Multi-channel laser high-precision synchronous measurement device

Abstract

A multi-channel laser high-precision synchronous measurement device includes a transparent scattering sphere, an optical path length adjustment system, a fused silica aspheric lens, a fast photomultiplier tube, an optical fiber, a photodiode, a digital oscilloscope, a single-shot spectrometer, and a computer. This system enables synchronous measurement of multiple ultra-wideband short pulses or multiple narrowband long pulses. The device effectively suppresses the effects of repeatedly moving optical components and mechanical repositioning sampling points for different pulses, effectively improving measurement accuracy, saving time, and increasing measurement efficiency.

Description

Technical Field

[0001] The invention relates to a multi-channel laser high-precision synchronous measuring device. Background Art

[0002] In recent years, with the in-depth study of high-power lasers, laser technology has rapidly developed. High-power lasers are widely used in communications, medicine, industrial production, scientific research, security, energy development, and weapons research. The most typical application in energy development is inertial confinement fusion (ICF). The principle of laser inertial confinement fusion is to uniformly irradiate the surface of a target pellet with high-power laser pulses or laser-generated X-rays. The recoil force generated by the ablation and ejection of target material quickly compresses the deuterium and tritium (DT) gases within the target to a high temperature and high density, achieving sufficient thermonuclear combustion and energy release before the fuel is dispersed, leading to a nuclear fusion reaction. Uniformly driving the target pellet surface requires precise beam synchronization to achieve accurate power balance. Therefore, the multiple laser beams generated and amplified by high-power lasers must be time-synchronized when they reach the target, necessitating a high-precision pulse synchronization measurement system.

[0003] The multi-pulse synchronous measurement systems currently used in high-power laser devices are mainly the following:

[0004] One approach uses fiber array encoding to extract light from a simulated target pellet, which is recorded in separate windows by a streak camera and verified with an X-ray framing camera. The synchronization results achieve a time accuracy better than 10 ps. This method offers high accuracy, but the testing process is complex and inconvenient to operate on large, highly automated targets.

[0005] The second method uses a fast-response photoelectric tube combined with a digital oscilloscope to perform synchronous measurement between pulses. First, photoelectric tubes 1 and 2 are placed simultaneously in front of the target chamber window of the same laser beam, and photoelectric tube 2 is placed in front of the target chamber windows of the remaining laser beams. The resulting time accuracy of the eight laser beams before they reach the target chamber window is also better than 10 ps. This method allows for rapid detection and adjustment, but requires repeated movement of the photoelectric tube, which is relatively inefficient.

[0006] Third, two photoelectric tubes were used to measure the time interval between the reference light path pulse reaching the target point and the reference point. The time interval between the measured light path pulse reaching the target point and the reference point was then measured, with a test accuracy of 25.2 ps. This method has a simple layout and is well suited for real-time adjustments during synchronous measurements. It also offers high measurement efficiency, but the photoelectric tubes must be repositioned during the measurement process, and the accuracy is limited.

[0007] Fourth, time-correlated repetition allows for simultaneous testing and calibration of multiple laser pulses within a single shot, achieving synchronization accuracy better than 30 ps. This method can accurately determine the time synchronization accuracy of 16 lasers within a single shot and perform synchronized optical path adjustment. This method offers high synchronization efficiency and fully utilizes existing equipment. However, it is not suitable for multi-beam laser devices, requiring excessive equipment and lacking in simplicity and directness.

[0008] 5. Utilizing conjugate reflection characteristics, the time difference between the pulse arrival at the target is determined by measuring the time difference between the beam arrival at the two conjugate image points. This approach offers an accuracy of better than 20 ps, ​​shortening test preparation time, enhancing safety, and simplifying operation. It also effectively resolves the pulse overlap problem caused by the high temporal and spatial overlap of laser pulses at the target, enabling precise measurement. However, this approach is subject to device limitations and places high demands on positioning accuracy and device stability.

[0009] These methods have their own advantages, but they cannot simultaneously meet the requirements of simple structure and high measurement accuracy. Therefore, it is necessary to propose a new method that can achieve simple structure, convenient operation, high measurement efficiency, high safety and high accuracy in the target chamber.

[0010] In order to address the shortcomings of these methods, the present invention uses a transparent scattering sphere as a quasi-isotropic scattering source, and designs and verifies the role of a multi-channel laser high-precision synchronous measurement device in improving the time synchronization accuracy of multi-channel laser pulses. The multi-channel laser synchronous measurement technology based on a transparent scattering sphere only places a small ball at the target point in the target chamber, and the collection optical element is fixed at the port position of the target ball, and does not need to be moved repeatedly. Therefore, the device has the advantages of no redundant moving parts, no need to mechanically redirect each light beam with a reflector each time, and high accuracy. The multi-channel laser high-precision synchronous measurement device can not only perform synchronous measurement of narrowband long pulses, but also perform synchronous measurement of ultra-wideband short pulses. It has a wide range of applications and strong practicality. Summary of the Invention

[0011] The present invention aims to improve the synchronization of multiple laser beams reaching a target pellet in a high-power laser device, overcoming the complexities of traditional measurement systems, which require moving optical elements and complex moving parts. A multi-channel laser high-precision synchronization measurement device is provided. Using a transparent scattering sphere and high-precision measurement elements, the system effectively improves the synchronization accuracy of multiple high-power pulses.

[0012] The technical solutions of the present invention are as follows:

[0013] A multi-channel laser high-precision synchronous measurement device is characterized by comprising a beam splitter, an optical path length adjustment system, a transparent scattering sphere, a fused silica aspheric lens, a fast photomultiplier tube, a digital oscilloscope, an optical fiber, a photodiode and a computer;

[0014] The narrowband long pulse is divided into two beams of light by the beam splitter: one is the reference light and the other is the light to be measured. The optical fiber, photodiode and digital oscilloscope are connected in sequence along the transmission direction of the reference light. The optical path length adjustment system, transparent scattering sphere, fused silica aspheric lens, fast photomultiplier tube, digital oscilloscope and computer are placed in sequence along the direction of the light to be measured. The transparent scattering sphere scatters one measuring pulse each time. The digital oscilloscope input channel 1 is connected to the output end of the photodiode, the input channel 2 is connected to the output end of the fast photomultiplier tube, the input end of the photodiode is connected to the output end of the optical fiber, the digital oscilloscope outputs time information to the computer, and the optical path length adjustment system is controlled by computer programming.

[0015] A multi-channel laser high-precision synchronous measurement device is characterized by comprising a beam splitter, an optical path length adjustment system, a transparent scattering sphere, a fused silica aspheric lens, a single-shot spectrometer and the computer;

[0016] An ultra-wideband short pulse is split into two beams of light by the beam splitter: one beam serves as reference light, and the other beam serves as measured light. Optical path length adjustment systems are placed along the transmission directions of the reference light and the measured light, and the two beams of light are simultaneously projected onto a transparent scattering sphere. A fused silica aspheric lens, a single-shot spectrometer, and a computer are then placed. The transparent scattering sphere scatters the two measurement pulses. The single-shot spectrometer imports the obtained interference data into the computer, processes the data, and obtains a delay difference. The delay difference is fed back to the optical path length adjustment system, and optical path adjustment is performed to achieve synchronization between different measurement beams.

[0017] The transparent scattering sphere is mounted on a hard metal rod of the order of 10 μm and placed at the final action point. The holes and grain boundaries of the transparent scattering sphere material act as scattering points, redistributing light incident from any direction into a 4π solid angle.

[0018] The multi-path laser high-precision synchronous measurement device measures multiple narrowband long pulses and multiple ultra-wideband short pulses simultaneously. It measures only one pulse at a time and adjusts the optical path length to compensate for the arrival time difference between the reference and measurement signals. Therefore, the number of optical paths in the test structure can be adjusted as needed.

[0019] The energy of the seed pulse emitted by the laser is 30 mJ, with a repetition frequency of 1 to 5 Hz.

[0020] The optical path length adjustment system is composed of two folding mirrors on a motorized moving platform, which is used to equalize the optical path lengths of all beams.

[0021] The fast photomultiplier tube has a fast rise time of 100 ps.

[0022] The analog bandwidth of the digital oscilloscope is 12 GHz, and the sampling frequency is 40 GS / s.

[0023] The above-mentioned photodiode is an InGaAs photodiode.

[0024] The above spectrometer is a single-shot spectrometer.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1) The use of a transparent scattering sphere enables the multi-channel high-precision laser synchronization measurement device to measure the synchronization accuracy of multiple narrowband long pulses or multiple ultrashort laser pulses. The multi-channel narrowband long pulse synchronization measurement system simultaneously utilizes two optical paths: a measurement optical path consisting of a beam splitter, an optical path length adjustment system, a transparent scattering sphere, a fused silica aspheric lens, a fast photomultiplier tube, and a digital oscilloscope; and a reference optical path consisting of a beam splitter, an optical fiber, a photodiode, and a digital oscilloscope. For each beam, the arrival time difference between the scattered light pulse and the reference pulse is measured. For the synchronous measurement of multiple ultra-wideband short pulses, spectral interferometry is used. One path is selected as the reference. The reference and measurement optical paths are simultaneously projected onto the transparent scattering sphere. The interference light of the two beams is sampled into a single-shot spectrometer, and the delay difference is obtained by inverse Fourier transforming the interference spectrum. The scattering of the transparent scatterer is utilized to redistribute incident light from any direction into a 4π solid angle. The advantage of this is that there is no need to use mirrors inside the target chamber to mechanically redirect each beam. This simple arrangement has no moving parts in a vacuum and does not require mid-process adjustment of the optical elements to ensure measurement of all beams in the upper and lower hemispheres of the target chamber. Therefore, it is simpler, saves more time, and significantly improves efficiency.

[0027] 2) The optical collection element employed is a fused silica aspheric mirror. This mirror captures scattered light from the transparent scattering sphere and collimates it, ensuring uniform imaging on the photocathode of the fast photomultiplier tube and the probe of the single-shot spectrometer. The fused silica aspheric mirror is fixed in place, eliminating the need to move or add additional measurement equipment for multi-channel measurements, resulting in simple operation and high measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural diagram of the multi-channel laser high-precision synchronous measurement device of the present invention.

[0029] Figure 2 This is a workflow diagram for narrow-band long-pulse synchronous measurement using a multi-channel laser high-precision synchronous measurement device.

[0030] Figure 3 This is a workflow diagram for ultra-wideband short pulse synchronous measurement using a multi-channel laser high-precision synchronous measurement device.

[0031] Figure 4 This is a schematic diagram of eight light beams in a multi-channel laser high-precision synchronous measurement device irradiating a transparent scattering sphere through a target chamber. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the embodiments and drawings, but the scope of protection of the present invention should not be limited thereto.

[0033] Please refer to Figure 1 , Figure 1 This is a structural diagram of the multi-channel laser high-precision synchronous measurement device of the present invention. As can be seen from the figure, the multi-channel laser high-precision synchronous measurement device includes a beam splitter 1, an optical path length adjustment system 2, a transparent scattering sphere 3, a fused silica aspheric lens 4, a fast photomultiplier tube 5, a digital oscilloscope 6, an optical fiber 7, a photodiode 8, a single-shot spectrometer 9, and a computer 10.

[0034] See also Figure 2 , Figure 2 This is a workflow diagram for the synchronous measurement of narrow-band long pulses using a multi-channel laser high-precision synchronous measurement device. The beam splitter 1 splits the laser pulses, and the split pulses enter the measurement optical path and the reference optical path respectively. The light to be measured first passes through the optical path length adjustment system 2, and then the light pulse is transmitted to the transparent scattering sphere 3. The incident light pulse to be measured is scattered by the scattering sphere at the center of the target chamber. A portion of the light is captured by the fused aspheric lens 4 and collimated onto the photocathode surface of the fast photomultiplier tube 5. At this time, the light signal is converted into an electrical signal, which is then sent to the digital oscilloscope 6. Another part of the reference pulse is incident on the gradient refractive index fiber 7. The fiber-coupled InGaAs photodiode 8 converts the light pulse into an electrical signal, which is then transmitted to the digital oscilloscope 6. The delay difference between the reference beam and the beam to be measured is read and transmitted to the computer. The optical path length adjustment system is controlled by computer programming, forming a closed-loop synchronous control.

[0035] See also Figure 3 , Figure 3 The following is a workflow diagram for ultra-wideband short pulse synchronous measurement using a multi-channel laser high-precision synchronous measurement device. The measurement utilizes spectral interferometry. First, a beam splitter 1 splits the laser pulses. One pulse is selected as the reference. The reference and measurement beams are emitted simultaneously. Both beams pass through the optical path length adjustment system 2 before impinging on a transparent scattering sphere 3. A fused aspheric lens 4 samples the interference of the scattered light into a single-shot spectrometer 9. The high-precision single-shot spectrometer then imports the acquired interference data into a computer 10. The delay difference is then determined by inverse Fourier transforming the interference spectrum. This delay difference is fed back to the optical path length adjustment system 2, also forming a closed-loop synchronous control.

[0036] See also Figure 4 , Figure 4 This diagram shows eight beams of light illuminating a transparent scattering sphere through a target chamber in a multi-channel high-precision synchronous laser measurement device. When the incident light is a narrowband, long pulse, one beam is selected as the reference beam, and the other as the measurement beam. The reference beam passes sequentially through optical fiber 7, photodiode 8, and digital oscilloscope 6. The light to be measured passes sequentially through optical path length adjustment system 2, transparent scattering sphere 3, fused silica aspheric lens 4, fast photomultiplier tube 5, digital oscilloscope 6, and computer 10. The digital oscilloscope 6 outputs timing information to computer 10, which controls the optical path length adjustment system through programming.

[0037] When the incident light is an ultra-wideband short pulse, a reference beam and a measurement beam are selected from the eight beams. The reference beam and the measurement beam are incident on the transparent scattering sphere 3 located in the center of the target chamber after passing through the optical path length adjustment system 2. The interference light of the scattered light is sampled into the single-shot spectrometer 9 using the fused aspheric lens 4. The interference data is imported into the computer 10, and the delay difference is obtained by inverse Fourier transforming the interference spectrum.

[0038] Whether it is the synchronous measurement of multiple narrowband long pulses or the synchronous measurement of multiple ultra-wideband short pulses, only one pulse beam can be synchronously measured at a time and the optical path is adjusted to compensate for the arrival time difference between the reference signal and the measurement signal.

[0039] This multi-channel laser high-precision synchronous measurement device boasts a simple structure, high accuracy, high measurement efficiency, and excellent stability. The accuracy of synchronized measurement of multiple narrowband long pulses can reach picoseconds, and the accuracy of synchronized measurement of ultra-wideband short pulses can reach femtoseconds. This technology has the advantage of eliminating the need for mirrors to redirect each beam. This simple arrangement, devoid of extra moving parts, simplifies multi-channel measurement without the need to move or add additional measurement equipment, making it easy to operate. This research holds great promise for solving any problem requiring verification of the optical arrival time between two or more laser pulses.

Claims

1. A multi-channel laser high-precision synchronous measurement device, characterized by: The device comprises a beam splitter (1), an optical path length adjustment system (2), a transparent scattering sphere (3), a fused silica aspheric lens (4), a fast photomultiplier tube (5), a digital oscilloscope (6), an optical fiber (7), a photodiode (8), and a computer (10); The narrowband long pulse is divided into two beams of light by the beam splitter (1): one beam is a reference beam, and the other beam is a light to be measured. The optical fiber (7), photodiode (8) and digital oscilloscope (6) are connected in sequence along the transmission direction of the reference light. The optical path length adjustment system (2), transparent scattering sphere (3), fused silica aspheric lens (4), fast photomultiplier tube (5), digital oscilloscope (6) and computer (10) are placed in sequence along the direction of the light to be measured. The transparent scattering sphere (3) scatters one beam of measurement pulse each time. The input channel 1 of the digital oscilloscope (6) is connected to the output end of the photodiode (8), the input channel 2 is connected to the output end of the fast photomultiplier tube (5), the input end of the photodiode (8) is connected to the output end of the optical fiber (7), and the digital oscilloscope (6) is connected to the computer (10) to adjust the optical path length adjustment system (2).

2. A multi-channel laser high-precision synchronous measurement device, characterized by: It includes a beam splitter (1), an optical path length adjustment system (2), a transparent scattering sphere (3), a fused silica aspheric lens (4), a single-shot spectrometer (9) and a computer (10); An ultra-wideband short pulse is split into two beams of light by the beam splitter (1): one beam is used as a reference beam, and the other beam is used as a light to be measured. An optical path length adjustment system (2), a transparent scattering sphere (3), a fused silica aspheric lens (4), a single-shot spectrometer (9), and a computer (10) are placed along the transmission directions of the reference beam and the light to be measured; the transparent scattering sphere (3) scatters each measuring pulse; the single-shot spectrometer (9) imports the obtained interference data into the computer (10), processes the data, and obtains a delay difference, which is fed back to the optical path length adjustment system (2) for optical path adjustment to achieve synchronization between different measuring beams.

3. The multi-channel laser high-precision synchronous measurement device according to claim 1 or 2, characterized in that: The transparent scattering sphere (3) is mounted on a hard metal rod of the order of 10 μm and placed at the final action point. The holes and grain boundaries of the transparent scattering sphere (3) material act as scattering points, redistributing light incident from any direction into a 4π solid angle.

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