to this physical relationship to ensure the effective implementation of the time-domain regeneration amplification process.

[0075] The technical solution provided in this application, based on a time-domain regenerative amplification structure using a linear standing wave cavity, consists of only a simple optical resonant cavity containing a second polarizing beam splitter M2, a first high-reflection mirror, and a second high-reflection mirror M4. A time-domain switch, formed by an electro-optic modulator Pockels cell PC integrated within the optical resonant cavity and the second polarizing beam splitter M2, controls the signal light to cycle back and forth within the same nonlinear crystal C a preset number of times. In each cycle, the signal light undergoes optical parametric amplification with a synchronous pump pulse whose power is programmed in an increasing sequence according to the cycle number. This simplifies the complex optical path of multi-stage spatial amplification in existing technologies to a single linear standing wave cavity, significantly reducing the number of optical components and resulting in a compact optical path layout. By precisely matching the cavity length and the pump pulse repetition frequency, and programming the pump power sequence, the signal light receives optimized energy injection in each cycle, thus avoiding the efficiency limitations of the OPA (Optical Partition Amplifier). The total gain of a multi-stage system is achieved within a single-stage structure, significantly improving the overall efficiency of nonlinear frequency conversion.

[0076] Example 2:

[0077] Example 2 shares the same four functional modules as Example 1: signal light injection unit, polarization control module, nonlinear action module, and pump light synchronization unit. The only difference is that the optical resonator structure module is changed from a linear standing wave cavity to a unidirectional ring cavity. All other device parameters, wavelengths, pulse widths, sub-pulse repetition frequency f1 = 50 MHz, FPGA timing control logic, and pump power increment sequence are completely identical to those in Example 1 and will not be repeated. The following will only provide a detailed description of the ring cavity's unique structure and optical path.

[0078] As shown in Figure 2, in this embodiment, the optical resonant cavity structure module is a ring cavity structure. The ring cavity structure includes two polarizing beam splitters, a beam combiner M3, and a reflector, forming a unidirectional propagating ring optical path. The nonlinear crystal C is disposed in the ring optical path. In this embodiment, these are the second polarizing beam splitter M2, the third polarizing beam splitter M6, the third high-reflectivity mirror M5, and the beam combiner M3. The second polarizing beam splitter M2 serves as the injection and output port of the optical resonant cavity. The second polarizing beam splitter M2 is configured to have high transmittance for P-polarized light and high reflectivity for S-polarized light. The signal light is injected from the second polarizing beam splitter M2 in a P-polarized state; the S-polarized state is cyclically amplified, and after amplification, it is output by the third polarizing beam splitter M6 in a P-polarized state. The beam combiner M3 is a 45° dichroic mirror, configured to have high reflectivity for the signal light λ1 and high transmittance for the pump light λ3. The third high-reflectivity mirror M5 guides the beam propagation toward the beam combiner M3 and is configured to highly reflect the signal light λ1 and pump light λ3, and highly transmit the idler light λ2. The third polarizing beam splitter M6 is a key reflection point for the closure of the unidirectional ring optical path. It is configured to highly transmit cyclic polarized light to maintain the optical path loop and highly reflect polarized light orthogonal to the cyclic polarization state to achieve off-loop output. It is also the cavity-end mirror in this embodiment. In this embodiment, the third polarizing beam splitter M6 is configured to highly transmit P-polarized light and highly reflect S-polarized light, thereby allowing the amplified signal light to leave the optical resonant cavity structure module during the output stage.

[0079] In this embodiment, the signal light generated by the signal light injection unit is P-polarized and injected into the Pockels cell PC, the third half-wave plate H3, the third polarizing beam splitter M6, the third high-reflection mirror M5, the KTP crystal C, and the beam combiner M3 of the optical resonant cavity structure module via the second polarizing beam splitter M2. The beam is then redirected and returns to the second polarizing beam splitter M2.

[0080] The combination of the zero-voltage Pockel cell PC and the third half-wave plate H3 modulates the polarization state of the signal light into a specific linear polarization state. This specific linear polarization state matches the high-reflection axis direction of the third polarizing beam splitter M6. The transmission and reflection axes of the second polarizing beam splitter M2 and the third polarizing beam splitter M6 are pre-rotated and aligned to the direction of this cyclic polarization state, thereby ensuring that light in this state is highly reflected by the second polarizing beam splitter M2 and the third polarizing beam splitter M6 to maintain the closure of the loop optical path. In this embodiment, the cyclic polarization state is the S-polarization state because only S-light can be highly reflected at the second polarizing beam splitter M2 and the third polarizing beam splitter M6, thus continuing to be amplified cyclically along the loop optical path. P-light will be transmitted and leak out, failing to close the loop.

[0081] In this embodiment, the Pockel cell PC acts as a control switch for the polarization state of the signal light within the cavity, and has two states: applying zero voltage and applying half-wave voltage. When the Pockel cell PC applies zero voltage, it has no effect on the polarization state of the light in the optical resonant cavity structure module. When a half-wave voltage is applied, the Pockel cell PC is equivalent to a half-wave plate, which can rotate the polarization state of the signal light by 90°. In the initial state, zero voltage is applied to the Pockel cell PC. The P-polarized signal light from the signal light injection unit is injected into the optical resonant cavity through the second polarizing beam splitter M2. After passing through the Pockel cell PC and the third half-wave plate H3, the signal light changes from P-polarized to S-polarized. At this time, a half-wave voltage is applied to the Pockel cell PC. The signal light is reflected in the annular cavity at the third polarizing beam splitter M6. After passing through the third high-reflection mirror M5, KTP crystal C, and beam combiner M3, it is reflected at the second polarizing beam splitter M2. It passes through the Pockel cell PC. Since the Pockel cell PC is in the state of being subjected to a half-wave voltage, the polarization state of the signal light changes from S-polarized to P-polarized. After passing through the third half-wave plate H3, the polarization state changes from P-polarized back to S-polarized. Finally, it reaches the third polarizing beam splitter M6 to complete one amplification cycle. When signal light needs to be output, zero voltage is applied to the Pockel cell PC. The polarization state of the signal light does not change after passing through the Pockel cell PC. The polarization state changes from S polarization state to P polarization state after passing through the third half-wave plate H3. The regeneration amplification ends and the signal light is output after passing through the third polarization beam splitter M6.

[0082] This application provides a preferred technical solution, which defines the geometric optical path length corresponding to the signal light completing one full cycle in an optical resonant cavity structure module. For a ring cavity structure, the cavity length L is defined as the total geometric optical path length of the signal light propagating one full cycle along a unidirectional ring optical path.

[0083] To ensure that each cycle of the signal light within the optical resonant cavity is precisely synchronized with a new sub-pulse in the pump pulse train, the cavity length L must also satisfy a strict matching relationship with the repetition frequency f1 of the sub-pulses within the pump pulse train. Unlike linear standing-wave cavities, in a ring cavity, the signal light encounters a new pump sub-pulse after each complete cycle. Therefore, the cycle period, i.e., the time it takes for the light to complete one cycle, must be equal to the interval between pump sub-pulses, which must satisfy... Therefore, for a ring cavity structure, the matching relationship between its cavity length L and the sub-pulse repetition frequency f1 is expressed as follows:

[0084]

[0085] Based on the above principle and continuing the parameters of the linear cavity embodiment, in a specific embodiment of this application, the repetition frequency f1 of the sub-pulse inside the pump pulse train laser is also 50 MHz, and the corresponding optimized cavity length L is designed to be about 6 meters.

[0086] In this embodiment, the optical resonant cavity structure module is a ring cavity structure, and the signal light is constrained to propagate in only one direction, with no back-propagating light interfering with it. Therefore, the light wave propagating inside the cavity is a light wave with a peak intensity moving uniformly in space. For any fixed point inside the nonlinear crystal C, it is not continuously under high intensity, but is periodically swept by the peak of the traveling wave pulse, avoiding the spatial hole burning effect.

[0087] This application provides a nonlinear frequency conversion regenerative amplification device, in which an optical resonant cavity structure is used to achieve time-domain regenerative amplification. The linear standing-wave cavity structure has advantages such as simple optical path, intuitive assembly and adjustment, and high stability; the ring cavity structure avoids spatial hole burning effects, which is beneficial for obtaining better beam quality and thermal management. Both utilize a time-domain switch composed of an electro-optic modulator and polarization control elements to control the signal light to circulate within the cavity a preset number of times, and sequentially interact with a synchronously and power-programmed pump pulse train in a single nonlinear crystal C. This achieves highly efficient nonlinear frequency conversion and amplification, traditionally requiring multi-stage complex systems, in a single-stage compact structure, significantly improving the system's integration, efficiency, and controllability.

[0088] Example 3:

[0089] Example 3 describes a method for nonlinear frequency conversion regenerative amplification using a nonlinear frequency conversion regenerative amplification device as described in Examples 1 and 2. It features the same four functional modules: signal light injection unit, polarization control module, nonlinear action module, and pump light synchronization unit. Device parameters, wavelength, pulse width, sub-pulse repetition frequency f1 = 50 MHz, FPGA timing control logic, and pump power increment sequence are completely identical to those in Examples 1 and 2 and will not be repeated.

[0090] This application also provides a nonlinear frequency conversion regenerative amplification method, including:

[0091] S1. Inject linearly polarized signal light into the optical resonant cavity in the first polarization state.

[0092] Prepare a linearly polarized signal light to be amplified, and adjust the polarization state of the signal light to the first polarization state. Inject the signal light with the first polarization state into the optical resonant cavity.

[0093] S2. The polarization state of the signal light is changed by an electro-optic modulator, so that the signal light cycles back and forth in the optical resonant cavity a preset number of times.

[0094] An electro-optic modulator, positioned within the optical resonant cavity, controls the signal light to circulate within the cavity N times, where N is a positive integer greater than 1. During the first N-1 cycles of the N cycles, the electro-optic modulator is controlled to maintain the signal light in a polarization state that allows it to continue circulating within the cavity.

[0095] S3. During each round trip of the signal light, it undergoes optical parametric amplification with the pump pulse train laser in the nonlinear crystal C.

[0096] A pump pulse train laser beam is generated, containing N sub-pulses in the time domain. The pump pulse train laser is controlled to synchronize with the signal light circulating within the optical resonant cavity. Specifically, the k-th sub-pulse (k=1, 2, …, N) in the pump pulse train is made to coincide, both temporally and spatially, with the signal light pulse undergoing the k-th cycle at the nonlinear crystal C. The peak power of the N sub-pulses in the pump pulse train laser is controlled to be output according to a preset sequence. At each coincidence, the signal light and the corresponding pump sub-pulse undergo optical parametric amplification in the nonlinear crystal C, thus successively amplifying the energy of the signal light.

[0097] S4. After completing the preset number of cycles, the signal light is output from the optical resonator in a second polarization state orthogonal to the first polarization state.

[0098] After the signal light completes the Nth cycle of amplification, the electro-optic modulator is controlled to change its polarization state, switching it from the first polarization state to a second polarization state orthogonal to the first polarization state. The amplified signal light in the second polarization state is then output from the optical resonator.

[0099] This application provides a method for nonlinear frequency conversion regenerative amplification. Through a time-domain regenerative amplification approach, the nonlinear frequency conversion process is deeply integrated with a controllable optical resonant cavity. An electro-optic modulator is used to precisely program and control the number of cycles and output timing of the signal light within the cavity, ensuring that it undergoes multiple sequential optical parametric amplifications with a synchronous, power-increasing pump pulse train within a single nonlinear crystal. This solves the inherent problems of low efficiency in single-stage nonlinear conversion and the complexity and bulkiness of multi-stage spatial amplification systems in existing technologies. A single device with a simple structure and controllable timing achieves high-gain, high-stability, and high-integration nonlinear laser frequency conversion and amplification.

[0100] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0101] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A nonlinear frequency conversion regenerative amplification device, characterized in that, include: The system includes a signal light injection unit, a regenerative amplification cavity unit, and a pump light synchronization unit; the signal light injection unit is used to inject linearly polarized signal light into the regenerative amplification cavity unit. The regenerative amplification cavity unit includes an optical resonant cavity structure module, a polarization control module, and a nonlinear action module. The optical resonant cavity structure module includes at least one polarizing beam splitter, one beam combiner, and at least one reflecting mirror. The polarizing beam splitter, the beam combiner, and the reflecting mirror together constitute an optical resonant cavity for the round-trip propagation of the signal light. The polarization control module includes an electro-optic modulator disposed within the optical resonant cavity. The electro-optic modulator is used to change the polarization state of the signal light, causing the signal light to cycle back and forth within the optical resonant cavity a preset number of times before being output through the polarizing beam splitter. The nonlinear action module includes a nonlinear crystal disposed within the optical resonant cavity structure module. The pump light synchronization unit is used to generate a pump pulse train laser. The pump pulse train laser is synchronized with the cyclic process of the signal light, causing the cyclic signal light and the pump pulse train laser to undergo multiple optical parametric amplifications in the nonlinear crystal.

2. The apparatus according to claim 1, characterized in that, The optical resonant cavity structure module is a linear standing wave cavity structure; the linear standing wave cavity structure includes the polarizing beam splitter, the beam combiner, and two high-reflection mirrors, forming a linear standing wave optical path; the nonlinear crystal is disposed in the linear standing wave optical path.

3. The apparatus according to claim 1, characterized in that, The optical resonant cavity structure module is a ring cavity structure; the ring cavity structure includes two polarizing beam splitters, one beam combiner and one reflector, forming a unidirectional propagating ring optical path; the nonlinear crystal is disposed in the ring optical path.

4. The apparatus according to claim 1, characterized in that, The polarizing beam splitter is configured to allow the signal light to enter the optical resonant cavity in a first polarization state, and after the signal light completes a preset number of cycles, to output the signal light from the optical resonant cavity in a second polarization state; the second polarization state is orthogonal to the first polarization state.

5. The apparatus according to claim 1, characterized in that, The signal light injection unit includes a seed light source, an optical isolator, and a polarization adjustment element arranged sequentially.

6. The apparatus according to claim 1, characterized in that, The electro-optic modulator is a Pockel cell.

7. The apparatus according to claim 1, characterized in that, The pump light synchronization unit includes a pulse train laser source, a timing controller, and an optical delay unit. The timing controller is used to synchronize the emission time of the pump pulse train laser with the injection time of the signal light, and to control the peak power of multiple sub-pulses in the pump pulse train laser to be output according to a preset sequence. The optical delay unit is used to adjust the optical path of the pump pulse train laser, so that each sub-pulse in the pump pulse train laser and the signal light pulse corresponding to the number of cycles in the optical resonant cavity achieve time synchronization and spatial overlap of the light spots when they reach the nonlinear crystal.

8. The apparatus according to claim 7, characterized in that, The timing controller is configured to control the peak power of multiple sub-pulses in the pump pulse train laser and output them according to a preset sequence that increases with the number of cycles of the signal light in the optical resonant cavity.

9. The apparatus according to claim 1, characterized in that, The optical resonant cavity structure module includes a cavity end mirror; the cavity end mirror has high reflectivity to signal light and high transmittance to pump light and idler light generated by optical parametric amplification.

10. A nonlinear frequency conversion regenerative amplification method based on the apparatus of any one of claims 1 to 9, characterized in that, include: The linearly polarized signal light is injected into the optical resonant cavity in the first polarization state; The polarization state of the signal light is changed by an electro-optic modulator, causing the signal light to cycle back and forth in the optical resonant cavity a preset number of times. During each round trip of the signal light, the signal light and the pump pulse train laser undergo optical parametric amplification in the nonlinear crystal; After completing a preset number of cycles, the signal light is output from the optical resonator in a second polarization state orthogonal to the first polarization state.

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