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CN-122026213-A - Femtosecond laser pulse compression system with compact structure and adjustable pulse width

CN122026213ACN 122026213 ACN122026213 ACN 122026213ACN-122026213-A

Abstract

The application provides a femtosecond laser pulse compression system with a compact structure and adjustable pulse width, which relates to the technical field of femtosecond lasers, and comprises a seed source, a pulse stretcher, an amplifying chain and a pulse compression device sequentially along a light path, wherein the pulse compression device comprises a polarization beam splitting unit, an electro-optic polarization modulation unit, a single compressed grating and a light path turning-back unit; the polarization state of the light beam is dynamically switched by applying a voltage signal with a specific time sequence to the electro-optical polarization modulation unit, so that the light beam is selectively controlled to complete round-trip transmission for a preset number of times in the multi-channel folding compression light path in different polarization states, and the compression ratio of laser pulses and the continuous adjustment of the output pulse width are realized. On the premise of ensuring large-broadening-amount matching, the system is extremely compact, and the pulse width is continuously and flexibly electrically controlled.

Inventors

  • HU MINGLIE
  • HAO JINGYU
  • LIU BOWEN

Assignees

  • 天津大学

Dates

Publication Date
20260512
Application Date
20260414

Claims (9)

  1. 1. A femtosecond laser pulse compression system with compact structure and adjustable pulse width, which sequentially comprises a seed source (1), a pulse stretcher (2), an amplifying chain and a pulse compression device (15) along an optical path, The pulse compression device (15) comprises a polarization beam splitting unit, an electro-optic polarization modulation unit (9), a single compressed grating (11) and an optical path turning-back unit; Wherein the polarization light splitting unit, the electro-optical polarization modulation unit (9), the single compressed grating (11) and the light path turning-back unit jointly form a multi-channel folding compressed light path; The polarization state of the light beam is dynamically switched by applying a voltage signal with a specific time sequence to the electro-optic polarization modulation unit (9), so that the light beam is selectively controlled to finish round trip transmission for a preset number of times in the multi-channel folding compression light path in different polarization states, and the compression ratio of the laser pulse and the continuous adjustment of the output pulse width are realized; The device further comprises a control unit (14) and a pulse width diagnosis module (13), wherein the control unit (14) is configured for: receiving a target pulse width parameter; Generating a corresponding voltage control time sequence signal according to the target pulse width parameter and sending the voltage control time sequence signal to the electro-optic polarization modulation unit (9); Acquiring an actual output pulse width measured by the pulse width diagnosis module (13); Adjusting the voltage control timing signal according to the difference between the actual output pulse width and the target pulse width parameter; Iteratively performing steps such that the actual output pulse width approaches the target pulse width parameter.
  2. 2. The femtosecond laser pulse compression system with compact structure and adjustable pulse width according to claim 1, wherein the electro-optical polarization modulation unit (9) is a pockels cell which introduces pi/2 phase delay in the beam by applying or canceling a quarter wave voltage to switch the polarization state of the beam.
  3. 3. The compact and pulse width adjustable femtosecond laser pulse compression system as set forth in claim 1, wherein the optical path turning-back unit includes: A first zero degree mirror (10), wherein the first zero degree mirror (10) is arranged on an output light path of the electro-optic polarization modulation unit (9) and is positioned between the electro-optic polarization modulation unit (9) and the monolithic compressed grating (11) and is used for reflecting a light beam from the electro-optic polarization modulation unit (9) back to the monolithic compressed grating (11); and the second zero-degree reflecting mirror (12) is arranged on the diffraction light path of the single compressed grating (11) and is used for returning the light beam diffracted by the single compressed grating (11) along the original path.
  4. 4. The compact and pulse width adjustable femtosecond laser pulse compression system of claim 1 wherein the predetermined number of times is an integer multiple of 4, by controlling the timing of the voltage signal, the beam is passed through the monolithic compression grating (11) an integer multiple of 4 to match different amounts of system spread.
  5. 5. The femtosecond laser pulse compression system with compact structure and adjustable pulse width according to claim 1, wherein the system is based on pulse chirping amplification technology, and the amplification chain comprises an optical fiber amplifier (3) and a solid state amplifier (4) which are sequentially arranged and used for amplifying the widened pulse in multiple stages.
  6. 6. The femtosecond laser pulse compression system with compact structure and adjustable pulse width according to claim 1, wherein a polarization control module is further arranged between the amplifying chain and the pulse compression device (15), and the polarization control module comprises a second polarization spectroscope (5), a half wave plate (6) and a faraday rotator (7) which are sequentially arranged in an optical path and used for adjusting the polarization state of a light beam entering the pulse compression device (15).
  7. 7. The femtosecond laser pulse compression system with compact structure and adjustable pulse width according to claim 6, wherein the compressed light beam is reflected from the polarization beam splitting unit in a vertical polarization state, is converted into a horizontal polarization state again through the electro-optical polarization modulation unit (9) and the optical path turning-back unit, returns to the polarization beam splitting unit and is transmitted, and sequentially passes through the faraday rotator (7) and the half wave plate (6), the polarization state of which is maintained or adjusted to be horizontal polarization, and is finally output by the second polarization beam splitter (5).
  8. 8. The compact and pulse width adjustable femtosecond laser pulse compression system as recited in claim 1, wherein the control unit (14) is further configured to: invoking a system response model characterizing a relationship between the voltage control timing signal and a corresponding output pulse width; when the voltage control time sequence signal is adjusted in each iteration, the system response model and the current actual output pulse width measured value are combined, and the target voltage time sequence required by reaching the target pulse width parameter is predicted; The target voltage sequence is used as a voltage control sequence signal sent to the electro-optic polarization modulation unit (9) in the next iteration.
  9. 9. The compact and pulse width adjustable femtosecond laser pulse compression system as recited in claim 8, wherein the control unit (14) is further configured to: Continuously recording a historical data set formed by the voltage control time sequence signal, the actual output pulse width measured value and the corresponding system state parameter in the running process of the system; And periodically updating the system response model based on the historical data set so as to dynamically adapt the model to system characteristic changes, wherein the system state parameters comprise ambient temperature, pump power of the amplifying chain and/or central wavelength drift amount of the seed source (1).

Description

Femtosecond laser pulse compression system with compact structure and adjustable pulse width Technical Field The invention belongs to the technical field of femtosecond lasers, and particularly relates to a femtosecond laser pulse compression system which is compact in structure and adjustable in pulse width. Background The ultra-high peak power and ultra-short pulse duration of the femtosecond laser make the femtosecond laser have unique advantages in the fields of high-precision processing, semiconductor manufacturing, national defense safety and the like. The output of the femtosecond laser is typically achieved using a pulse chirped amplification (CPA) technique. To achieve higher peak power and shorter pulse output, a larger amount of spread is typically required to meet the demands of CPA technology. However, in the laser technical field, a larger broadening amount often needs a farther grating pair pitch to achieve ideal matching, and the farther grating pair pitch increases the volume of the femtosecond laser, reduces the space utilization, and reduces the stability of the laser. The structure of the laser still remains compact under the premise that the prior art cannot meet the requirements of larger stretching quantity and grating pair spacing. At present, in order to effectively reduce the grating pair spacing, a pulse compressor and a femtosecond pulse laser scheme disclosed in patent number 201920398416.1 are generally adopted, a single grating and two reflectors are utilized to turn back an optical path, so that the stretched pulse light passes through the grating four times, the compression distance is effectively shortened to be half of that of a double grating, and the purpose of compact structure of the laser is realized. However, for a system with a large widening amount, the solution still needs a long space to compress the optical path, which leads to an increase in the volume of the device, and the laser cavity is easy to generate stress, so that the stability is reduced. In addition, in order to ensure the stability of the system, the traditional scheme adopts a fixed mechanical structural member, the compressed pulse width is constant and is not tunable, and the space compressor is difficult to realize flexible adaptation when facing application scenes with different pulse width requirements, and has a certain limitation on an application level. In order to overcome the defects of the prior art, the problems of large laser volume, serious cavity shape, poor stability and difficult adjustment of pulse width caused by long compression distance aiming at a femtosecond laser system with large broadening quantity are solved. The invention provides a pulse compression system which is compact in structure and high in stability and adjustable in pulse width. Disclosure of Invention In view of the above-mentioned defects or shortcomings in the prior art, a femto second laser pulse compression system with compact structure and adjustable pulse width is provided, which sequentially comprises a seed source, a pulse stretcher, an amplifying chain and a pulse compression device along an optical path, wherein the pulse compression device comprises a polarization beam splitting unit, an electro-optic polarization modulation unit, a monolithic compression grating and an optical path turning-back unit; the polarization light splitting unit, the electro-optical polarization modulation unit, the single compressed grating and the light path turning-back unit form a multi-channel folding compressed light path together; The polarization state of the light beam is dynamically switched by applying a voltage signal with a specific time sequence to the electro-optic polarization modulation unit, so that the light beam is selectively controlled to finish round trip transmission for a preset number of times in the multi-channel folding compression light path in different polarization states, and the compression ratio of the laser pulse and the continuous adjustment of the output pulse width are realized; The pulse width diagnosis device further comprises a control unit and a pulse width diagnosis module, wherein the control unit is configured to: receiving a target pulse width parameter; Generating a corresponding voltage control time sequence signal according to the target pulse width parameter and sending the voltage control time sequence signal to the electro-optic polarization modulation unit; acquiring the actual output pulse width measured by the pulse width diagnosis module; Adjusting the voltage control timing signal according to the difference between the actual output pulse width and the target pulse width parameter; Iteratively performing steps such that the actual output pulse width approaches the target pulse width parameter. According to the technical scheme provided by the application, the electro-optical polarization modulation unit is a Prkerr box, and the Prkerr box introduces pi/2 phase delay