Femtosecond laser synchronization device and method based on hollow-core anti-resonant fiber

Abstract

A kind of femtosecond laser synchronization device and method based on hollow-core anti-resonant optical fiber, comprising: first mirror, second mirror, balanced optical cross correlator, first lens, first vacuum chamber, hollow-core anti-resonant optical fiber, second vacuum chamber, second lens, third mirror, fourth mirror, optical delay line and control unit;The time drift of femtosecond laser pulse is measured by balanced optical cross correlator;When balanced cross correlation signal is not zero, there is time drift between two laser pulses, and the amount of drift is indicated by the intensity of balanced cross correlation signal, and the direction of drift is indicated by the positive and negative of cross correlation signal.Correlation signal is transmitted to control unit for processing and generating control signal, and control optical delay line, and balanced optical cross correlation signal is locked to zero, that is, the long-time synchronization of two femtosecond laser pulses is realized by closed-loop feedback control.The present application realizes the long-time synchronization of two femtosecond laser pulses, and can be used in the fields of ultra-short pulse laser synchronization control, ultrafast pump-probe experimental research, etc.

Description

Technical Field

[0001] This invention relates to a femtosecond laser synchronization device and method based on hollow anti-resonant fiber, which can be used in fields such as ultrashort pulse laser synchronization control and ultrafast pump-probe experimental research, and belongs to the field of laser physics and technology. Background Technology

[0002] With the development of the information age, optical fiber has become crucial in modern information and communication due to its advantages such as high transmission speed, low transmission loss, large communication capacity, and readily available and inexpensive raw materials. Laser transmission in space is limited by the position of optical components; therefore, using optical fiber for laser transmission is an effective solution in scenarios requiring flexible laser positioning. For traditional solid-core optical fibers, the wavelength and transmission bandwidth of the laser are limited by the material, and the transmission loss and nonlinearity are relatively large, which greatly limits the transmission distance. Furthermore, the thermal effects that occur when transmitting high-power lasers through solid-core fibers can damage the fiber. With the improvement of microscale optical fiber structure design capabilities and modern fabrication and processing technologies, various microstructured optical fibers have been designed. The emergence of hollow-core antiresonant optical fibers effectively solves the shortcomings of solid-core fibers. Compared with solid-core fibers, they have advantages such as low nonlinearity, low dispersion, low loss, wide transmission window, and transmission speed close to that of air, giving them unparalleled advantages in high-power energy transmission.

[0003] Since the invention of chirped-pulse amplification (CPA) and optical parametric chirped-pulse amplification (OPCPA), the peak power of lasers has reached 10 PW and is moving towards 100 PW. This ultra-high peak power provides extreme physical conditions, ushering in a new era for laser-matter interactions and promoting advancements in strong-field physics, atomic and molecular science, chemistry, and biology. However, environmental factors such as airflow, mechanical vibration, and temperature during long-distance laser transmission affect the relative time delay between laser pulses, leading to significant time drift. This time drift limits experiments requiring high-precision time synchronization, such as ultrafast pump-probe systems. Therefore, designing a high-precision time synchronization system to synchronize different femtosecond lasers is essential. In 2014, Zhang Zhijun et al. proposed a method for synchronizing the delay of ultrashort laser pulses at the femtosecond level (authorization number CN103887693B). This method uses spectral interferometry to control, measure, and monitor the delay between two femtosecond pulses originating from the same source within femtosecond precision. However, spectral interferometry requires a wide laser spectrum, making it impractical for narrowband lasers, and it is more susceptible to variations in laser pulse energy, directional jitter, and spectral changes. In 2015, Cui Yong et al. proposed a measurement device and method for ultrashort pulse time synchronization (authorization number CN105157857B), achieving high-precision time synchronization of two ultrashort pulses based on optical cross-correlation. However, this method is not only susceptible to spatial environmental influences, reducing time synchronization accuracy, but also unsuitable for synchronization measurements in large laser devices operating in long-distance, complex environments because the laser pulses propagate in free space. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a femtosecond laser synchronization device and method based on hollow-core antiresonant fiber. By using hollow-core antiresonant fiber to transmit femtosecond lasers, it is possible to transmit femtosecond lasers under complex conditions and eliminate the influence of the external environment on the femtosecond laser, thereby improving synchronization accuracy. Furthermore, hollow-core antiresonant fiber possesses characteristics such as transmitting high-energy femtosecond lasers and being dispersion-free, which greatly improves the transmission energy of femtosecond lasers and the integration of the synchronization device.

[0005] The purpose of this invention is to provide a femtosecond laser synchronization device and method based on hollow anti-resonant optical fiber.

[0006] To achieve the above-mentioned objectives, the technical solution provided by this invention patent is as follows:

[0007] A femtosecond laser synchronization device based on hollow anti-resonant fiber, characterized in that the synchronization device includes a first mirror, a second mirror, a balanced optical crosscorrelation device, a first lens, a first vacuum chamber, a hollow anti-resonant fiber, a second vacuum chamber, a second lens, a third mirror, a fourth mirror, an optical delay line, and a control unit.

[0008] Two femtosecond laser beams are incident in parallel. The first femtosecond laser beam passes sequentially through an optical delay line, a first mirror, and a second mirror to reach a balanced optical crosscorrelator. The second femtosecond laser beam passes sequentially through a first lens, a first vacuum chamber, a hollow anti-resonant fiber, a second vacuum chamber, a second lens, a third mirror, and a fourth mirror to reach the balanced optical crosscorrelator.

[0009] The optical delay line consists of two mutually perpendicular mirrors placed on a precision translation stage. The precision translation stage is controlled by a translation stage controller to move back and forth along the direction of the incident femtosecond laser, and the delay is controlled by adjusting the optical path of the incident femtosecond laser.

[0010] The balanced optical crosscorrelator includes a beam splitter, a fifth mirror, a transparent material, a first nonlinear crystal, a second nonlinear crystal, a first pinhole aperture, a second pinhole aperture, and a balanced photodetector. Two femtosecond laser beams pass through the beam splitter, and the reflected femtosecond laser beams sequentially pass through the fifth mirror and the first nonlinear crystal to generate frequency-doubled and sum-frequency beams of the two femtosecond laser beams. The first pinhole aperture only allows the sum-frequency beams of the two femtosecond laser beams to pass through and is received by the balanced photodetector. After being transmitted through the beam splitter, the two femtosecond laser beams sequentially pass through the second nonlinear crystal and the second pinhole aperture before entering the balanced photodetector. A transparent material is inserted in the optical path of one of the femtosecond laser beams to provide a delay reference. The two femtosecond laser beams generate their own frequency-doubled and sum-frequency beams after passing through the second nonlinear crystal, and the second pinhole aperture only allows the sum-frequency beams to pass through. Then, the balanced optical crosscorrelator generates a voltage signal based on the intensity of the two sum-frequency beams to determine the time drift of the two femtosecond laser beams.

[0011] The control unit processes the voltage signal of the balanced optical crosscorrelator to form a control signal, which is then transmitted to the precision translation stage to control the movement of the optical delay line and correct the time drift between the two femtosecond laser beams.

[0012] The nonlinear crystals mentioned include, but are not limited to, barium metaphosphate (BBO), potassium dihydrogen phosphate (KDP), lithium triborate (LBO), and deuterated potassium dihydrogen phosphate (DKDP);

[0013] The transparent material includes, but is not limited to, calcium fluoride or glass, and the control unit includes a data acquisition card and a feedback control program.

[0014] A method for synchronizing two femtosecond laser beams using the aforementioned synchronization device comprises the following five steps:

[0015] Step 1: Complete the optical path setup according to the schematic diagram of the synchronization device (see...) Figure 1 );

[0016] Step 2: The first femtosecond laser beam passes sequentially through the optical delay line, the first mirror, and the second mirror into the balanced optical crosscorrelator. The second femtosecond laser beam is focused by the first lens and coupled into a hollow anti-resonant fiber. One end of the hollow anti-resonant fiber is placed in the first vacuum chamber, and the other end is placed in the second vacuum chamber. It is then collimated by the second lens and enters the balanced optical crosscorrelator through the third and fourth mirrors. The function of the first and second vacuum chambers is to evacuate the inside of the hollow anti-resonant fiber to a vacuum state.

[0017] Step 3: The two femtosecond laser beams entering the balanced optical cross-correlator are reflected by the beam splitter and pass through the first nonlinear crystal in a non-collinear manner via the fifth mirror. After passing through the first nonlinear crystal, the two femtosecond laser beams generate their respective frequency-doubled and sum-frequency beams. After the fundamental and frequency-doubled beams are filtered out by the first pinhole aperture, the sum-frequency beam is incident on the balanced photodetector. The transmission portions of the two femtosecond laser beams also pass through the second nonlinear crystal in a non-collinear manner, generating their respective frequency-doubled and sum-frequency beams. A transparent material is placed in the optical path of one of the femtosecond laser beams, introducing a fixed delay as a time drift reference. After the fundamental and frequency-doubled beams are filtered out by the second pinhole aperture, the sum-frequency beam is incident on the balanced photodetector. Using a non-collinear configuration for the two femtosecond laser beams makes it easier to achieve phase matching and also allows for the spatial separation of the frequency-doubled and sum-frequency beams.

[0018] Step 4: The balanced optical detector converts the intensity of the two sum-frequency beams into voltage signals and subtracts them. If the voltage signal output by the balanced optical detector is zero, it indicates that the time drift between the two femtosecond laser beams is zero. When there is a time drift between the two femtosecond laser beams, the output voltage of the balanced optical detector is not zero. The voltage signal output by the balanced optical detector is transmitted to the control unit for processing and generation of control signals. The precision translation stage moves forward or backward along the direction of femtosecond laser transmission according to the control signals. The optical delay line placed on the precision translation stage increases or decreases the optical path of the femtosecond laser to maintain the zero output state of the balanced optical detector. That is, the synchronization of the two femtosecond laser beams is achieved through closed-loop feedback control.

[0019] Step 5: When the control unit is not turned on, record the change in the output voltage signal of the balanced optical detector. When the self-made control unit is turned on, record the change in the output voltage signal of the balanced optical detector again to determine the time synchronization accuracy of the two femtosecond laser beams.

[0020] Compared with prior art, the present invention has the following significant advantages:

[0021] 1. This invention uses hollow-core anti-resonant optical fiber to transmit high-energy femtosecond lasers, which not only eliminates time drift caused by factors such as airflow, mechanical vibration, and temperature in free space, thus improving the accuracy of synchronous measurement and correction, but also enables flexible transmission of femtosecond lasers, freeing it from the limitations of the position of components such as mirrors and lenses when transmitting femtosecond lasers in free space.

[0022] 2. By adding vacuum chambers at both ends of the hollow anti-resonant fiber, this invention can ensure that the hollow anti-resonant fiber is in a vacuum state. This eliminates the need for additional dispersion compensation devices and avoids the influence of material dispersion on femtosecond lasers, greatly improving the transmission energy and the integration of the synchronization device.

[0023] 3. This invention has the ability to measure and correct time drift between femtosecond lasers over long periods of time, which is of great significance for real-time synchronization of laser devices with long-distance transmission.

[0024] 4. This invention enables convenient transmission of high-power femtosecond lasers and eliminates time drift caused by external environmental factors, which has significant practical value and application prospects. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a femtosecond laser synchronization device based on hollow anti-resonant optical fiber according to the present invention.

[0026] Figure 2 This is a schematic diagram of a balanced optical cross-correlator.

[0027] Figure 3 This is a schematic diagram of the time drift of two femtosecond laser beams in an open-loop state within 90 minutes.

[0028] Figure 4 This is a schematic diagram of time drift correction between two femtosecond laser beams in a closed-loop state within 90 minutes. Detailed Implementation

[0029] The present invention will be further illustrated by the following embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0030] Please see Figure 1 , Figure 1 It is a femtosecond laser synchronization device based on hollow anti-resonant fiber. The synchronization device includes an optical delay line 101, a first reflector 102, a second reflector 103, a balanced optical crosscorrelator 104, a control unit 105, a first lens 106, a first vacuum chamber 107, a hollow anti-resonant fiber 108, a second vacuum chamber 109, a second lens 110, a third reflector 111, and a fourth reflector 112.

[0031] Two femtosecond laser beams are incident in parallel. The first femtosecond laser beam passes sequentially through an optical delay line 101, a first reflector 102, and a second reflector 103 before reaching a balanced optical crosscorrelator 104. The second femtosecond laser beam passes sequentially through a first lens 106, a first vacuum chamber 107, a hollow-core anti-resonant fiber 108, a second vacuum chamber 109, a second lens 110, a third reflector 111, and a fourth reflector 112 before entering the balanced optical crosscorrelator 104. The time drift between the two femtosecond laser beams is measured by the balanced optical crosscorrelator 104, and the control unit 105 controls the optical delay line 101 to correct the time drift of the two femtosecond laser beams in real time.

[0032] The aforementioned optical delay line 101 consists of two mutually perpendicular mirrors placed on a precision translation stage. After passing through the optical delay line 101, the incident femtosecond laser is emitted parallel to the direction of the incident femtosecond laser. The precision translation stage is controlled by a translation stage controller to move back and forth along the direction of the incident femtosecond laser. By adjusting the optical path of the incident femtosecond laser, the time delay of the two femtosecond laser beams is adjusted, thereby achieving the purpose of correcting the time drift of the two femtosecond laser beams.

[0033] Please refer to Figure 2 The aforementioned balanced optical crosscorrelation device 104 includes a beam splitter 201, a fifth reflector 202, a first nonlinear crystal 203, a first pinhole aperture 204, a balanced photodetector 205, a transparent material 206, a second nonlinear crystal 207, and a first pinhole aperture 208. The two femtosecond laser beams pass through the beam splitter 201, and the reflected femtosecond laser beams pass through the fifth reflector 202 and are incident on the first nonlinear crystal 203 in a non-collinear manner. After passing through the first nonlinear crystal 203, the two femtosecond laser beams generate their own frequency-doubled light and sum-frequency light. The first pinhole aperture 204 filters out the frequency-doubled light of the two femtosecond laser beams, allowing only the sum-frequency light to pass through and be incident on the balanced photodetector 205.

[0034] The two femtosecond laser beams, after being transmitted through beam splitter 201, are incident on the second nonlinear crystal 207 in a non-collinear manner, generating frequency-doubled and sum-frequency beams. The second pinhole aperture 208 filters out the frequency-doubled beam, allowing the sum-frequency beam to pass through and be incident on the balanced photodetector 205. A transparent material 206 is inserted into the optical path of one of the femtosecond laser beams to provide a delay reference. Then, the balanced optical cross-correlation device 205 converts the difference between the intensities of the two sum-frequency beams into a voltage signal, which is the cross-correlation signal. The time drift of the two femtosecond laser beams can be measured using the cross-correlation signal. The cross-correlation signal is transmitted electrically to the control unit 105 to generate a control signal. This control signal can control the movement of the optical delay line 101 to correct the time drift of the two femtosecond laser beams in real time, achieving synchronization of the two femtosecond laser beams.

[0035] The method for achieving time synchronization of two femtosecond laser beams will be further explained below using the aforementioned synchronization device.

[0036] Step 1: Complete the optical path setup according to the schematic diagram of the synchronization device (see...) Figure 1 ).

[0037] Step 2: The first femtosecond laser beam passes sequentially through the optical delay line, the first mirror, and the second mirror into the balanced optical crosscorrelator. The second femtosecond laser beam is focused by the first lens and coupled into a hollow anti-resonant fiber. One end of the hollow anti-resonant fiber is placed in the first vacuum chamber, and the other end is placed in the second vacuum chamber. It is then collimated by the second lens and enters the balanced optical crosscorrelator through the third and fourth mirrors. The function of the first and second vacuum chambers is to evacuate the interior of the hollow anti-resonant fiber to a vacuum state.

[0038] Step 3: The two femtosecond laser beams entering the balanced optical cross-correlator are reflected by the beam splitter and pass through the first nonlinear crystal in a non-collinear manner via the fifth mirror. After passing through the first nonlinear crystal, the two femtosecond laser beams generate their respective frequency-doubled and sum-frequency beams. After the fundamental and frequency-doubled beams are filtered out by the first pinhole aperture, the sum-frequency beam is incident on the balanced photodetector. The transmission portions of the two femtosecond laser beams also pass through the second nonlinear crystal in a non-collinear manner, generating their respective frequency-doubled and sum-frequency beams. A transparent material is placed in the optical path of one of the femtosecond laser beams, introducing a fixed delay as a time drift reference. After the fundamental and frequency-doubled beams are filtered out by the second pinhole aperture, the sum-frequency beam is incident on the balanced photodetector. Using a non-collinear configuration for the two femtosecond laser beams makes it easier to achieve phase matching and also allows for the spatial separation of the frequency-doubled and sum-frequency beams.

[0039] Step 4: The balanced optical detector converts the intensity of the two sum-frequency beams into voltage signals and subtracts them. If the voltage signal output by the balanced optical detector is zero, it indicates that the time drift between the two femtosecond laser beams is zero. When there is a time drift between the two femtosecond laser beams, the output voltage of the balanced optical detector is not zero. The voltage signal output by the balanced optical detector is transmitted to the control unit for processing and generation of a control signal. The precision translation stage moves forward or backward along the direction of femtosecond laser transmission according to the control signal. The optical delay line placed on the precision translation stage increases or decreases the optical path of the femtosecond laser to maintain the zero output state of the balanced optical detector. That is, the synchronization of the two femtosecond laser beams is achieved through closed-loop feedback control.

[0040] Step 5: When the control unit is not turned on, record the change in the output voltage signal of the balanced optical detector, such as... Figure 3As shown, the time drift of the two femtosecond laser beams varied irregularly and drastically within 90 minutes, with a root mean square error (RMS) of 5.23 fs. When the self-made control unit was activated, the changes in the output voltage signal of the balanced optical detector were recorded again to determine the time synchronization accuracy of the two femtosecond laser beams. Figure 4 As shown, the root mean square error (RMS) of the time drift of the two femtosecond laser beams decreased to 2.51 fs within 90 minutes. This result demonstrates that the synchronization device and method of the present invention effectively achieve the goal of synchronizing two femtosecond laser beams. By using hollow-core anti-resonant fiber, the jitter caused by the external environment is eliminated, improving the synchronization accuracy. This has significant implications for research fields such as high-energy femtosecond laser transmission, ultrashort pulse laser synchronization control, and ultrafast pump-probe experiments.

Claims

1. A femtosecond laser synchronization device based on hollow-core anti-resonant fiber, characterized in that, It includes a first reflector, a second reflector, a balanced optical crosscorrelator, a first lens, a first vacuum chamber, a hollow-core anti-resonant fiber, a second vacuum chamber, a second lens, a third reflector, a fourth reflector, an optical delay line, and a control unit; one end of the hollow-core anti-resonant fiber is placed in the first vacuum chamber, and the other end is placed in the second vacuum chamber, the first vacuum chamber and the second vacuum chamber are used to evacuate the interior of the hollow-core anti-resonant fiber to a vacuum state; Two femtosecond laser beams are incident in parallel. The first femtosecond laser beam passes sequentially through the optical delay line, the first mirror, and the second mirror before being incident on the balanced optical cross-correlator. The second femtosecond laser beam passes sequentially through the first lens, the first vacuum chamber, the hollow anti-resonant fiber, the second vacuum chamber, the second lens, the third mirror, and the fourth mirror before being incident on the balanced optical cross-correlator. The balanced optical crosscorrelator measures the time drift between the two femtosecond laser beams and transmits it to the control unit, which controls the optical delay line to correct the time drift between the two femtosecond laser beams in real time. The balanced optical detector converts the intensity of the two sum-frequency beams into voltage signals and subtracts them. If the voltage signal output by the balanced optical detector is zero, the time drift between the two femtosecond laser beams is zero; otherwise, there is a time drift between the two femtosecond laser beams. The optical delay line consists of two mutually perpendicular mirrors placed on a precision translation stage. The precision translation stage is controlled by a translation stage controller to move back and forth along the direction of the incident femtosecond laser, thereby adjusting the optical path length of the incident femtosecond laser to control the delay.

2. The femtosecond laser synchronization device based on hollow antiresonant fiber according to claim 1, characterized in that, The balanced optical detector transmits the output voltage signal to the control unit for processing and generates a control signal. The precision translation stage moves forward or backward along the direction of femtosecond laser transmission according to the control signal. The optical delay line placed on the precision translation stage increases or decreases the optical path of the femtosecond laser to maintain the zero output state of the balanced optical detector. That is, the synchronization of the two femtosecond lasers is achieved through closed-loop feedback control.

3. The femtosecond laser synchronization device based on hollow antiresonant fiber according to claim 1, characterized in that, The balanced optical cross-correlator includes a beam splitter, a fifth mirror, a transparent material, a first nonlinear crystal, a second nonlinear crystal, a first pinhole aperture, a second pinhole aperture, and a balanced photodetector. The two femtosecond laser beams, after being reflected by the beam splitter, are reflected by the fifth mirror and then incident on the first nonlinear crystal in a non-collinear manner, generating frequency-doubled light and sum-frequency light of the two femtosecond laser beams respectively. The frequency-doubled light of the two femtosecond laser beams is filtered out by the first pinhole aperture, and the sum-frequency light passes through and is incident on the balanced photodetector. The two femtosecond laser beams are transmitted through the beam splitter. One of the beams is delayed by a transparent material. The two transmitted beams are incident on the second nonlinear crystal in a non-collinear manner to generate their respective frequency-doubled light and sum-frequency light. The frequency-doubled light is filtered out by the second pinhole aperture, and the sum-frequency light passes through and is incident on the balanced photodetector. The balanced optical cross-correlator converts the difference between two sum-frequency light intensities into a voltage signal, which is the cross-correlation signal. The time drift of two femtosecond laser beams can be measured through the cross-correlation signal.

4. A femtosecond laser synchronization device based on hollow antiresonant fiber according to claim 3, characterized in that, The cross-correlation signal is transmitted to the control unit via electrical means. The control unit processes the voltage signal of the balanced optical cross-correlation device to form a control signal. The control signal is transmitted to the precision translation stage to control the movement of the optical delay line, correct the time drift between the two femtosecond laser beams, and achieve the purpose of synchronizing the two femtosecond laser beams.

5. A femtosecond laser synchronization device based on hollow antiresonant fiber according to claim 3, characterized in that, The first nonlinear crystal and the second nonlinear crystal are barium metaphosphate (BBO), potassium dihydrogen phosphate (KDP), lithium triborate (LBO), or deuterated potassium dihydrogen phosphate (DKDP).

6. A femtosecond laser synchronization device based on hollow antiresonant fiber according to claim 3, characterized in that, The transparent material is calcium fluoride or glass, and the control unit includes a data acquisition card and a feedback control program.

7. A femtosecond laser synchronization method based on hollow-core anti-resonant fiber, characterized in that, Includes the following steps: Construct a femtosecond laser synchronization device based on hollow anti-resonant fiber as described in any of claims 1-6; The first femtosecond laser beam passes sequentially through an optical delay line, a first mirror, and a second mirror into a balanced optical cross-correlator; the second femtosecond laser beam is focused by a first lens and then coupled into a hollow anti-resonant fiber. Two femtosecond laser beams entering the balanced optical cross-correlator are reflected by a beam splitter and pass through a first nonlinear crystal in a non-collinear manner via a fifth mirror. After passing through the first nonlinear crystal, the two femtosecond laser beams generate their own frequency-doubled and sum-frequency beams. After the fundamental and frequency-doubled beams are filtered out by a first pinhole aperture, the sum-frequency beam is incident on a balanced photodetector. Similarly, the transmission portions of the two femtosecond laser beams pass through a second nonlinear crystal in a non-collinear manner, generating their own frequency-doubled and sum-frequency beams. A transparent material is placed in the optical path of one of the femtosecond laser beams, introducing a fixed delay as a time drift reference. After the fundamental and frequency-doubled beams are filtered out by a second pinhole aperture, the sum-frequency beam is incident on a balanced photodetector. The non-collinear arrangement of the two femtosecond laser beams makes it easier to achieve phase matching and allows for the separation of the frequency-doubled and sum-frequency beams in space. The balanced optical detector converts the intensity of two sum-frequency beams into voltage signals and subtracts them. If the voltage signal output by the balanced optical detector is zero, it means that the time drift between the two femtosecond laser beams is zero. When there is a time drift between the two femtosecond laser beams, the output voltage of the balanced optical detector is not zero. The voltage signal output by the balanced optical detector is transmitted to the control unit for processing and generating a control signal. The precision translation stage moves forward or backward along the direction of femtosecond laser transmission according to the control signal. The optical delay line placed on the precision translation stage increases or decreases the optical path of the femtosecond laser to maintain the zero output state of the balanced optical detector. That is, the synchronization of the two femtosecond laser beams is achieved through closed-loop feedback control. When the control unit is not turned on, the change in the output voltage signal of the balanced optical detector is recorded. When the self-made control unit is turned on, the change in the output voltage signal of the balanced optical detector is recorded again to determine the time synchronization accuracy of the two femtosecond laser beams.

Images