A device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification

Abstract

The present invention discloses a device for measuring the temporal gain evolution and relaxation process of CO2 laser amplification, belonging to the field of laser technology. The device comprises: a continuous CO2 laser seed source, a short-pulse CO2 laser seed source, a first beam splitter located in the outgoing optical path of the short-pulse CO2 laser seed source; a pulsed CO2 laser information detection module located in the transmitted optical path of the first beam splitter; a first thin-film polarizer located at the intersection of the reflected optical path of the first beam splitter and the outgoing optical path of the continuous CO2 laser seed source; a CO2 laser amplifier, a second thin-film polarizer, a second beam splitter, a chopper wheel module, and a first mercury cadmium telluride detector located sequentially in the outgoing optical path of the first thin-film polarizer; and a time gating circuit for controlling the on / off timing of the continuous CO2 laser seed source, the short-pulse CO2 laser seed source, and the CO2 laser amplifier. This device simplifies traditional gain measurement devices while simultaneously studying various relaxation phenomena during the amplification process.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and more particularly, relates to a device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification. Background Art

[0002] High-power, high-repetition-rate, high-beam-quality short-pulse CO2 lasers, acting as the driving light source in conjunction with a liquid tin target, are currently the mainstream approach for generating 13.5nm extreme ultraviolet light. This is because CO2 lasers offer the optimal combination of achievable average power, extreme ultraviolet light conversion efficiency, and minimal fragmentation from bombarding the target. CO2-driven lasers must meet requirements for a duration of 5-20ns, a repetition rate exceeding tens of kilohertz, and an average power of tens of kilowatts, necessitating the use of a master oscillator power amplification structure. Therefore, research on the temporal gain evolution of nanosecond short-pulse CO2 laser amplification is a crucial topic.

[0003] The amplification efficiency of nanosecond pulses in CO2 laser amplifiers is lower than that of long pulses and continuous lasers. The input laser pulse oscillating on a single rotation line is limited by the extreme rotation relaxation time constant and does not have enough time to couple out all the energy stored in the CO2 laser amplifier. Another factor that limits the effective amplification of nanosecond pulses is the 00 0 1 and 10 0 Intramodal relaxation between the zero vibrational energy levels, as well as Fermi resonance relaxation between the symmetric vibrational mode v1 and the bending mode v2, reduces amplifier energy extraction when the intramodal relaxation time is greater than or equal to the pulse duration. Three methods exist to improve the amplification performance of nanosecond short-pulse CO2 lasers. First, increasing the laser gas pressure, as relaxation time is inversely proportional to pressure. Second, extracting energy from the amplifier through multi-line or stimulated emission from two frequency bands of the CO2 laser. The results achieved with these techniques depend on the ratio of pulse duration to rotational relaxation time, the intensity of the incident pulse, and the uniformity of the beam profile. Third, using multipass amplifiers to achieve higher amplified output by increasing the optical path length requires optimal gain recovery before pulse re-amplification, which is closely related to the various relaxation times. Therefore, studying the impact of various relaxation phenomena on amplification performance during short-pulse CO2 laser amplification is also an important topic.

[0004] Therefore, in the main oscillator power amplifier structure, when using nanosecond short-pulse CO2 laser as the seed source for amplification, it is necessary to pay attention not only to the time-domain gain evolution of the amplifier, but also to the various relaxation times during the amplification process, such as the resonant energy transfer between the gas mixture N2 and the upper energy level of the CO2 laser, intra-mode relaxation, Fermi resonance relaxation, rotational relaxation, etc. The traditional way of measuring amplifier gain uses two independent and usually different CO2 laser detectors to measure the laser power and pulse waveform before and after amplification. An oscilloscope with a differential input is required to subtract the detection beam from the amplified laser (i.e., the gain plus the detection laser signal). The relaxation process in the CO2 laser gas mixture has been given by different domestic and foreign workers. For example, foreign scholar EE Stark can measure the time history of the small signal gain near the end of the amplifier by using a continuously tunable laser probe perpendicular to the pulse direction. 0 1 and 10 0 However, these solutions are difficult to implement and cannot be combined with the time-domain evolution of the amplifier gain to optimize the amplification performance.

[0005] In summary, the existing technology lacks a solution that can effectively monitor the unamplified and amplified probe beams in a single measurement, obtain the time evolution of the laser amplifier gain within a fixed spatial region, determine the maximum gain time of the amplifier to inject the seed laser, and analyze the relaxation phenomenon during the amplification process. Such analysis can in turn be used to optimize laser amplification performance. Summary of the Invention

[0006] In response to the defects of the existing technology and the need for improvement, the present invention provides a device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification, which aims to simplify the traditional gain measurement device while studying various relaxation phenomena in the amplification process.

[0007] To achieve the above-mentioned object, the present invention provides a device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification, comprising: a continuous CO2 laser seed source, a short-pulse CO2 laser seed source, and a first spectroscope located in the outgoing light path of the short-pulse CO2 laser seed source; a pulse CO2 laser information detection module located in the transmitted light path of the first spectroscope; a first thin-film polarizer located at the intersection of the reflected light path of the first spectroscope and the outgoing light path of the continuous CO2 laser seed source; the P-polarized light of the detection signal light generated by the continuous CO2 laser seed source is completely transmitted through the first thin-film polarizer. The S-polarized light of the interference pulse signal light generated by the short-pulse CO2 laser seed source and reflected by the first beam splitter is completely reflected by the first thin-film polarizer and then beam-combined and emitted; the CO2 laser amplifier, the second thin-film polarizer, the second beam splitter, the chopper wheel module and the first mercury cadmium telluride detector are sequentially located in the output light path of the first thin-film polarizer; the absorber is located in the reflection light path of the second thin-film polarizer and the reflection light path of the second beam splitter; the time selection circuit is used to control the on and off time of the continuous CO2 laser seed source, the short-pulse CO2 laser seed source and the CO2 laser amplifier.

[0008] Furthermore, the detection signal light generated by the continuous CO2 laser seed source uses P-polarized light, and the interference pulse signal light generated by the short-pulse CO2 laser seed source uses S-polarized light.

[0009] Furthermore, the short pulse CO2 laser seed source adopts a multi-spectral line short pulse CO2 laser seed source, which is used to generate interference pulse signal lights with different spectral lines and different pulse widths.

[0010] Furthermore, the chopper wheel module includes: two lenses and a rotating chopper wheel located between the two lenses, and the rotation speed of the rotating chopper wheel is adjustable.

[0011] Furthermore, the pulse CO2 laser information detection module includes a second mercury cadmium telluride detector and a wavelength meter, which are used to detect the time domain waveform and wavelength of the output spectrum line of the short pulse CO2 laser seed source.

[0012] Furthermore, the CO2 laser amplifier is a radio frequency excited axial fast flow CO2 laser amplifier.

[0013] Furthermore, the measurement process of the device includes: a time gating circuit turns on a continuous CO2 laser seed source and a CO2 laser amplifier, turns off a short-pulse CO2 laser seed source, and after a set time, uses a first mercury cadmium telluride detector to obtain an amplifier gain pulse signal and determine the amplifier gain and the maximum gain moment; the time gating circuit turns on the short-pulse CO2 laser seed source at the maximum gain moment, uses a pulsed CO2 laser information detection module to measure the wavelength and pulse width of the interference pulse signal light, the amplified interference pulse signal is reflected by a second thin-film polarizer into the absorber, and uses the first mercury cadmium telluride detector to obtain the gain pulse signal of the amplifier after interference, so as to measure the corresponding relaxation process.

[0014] Furthermore, when measuring the corresponding relaxation process, the pulse width of the interfering pulse signal light is gradually shortened and the pulse spectrum line is changed.

[0015] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0016] (1) A device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification is provided, which is provided with a continuous CO2 laser seed source and a short-pulse CO2 laser seed source, and the opening and closing of the two seed sources are controlled by a time gating circuit. The polarization direction of the detection signal light is perpendicular to the polarization direction of the interference pulse signal. After being combined by a first thin-film polarizer, the two are coaxially passed through the CO2 laser amplifier and then split by a second thin-film polarizer. Thus, the amplified detection beam after the pulse interference signal can be obtained to determine the time-domain gain evolution of nanosecond short-pulse amplification, and the relaxation process occurring on the nanosecond time scale can be tracked, so that the device can measure both the time-domain gain evolution phenomenon of CO2 laser amplification and the relaxation process of CO2 laser amplification, and the device structure is simple;

[0017] (2) The measurement of the time-domain gain evolution and relaxation process of CO2 laser amplification can be achieved by using only the first HgCdTe detector, avoiding the use of two different detectors to detect the laser before and after amplification respectively. The unamplified and amplified detection beams can be effectively monitored in a single measurement, and the time evolution of the laser amplifier gain in a fixed spatial region can be obtained. The maximum gain time of the amplifier can be determined to inject the seed laser.

[0018] (3) The short pulse CO2 laser seed source uses a multi-spectral short pulse CO2 laser seed source, which can achieve different spectral lines and different pulse width outputs, study the amplification process and relaxation process under various conditions, and optimize the amplification performance;

[0019] (4) The laser seed source is synchronized with the rotating chopper wheel. By controlling the rotation speed of the chopper wheel, not only can pulses of appropriate width be generated at the detector, but the heating effect of the laser on the detector can also be weakened, and high-intensity short pulses can be accurately controlled to be injected into the amplifier at the moment of maximum gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of a device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification provided by an embodiment of the present invention;

[0021] Figure 2 This is a flowchart of the working process of the device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification provided by an embodiment of the present invention.

[0022] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0023] 1 is a continuous CO2 laser seed source, 2 is a short pulse CO2 laser seed source, 3 is a first spectroscope, 4 is a pulse CO2 laser information detection module, 41 is a second mercury cadmium telluride detector, 42 is a wavelength meter, 5 is a first thin film polarizer, 6 is a CO2 laser amplifier, 7 is a second thin film polarizer, 8 is a second spectroscope, 9 is a chopper wheel module, 10 is a first mercury cadmium telluride detector, 11 is an absorber, and 12 is a time gating circuit. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0025] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0026] Figure 1 Schematic diagram of the structure of the device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification provided by an embodiment of the present invention. Figure 1 , combined with Figure 2 , the device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification in this embodiment is described in detail.

[0027] The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification includes: a continuous CO2 laser seed source 1, a short-pulse CO2 laser seed source 2, a first spectroscope 3, a pulsed CO2 laser information detection module 4, a first thin-film polarizer 5, a CO2 laser amplifier 6, a second thin-film polarizer 7, a second spectroscope 8, a chopper wheel module 9, a first mercury cadmium telluride detector 10, an absorber 11 and a time gating circuit 12.

[0028] The first beam splitter 3 is located in the outgoing light path of the short pulse CO2 laser seed source 2. The pulse CO2 laser information detection module 4 is located in the transmitted light path of the first beam splitter 3. The first thin film polarizer 5 is located at the intersection of the reflected light path of the first beam splitter 3 and the outgoing light path of the continuous CO2 laser seed source 1.

[0029] The P-polarized light of the detection signal light generated by the continuous CO2 laser seed source 1 is completely transmitted by the first thin-film polarizer 5, and the S-polarized light of the interference pulse signal light generated by the short-pulse CO2 laser seed source 2 reflected by the first beam splitter 3 is completely reflected by the first thin-film polarizer 5, and then combined and emitted.

[0030] A CO2 laser amplifier 6, a second thin-film polarizer 7, a second beam splitter 8, a chopper wheel module 9, and a first mercury cadmium telluride detector 10 are sequentially positioned in the output optical path of the first thin-film polarizer 5. An absorber 11 is positioned in the reflected optical path of the second thin-film polarizer 7 and the reflected optical path of the second beam splitter 8. A time gating circuit 12 is used to control the on / off timing of the continuous CO2 laser seed source 1, the short-pulse CO2 laser seed source 2, and the CO2 laser amplifier 6.

[0031] The continuous CO2 laser seed source 1 is used to provide detection signal light. Preferably, the detection signal light generated by the continuous CO2 laser seed source 1 is P-polarized light.

[0032] The short-pulse CO2 laser seed source 2 is used to provide interfering pulse signal light. Preferably, the interfering pulse signal light generated by the short-pulse CO2 laser seed source 2 is S-polarized light. Further preferably, the short-pulse CO2 laser seed source 2 is a multi-spectral short-pulse CO2 laser seed source, which is used to generate interfering pulse signal light with different spectral lines and different pulse widths.

[0033] The first beam splitter 3 splits the intensity of the interference pulse signal light generated by the short pulse CO2 laser seed source 2 according to a certain reflection and transmission ratio. The transmitted part enters the pulse CO2 laser information detection module 4, and the reflected part enters the first thin film polarizer 5 at the Brewster angle.

[0034] The pulse CO2 laser information detection module 4 includes a second mercury cadmium telluride detector 41 and a wavelength meter 42, which are used to detect the time domain waveform and wavelength of the output spectrum line of the short pulse CO2 laser seed source 2.

[0035] The first thin-film polarizer 5 is composed of a coated flat plate, which forms a Brewster angle with the incident beam. The thin-film coating enhances the reflectivity of S-polarized light while maintaining high transmittance for the P-polarized component, allowing the detection signal light to combine with the interference pulse signal and enter the CO2 laser amplifier 6 on the same axis.

[0036] The CO2 laser amplifier 6 is used to amplify the power of the seed source. Preferably, the CO2 laser amplifier 6 is a radio frequency excited axial fast flow CO2 laser amplifier. The structure of the radio frequency excited axial fast flow CO2 laser amplifier is relatively complex. Figure 1 The figure only represents the main cavity of the amplifier, and other auxiliary systems are not reflected, such as: laser RF power supply and matching network, control system, water cooling system, mixing unit, etc.

[0037] The second thin-film polarizer 7 is used to completely transmit P-polarized light and completely reflect S-polarized light, thereby separating the amplified detection signal light from the interference pulse signal light. The second beam splitter 8 is placed before the chopper wheel module 9 to weaken the intensity of the amplified continuous laser.

[0038] The chopper wheel module 9 includes two lenses and a rotating chopper wheel located between them. The chopper wheel's speed is adjustable. By controlling the chopper wheel's speed, pulses of appropriate width can be generated at the first HgCdTe detector 10 while also reducing the heating effect of the laser on the detector.

[0039] The first HgCdTe detector 10 is a high-energy radiation detector connected to an oscilloscope for collecting laser time-domain pulse signals. The absorber 11 is used to absorb the amplified pulse laser and part of the detection laser.

[0040] According to an embodiment of the present invention, a measurement process of an apparatus for measuring the temporal gain evolution and relaxation process of CO2 laser amplification includes: a time gating circuit 12 turns on a continuous CO2 laser seed source 1 and a CO2 laser amplifier 6, turns off a short-pulse CO2 laser seed source 2, and after a set time, uses a first mercury cadmium telluride detector 10 to obtain an amplifier gain pulse signal and determine the amplifier gain and the moment of maximum gain; the time gating circuit 12 turns on the short-pulse CO2 laser seed source 2 at the moment of maximum gain, uses a pulsed CO2 laser information detection module 4 to measure the wavelength and pulse width of interference pulse signal light, and the amplified interference pulse signal is reflected by a second thin-film polarizer 7 into an absorber 11. The first mercury cadmium telluride detector 10 obtains the amplifier gain pulse signal after interference to measure the corresponding relaxation process. The set time is a pre-set amplification time.

[0041] When measuring the corresponding relaxation process, the pulse width of the interfering pulse signal light is gradually shortened and the pulse spectrum line is changed.

[0042] Specifically, see Figure 2 , the use process of the device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification is given. The continuous CO2 laser seed source 1 outputs the detection signal light, and the laser system is synchronized with the rotating chopper wheel through the time gating circuit 12. First, the gain evolution is determined in the absence of interference, and the nanosecond pulse laser system is turned off. By properly setting the timing, the amplifier gain pulse signal can be obtained, and the maximum gain moment and the maximum gain can be determined. Then, through timing control and the known gain signal, a high-intensity short pulse (as an interference pulse) is injected into the CO2 laser amplifier 6 at the maximum gain moment, and the interference pulse is separated again by the second thin-film polarizer 7. The recovery of the gain signal after anti-interference can be obtained, and the nanosecond time-domain gain evolution and relaxation process of CO2 laser amplification can be studied. It should be noted that by reducing the nanosecond seed pulse width and changing the pulse spectrum, the relaxation process can be studied in more detail.

[0043] The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification provided by an embodiment of the present invention can track the change in the amplitude of the detection light beam before, during, and after amplification over time, thereby providing a single oscilloscope trace. In addition, a nanosecond short-pulse laser is used as an interference signal, and the polarization direction of the continuous detection laser is perpendicular to the polarization direction of the pulsed light beam. After being combined by a thin-film polarizer, the two beams pass coaxially through the CO2 laser amplifier, thereby tracking the relaxation process occurring on the nanosecond time scale.

[0044] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification, characterized in that: include: A continuous CO2 laser seed source (1), a short pulse CO2 laser seed source (2), and a first beam splitter (3) located on an outgoing light path of the short pulse CO2 laser seed source (2); A pulsed CO2 laser information detection module (4) is located in the transmission light path of the first beam splitter (3); The first thin-film polarizer (5) is located at the intersection of the reflection light path of the first beam splitter (3) and the output light path of the continuous CO2 laser seed source (1); the P-polarized light of the detection signal light generated by the continuous CO2 laser seed source (1) is completely transmitted through the first thin-film polarizer (5), and the S-polarized light of the interference pulse signal light generated by the short-pulse CO2 laser seed source (2) reflected by the first beam splitter (3) is completely reflected by the first thin-film polarizer (5), and then the light is combined and emitted; A CO2 laser amplifier (6), a second thin-film polarizer (7), a second beam splitter (8), a chopper wheel module (9), and a first mercury cadmium telluride detector (10) are sequentially located on an output light path of the first thin-film polarizer (5); an absorber (11) located in the reflection light path of the second thin-film polarizer (7) and the reflection light path of the second beam splitter (8); The time gating circuit (12) is used to control the on / off time of the continuous CO2 laser seed source (1), the short pulse CO2 laser seed source (2) and the CO2 laser amplifier (6).

2. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 1, characterized in that: The detection signal light generated by the continuous CO2 laser seed source (1) uses P-polarized light, and the interference pulse signal light generated by the short-pulse CO2 laser seed source (2) uses S-polarized light.

3. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 1, characterized in that: The short pulse CO2 laser seed source (2) adopts a multi-spectral line short pulse CO2 laser seed source, which is used to generate interference pulse signal light with different spectral lines and different pulse widths.

4. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 1, characterized in that: The chopping wheel module (9) comprises two lenses and a rotating chopping wheel located between the two lenses, wherein the rotation speed of the rotating chopping wheel is adjustable.

5. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 1, characterized in that: The pulsed CO2 laser information detection module (4) comprises a second mercury cadmium telluride detector (41) and a wavelength meter (42), and is used to detect the time domain waveform and wavelength of the output spectrum line of the short pulsed CO2 laser seed source (2).

6. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 1, characterized in that: The CO2 laser amplifier (6) is a radio frequency excited axial fast flow CO2 laser amplifier.

7. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to any one of claims 1 to 6, characterized in that: The measurement process of the device includes: The time gating circuit (12) turns on the continuous CO2 laser seed source (1) and the CO2 laser amplifier (6), turns off the short-pulse CO2 laser seed source (2), and after a set time, uses the first mercury cadmium telluride detector (10) to obtain the amplifier gain pulse signal and determine the amplifier gain and the maximum gain moment; The time gating circuit (12) turns on the short pulse CO2 laser seed source (2) at the maximum gain moment, and uses the pulse CO2 laser information detection module (4) to measure the wavelength and pulse width of the interference pulse signal light. The amplified interference pulse signal is reflected by the second thin film polarizer (7) and enters the absorber (11). The first mercury cadmium telluride detector (10) is used to obtain the gain pulse signal of the amplifier after interference, so as to measure the corresponding relaxation process.

8. The device for measuring the time-domain gain evolution and relaxation process of CO2 laser amplification according to claim 7, characterized in that: When measuring the corresponding relaxation process, the pulse width of the interfering pulse signal light is gradually shortened and the pulse spectrum line is changed.

Images