A method of controlling ASE of a laser amplifier

Abstract

The application provides a method for controlling ASE of a laser amplifier, comprising the following process: configuring a controllable resonant cavity shared by a gain medium of the laser amplifier for the gain medium; through loss modulation on the controllable resonant cavity, the gain medium stores energy and amplifies signal light during a signal light incidence period, and the remaining energy is rapidly discharged at the end of the signal light, so that the gain is lower than the ASE generation threshold, thereby suppressing ASE generation from the source. The application actively regulates the energy state of the gain medium, discharges the excess stored energy before ASE generation, so that the gain is always lower than the ASE generation threshold, and ASE is eliminated from the generation mechanism. Compared with the traditional passive attenuation method after ASE generation, there is no signal light loss, the suppression is more thorough, the response is fast, and the application is suitable for various pulse laser amplifier systems. Moreover, the controllable resonant cavity and the laser amplifier share the same gain medium, and no additional gain module needs to be added, so that the optical path is simple and the integration degree is high, and the system complexity and hardware cost are significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of laser amplification technology, specifically relating to a method for controlling a laser amplifier ASE. Background Technology

[0002] In pulsed laser amplifiers, the gain medium is continuously pumped and accumulates population inversion during periods without signal light. When the number of inverted particles reaches a certain level, spontaneous emission photons are continuously amplified, forming strong amplified spontaneous emission (ASE). In practical systems, ASE has the following effects: (1) energy loss and reduced signal-to-noise ratio. For high-gain, ultra-short pulse (such as chirped pulse amplification, CPA) systems, ASE will become pre-pulse noise, affecting the signal-to-noise ratio and even damaging optical devices; (2) performance saturation. In fiber amplifiers, strong ASE will deplete the number of particles in the upper energy level, resulting in "saturation" of the output power; (3) measurement interference. The value measured by the power meter often contains ASE components, requiring the use of a spectrometer or chopper method to distinguish between signal and noise.

[0003] Traditional ASE suppression methods often employ passive approaches such as time-domain filtering (using a pulse picker to filter signals over time and remove ASE background), spatial / spectral filtering (using pinhole apertures or bandpass filters to filter off-axis and out-of-band noise), and interstage isolation (inserting Faraday isolators, filters, or saturable absorbers between amplification stages). These methods can only attenuate ASE after it occurs, and cannot eliminate it at its source. Furthermore, they introduce signal light loss and reduce system efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling a laser amplifier ASE, which can at least solve some of the defects existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for controlling a laser amplifier ASE includes the following steps: Configure a controllable resonant cavity that shares the gain medium with the laser amplifier; By performing loss modulation on the controllable resonant cavity, the gain medium stores energy and amplifies the signal light during the signal light incident period, and rapidly releases the remaining energy at the end of the signal light period, so that the gain is lower than the ASE generation threshold, thereby suppressing ASE generation from the source.

[0006] Furthermore, the loss modulation of the controllable resonant cavity is achieved through Q modulation, enabling the controllable resonant cavity to switch between a high-loss state and a low-loss oscillation state.

[0007] Furthermore, the specific process of Q modulation is as follows: Before the signal light is incident, the Q-modulator is turned off, so that the controllable resonant cavity is in a high-loss state and the gain medium accumulates a population inversion. During the passage of the signal light through the gain medium, the Q-modulator remains off, and the high gain of the gain medium amplifies the signal light. During the gap period after the signal light passes through, the controllable Q modulation device is turned on, the controllable resonant cavity starts to oscillate and outputs oscillating light, which quickly consumes the remaining energy stored in the gain medium, so that the gain is lower than the ASE generation threshold.

[0008] Furthermore, before the signal light is incident, the turn-off time of the control Q-modulator is advanced by a time length Δt before the signal light is incident, and is adaptively determined according to the operating parameters of the laser amplifier; the operating parameters include at least one of the gain medium type, pump power, and target amplification factor.

[0009] Furthermore, the controllable resonant cavity includes a gain medium, a Q-modulation device, a resonant cavity output mirror, and at least one resonant cavity reflector, wherein the controllable resonant cavity is one of a linear cavity, a folded cavity, or a ring cavity.

[0010] Furthermore, the Q-modulation device is any one of an electro-optic Q-switch, an acousto-optic Q-switch, or a magneto-optic Q-switch.

[0011] Furthermore, the Q modulation is performed synchronously with the signal light pulse, and the Q modulation timing corresponds one-to-one with the signal light pulse timing.

[0012] Furthermore, the signal light and the oscillation light of the controllable resonant cavity share the gain region of the gain medium, and their optical axes are coaxial or approximately parallel.

[0013] Furthermore, the gain medium is a laser crystal.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for controlling ASE in a laser amplifier provided by this invention actively regulates the energy state of the gain medium to release excess stored energy before ASE is generated, ensuring that the gain is always below the ASE generation threshold, thus eradicating ASE from its generation mechanism. Compared with the traditional passive attenuation method after ASE is generated, this method has no signal light loss, more thorough suppression, and faster response, and is suitable for various pulsed laser amplifier systems. Moreover, the controllable resonant cavity and the laser amplifier share the same gain medium, eliminating the need for additional gain modules, resulting in a simple optical path, high integration, and significantly reduced system complexity and hardware cost.

[0015] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0016] Figure 1This is a schematic diagram illustrating the principle of controlling the laser amplifier ASE according to the present invention; Figure 2 This is a timing diagram of Q modulation in an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached diagram: 1. Signal light; 2. Resonant cavity mirror; 3. Q-modulator; 4. Gain medium; 5. Resonant cavity output mirror; 6. Oscillating light. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection", and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, an abutting connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] like Figure 1 As shown, for a laser amplifier, signal light 1 is amplified by gain medium 4. However, for a pulsed laser, signal light 1 is pulsed and not always present. When there is no pulse, gain medium 4 continuously accumulates energy, which generates ASE (associated energy transfer). To suppress ASE, this embodiment provides a method for controlling ASE in a laser amplifier, specifically including the following steps: S1. Configure a controllable resonant cavity that shares the gain medium 4 with the laser amplifier.

[0023] S2. By performing loss modulation on the controllable resonant cavity, the gain medium 4 stores energy and amplifies the signal light 1 during the incident period of the signal light 1, and rapidly releases the remaining energy at the end of the signal light 1 period, so that the gain is lower than the ASE generation threshold, thereby suppressing the generation of ASE from the source.

[0024] In some embodiments, the loss modulation of the controllable resonant cavity can be achieved by Q modulation, which allows the controllable resonant cavity to switch between a high-loss state and a low-loss oscillation state. In the high-loss state, the gain medium 4 accumulates a population inversion and amplifies the signal light 1. In the low-loss oscillation state, the controllable resonant cavity emits light and consumes the energy stored in the gain medium 4.

[0025] Specifically, the Q modulation process is as follows: Before the signal light 1 is incident, the Q modulation device 3 is turned off, so that the controllable resonant cavity does not emit light and is in a high-loss state, and the gain medium 4 accumulates population inversion; during the period when the signal light 1 passes through the gain medium 4, the Q modulation device 3 is kept off, and the high gain of the gain medium 4 is used to amplify the signal light 1; during the gap period after the signal light 1 passes, the Q modulation device 3 is turned on, the controllable resonant cavity starts to oscillate and outputs oscillating light 6, which quickly consumes the remaining energy stored in the gain medium 4, so that the gain is lower than the ASE generation threshold.

[0026] Furthermore, before signal light 1 is incident, the turn-off time of the control Q modulator 3 is advanced by a time length Δt before the incident time of signal light 1, such as... Figure 2 As shown, Δt = t 02 -t 01 =t 12 -t 11 =t 22 -t 11 =t 32 -t 31 The specific value of this time length Δt is related to the operating parameters of the laser amplifier (such as the type of gain medium, pump power, target amplification factor, etc.). For example, different gain media 4 have different upper level lifetimes and stimulated emission cross sections, resulting in different population inversion build-up speeds. The higher the pump power, the faster the energy storage speed, and the shorter the required advance time. The larger the target amplification factor, the more inverted particles need to be accumulated, and the longer the required advance time. By adaptively setting the advance turn-off time Δt according to the above operating parameters, it can be ensured that the gain medium 4 reaches the required gain when the signal light 1 is incident, which ensures the amplification effect and avoids ASE caused by excessive energy storage time.

[0027] Preferred, such as Figure 2As shown, the Q modulation is executed synchronously with the signal light 1 pulse. The Q modulation timing corresponds one-to-one with the signal light 1 pulse timing. The turn-off, hold, and turn-on actions of the Q modulation device 3 are precisely matched with the pre-incident, during-incident, and post-incident periods of the signal light 1, respectively. Each signal light 1 pulse corresponds to a complete set of Q modulation device 3 actions. Through synchronous control, it is ensured that the gain medium 4 completes energy storage before the arrival of the signal light 1, does not generate resonance interference during the amplification of the signal light 1, and instantly releases the remaining energy after the signal light 1 ends, so that the gain quickly falls back to below the ASE generation threshold, thus completely eliminating the conditions for ASE generation from the time dimension.

[0028] The optimized design reuses the gain region of the gain medium for the signal light 1 and the oscillation light of the controllable resonant cavity, and the optical axes of the two are arranged in a coaxial or approximately parallel manner with a very small angle. This eliminates the need to add an additional gain medium 4 and does not change the main structure of the original laser amplifier. It can make full use of the energy storage and dissipation regions of the gain medium 4, ensuring the signal light amplification efficiency and ASE suppression effect.

[0029] In this embodiment, the controllable resonant cavity can be any one of a linear cavity, a folded cavity, or a ring cavity, all of which can achieve active control of the energy of the gain medium 4 and suppression of the ASE source. Among them, the linear cavity has a simple structure and is easy to debug; the folded cavity has a compact structure, saves space, and has good vibration resistance; the ring cavity can suppress the standing wave effect and avoid spatial hole burning, and is suitable for high power and high beam quality requirements. The cavity form of the controllable resonant cavity can be selected according to different application scenarios.

[0030] Specifically, when the controllable resonant cavity is a linear cavity, it consists of a resonant cavity mirror 2, a gain medium 4, a Q-modulator 3, and a resonant cavity output mirror 5 arranged sequentially along the same optical axis. The resonant cavity mirror 2 and the resonant cavity output mirror 5 are positioned opposite each other, forming an optical feedback loop. The gain medium 4 and the Q-modulator 3 are located within the optical feedback loop. When the controllable resonant cavity is a folded cavity, it still consists of a resonant cavity mirror 2, a gain medium 4, a Q-modulator 3, and a resonant cavity output mirror 5. However, multiple resonant cavity mirrors 2 are arranged, causing the optical axis of the controllable resonant cavity to transmit in a zigzag shape, forming a folded optical feedback loop. The gain medium 4 and the Q-modulator 3 are located within the folded optical feedback loop. When the controllable resonant cavity is a ring cavity, it still consists of a resonant cavity mirror 2, a gain medium 4, a Q-modulator 3, and a resonant cavity output mirror 5. However, multiple resonant cavity mirrors 2 are arranged, forming a closed ring optical feedback loop together with the resonant cavity output mirror 5. The gain medium 4 and the Q-modulator 3 are located within the closed ring optical feedback loop.

[0031] Optionally, the Q-modulation device 3 can be any one of an electro-optic Q-switch, an acousto-optic Q-switch, or a magneto-optic Q-switch, which has a fast response characteristic and can instantly switch the controllable resonant cavity loss state after the signal light 1 ends, realize instantaneous energy dissipation, and ensure that energy release is completed before ASE is generated, thus suppressing it completely.

[0032] Optionally, the gain medium 4 may be, but is not limited to, a laser crystal, such as Nd:YAG, Nd: Yb:YAG, etc.

[0033] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for controlling a laser amplifier ASE, characterized in that, The process includes the following: Configure a controllable resonant cavity that shares the gain medium with the laser amplifier; By performing loss modulation on the controllable resonant cavity, the gain medium stores energy and amplifies the signal light during the signal light incident period, and rapidly releases the remaining energy at the end of the signal light period, so that the gain is lower than the ASE generation threshold, thereby suppressing ASE generation from the source; the signal light and the oscillation light of the controllable resonant cavity reuse the gain region of the gain medium, and their optical axes are coaxial or parallel. The loss modulation of the controllable resonant cavity is achieved through Q modulation, which switches the controllable resonant cavity between a high-loss state and a low-loss oscillation state. The specific process of Q modulation is as follows: Before the signal light is incident, the Q-modulator is turned off, so that the controllable resonant cavity is in a high-loss state and the gain medium accumulates a population inversion. During the passage of the signal light through the gain medium, the Q-modulator remains off, and the high gain of the gain medium amplifies the signal light. During the gap after the signal light passes through, the Q modulation device is turned on, the controllable resonant cavity starts to oscillate and outputs oscillating light, which quickly consumes the remaining energy stored in the gain medium, making the gain lower than the ASE generation threshold. The Q modulation is executed synchronously with the signal light pulse, and the Q modulation timing corresponds one-to-one with the signal light pulse timing.

2. The method for controlling the laser amplifier ASE as described in claim 1, characterized in that, Before the signal light is incident, the turn-off time of the control Q-modulator is advanced by a time length Δt before the signal light is incident, and is adaptively determined according to the operating parameters of the laser amplifier; the operating parameters include at least one of the gain medium type, pump power, and target amplification factor.

3. The method for controlling the laser amplifier ASE as described in claim 1, characterized in that, The controllable resonant cavity includes a gain medium, a Q-modulation device, a resonant cavity output mirror, and at least one resonant cavity reflector. The controllable resonant cavity is one of a linear cavity, a folded cavity, or a ring cavity.

4. The method for controlling the laser amplifier ASE as described in claim 1, characterized in that, The Q-modulation device is any one of an electro-optic Q-switch, an acousto-optic Q-switch, or a magneto-optic Q-switch.

5. The method for controlling the laser amplifier ASE as described in claim 1, characterized in that, The gain medium is a laser crystal.

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