A device for generating ultrafast laser pulse trains based on Fabry-Perot cavity

Abstract

The present invention discloses a device for generating an ultrafast laser pulse sequence based on a Fabry-Perot resonant cavity, comprising a half-wave plate, an optical path deflection device, a first laser pulse sequence generating device and a second laser pulse sequence generating device. Based on the characteristics of the Fabry-Perot resonant cavity, the present invention designs the first and second laser pulse sequence generating devices, and respectively arranges them in the horizontal optical path direction and the vertical optical path direction of the optical path deflection device; the pulse sequence emitted by the first laser pulse sequence generating device is introduced into the second laser pulse sequence generating device, so that each sub-pulse further forms a sub-pulse sequence. By adjusting the cavity length of the two laser pulse sequence generating devices, the number of effective pulses is greatly increased while ensuring the energy utilization rate, and the time interval of the pulse sequence is adjusted over a wide range. The present invention has the advantages of simple structure, large adjustable range of sub-pulse sequence time interval, large number of effective pulses and high energy output efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of ultrafast laser pulse modulation, in particular to a device for generating ultrafast laser pulse sequences based on a Fabry-Perot resonant cavity. Background Art

[0002] Ultrafast lasers have the characteristics of short duration and high peak power. When interacting with materials, they can greatly improve the processing quality while suppressing thermal effects. Therefore, ultrafast laser processing has important applications in high-precision fields such as micro-nano structure manufacturing and nano-bioengineering. In recent years, with the rapid development of ultrafast laser technology, the pulse energy and power of ultrafast lasers have increased rapidly, and the processing speed has increased accordingly. However, high pulse energy and high power ultrafast laser processing can easily cause material cracking and melt splashing, which seriously affects the quality of ultrafast laser processing. Ultrafast laser pulse time-domain shaping based on the principle of ablation cooling modulates the ultrafast laser into a laser pulse sequence with intervals of femtoseconds to nanoseconds, which can effectively improve processing efficiency, reduce residual heat effects of ablation, and improve processing quality. Therefore, people have developed a variety of methods to perform time-domain modulation on ultrafast lasers.

[0003] In the prior art, the first method is to use a 4f structure pulse shaping system based on a spatial light modulator to generate a time-domain shaped ultrafast laser, which can perform different phase delays on each pixel unit on the spatial light modulator, thereby obtaining a laser pulse sequence with adjustable sub-pulse interval and adjustable sub-pulse energy. This method has a flexible modulation mode, but is limited by the pixel unit of the spatial light modulator. The sub-pulse interval is usually less than 20 ps, ​​and the processing effect cannot be optimized. In addition, this method has a very high system cost, poor stability, and difficulty in adjustment, making it difficult to promote industrially.

[0004] The second method is to use the Michelson interferometer-based spectrometry method to expand the double-pulse sequence into multiple laser pulse sequences by cascading multiple Michelson interferometer-like structures. However, the optical path structure of this method is very complex and the energy ratio is difficult to adjust.

[0005] The third method is a pulse train modulation method based on the Fabry-Perot resonant cavity. The ultrafast laser is reflected and transmitted back and forth between a pulse train modulator composed of two modulation lenses coated with semi-transparent and semi-reflective films. A laser pulse sequence with adjustable pulse interval and energy ratio can be obtained. However, the output laser pulse sequence is the transmitted light of the Fabry-Perot cavity, and the energy output efficiency is low, only about 7%, which greatly limits the application of the Fabry-Perot cavity.

[0006] In summary, the time-frequency domain pulse shaping method in the prior art has the disadvantages of high cost, complex optical path structure, low energy utilization and small number of effective pulses. Summary of the invention

[0007] The purpose of the present invention is to provide a device for generating ultrafast laser pulse sequences based on a Fabry-Perot resonant cavity in response to the deficiencies of the prior art. Based on the characteristics of the Fabry-Perot resonant cavity, the present invention designs a first and a second laser pulse sequence generating device, and respectively sets them in the horizontal optical path direction and the vertical optical path direction of the optical path deflection device; the pulse sequence emitted by the first laser pulse sequence generating device is introduced into the second laser pulse sequence generating device, so that each sub-pulse further forms a sub-pulse sequence. By adjusting the cavity length of the two laser pulse sequence generating devices, the number of effective pulses can be greatly increased while ensuring the energy utilization rate, and the time interval of the pulse sequence can be adjusted over a wide range. The present invention has the advantages of simple structure, a large adjustable range of the sub-pulse sequence time interval, a large number of effective pulses, and high energy output efficiency.

[0008] The specific technical solution for achieving the purpose of the present invention is:

[0009] A device for generating an ultrafast laser pulse sequence based on a Fabry-Perot resonant cavity, which features include a half-wave plate, an optical path deflection device, a first laser pulse sequence generating device and a second laser pulse sequence generating device;

[0010] The optical path deflection device is composed of a polarization beam splitter cube, a first quarter wave plate and a second quarter wave plate; the polarization beam splitter cube and the first quarter wave plate are connected in sequence along a horizontal optical path, and the polarization beam splitter cube and the second quarter wave plate are connected in sequence along a vertical optical path;

[0011] The first laser pulse sequence generating device is composed of a first flat beam splitter and a first zero-degree total reflector; the first flat beam splitter and the first zero-degree total reflector are sequentially connected along a horizontal optical path;

[0012] The second laser pulse sequence generating device is composed of a second flat beam splitter and a second zero-degree total reflection mirror; the second flat beam splitter and the second zero-degree total reflection mirror are sequentially connected along a vertical optical path;

[0013] The half-wave plate, the optical path deflection device and the first laser pulse sequence generating device are sequentially arranged in the horizontal direction, wherein the half-wave plate and the polarization beam splitter cube of the optical path deflection device and the first quarter-wave plate of the optical path deflection device and the first flat beam splitter of the first laser pulse sequence generating device are sequentially connected along the horizontal optical path;

[0014] The optical path deflecting device and the second laser pulse sequence generating device are sequentially arranged along the vertical direction, wherein the second quarter wave plate of the optical path deflecting device and the second flat beam splitter of the second laser pulse sequence generating device are sequentially connected along the vertical optical path.

[0015] The transmission and reflection ratios of the first flat beam splitter are: 1:9, 2:8, 3:7, 4:6 or 5:5.

[0016] The transmission and reflection ratios of the second flat beam splitter are: 1:9, 2:8, 3:7, 4:6 or 5:5.

[0017] The distance d between the first flat beam splitter and the first zero-degree total reflection mirror of the first laser pulse sequence generating device is adjustable, and the adjustable range is: 0.15-225 mm.

[0018] The distance D between the second flat beam splitter and the second zero-degree total reflection mirror of the second laser pulse sequence generating device is adjustable, and the adjustable range is: 0.15-450 mm.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects and advantages:

[0020] The present invention retains the advantages of the Fabry-Perot resonant cavity, and designs the second beam splitter in the cavity as a zero-degree total reflection mirror, that is, the first laser pulse sequence generating device of the present invention is composed of a first flat beam splitter and a first zero-degree total reflection mirror, the first flat beam splitter and the first zero-degree total reflection mirror are sequentially connected along a horizontal optical path, and the first flat beam splitter and the first zero-degree total reflection mirror are arranged parallel to each other, and the cavity length spacing between them is d;

[0021] Similarly, the second laser pulse sequence generating device of the present invention is composed of a second flat beam splitter and a second zero-degree total reflection mirror, wherein the second flat beam splitter and the second zero-degree total reflection mirror are sequentially connected along a vertical optical path, and the second flat beam splitter and the second zero-degree total reflection mirror are arranged parallel to each other, and the cavity length distance between them is D;

[0022] The present invention sets the cavity length spacing between the first flat beam splitter and the first zero-degree total reflection mirror in the first laser pulse sequence generating device to d, and sets the cavity length spacing between the second flat beam splitter and the second zero-degree total reflection mirror in the second laser pulse sequence generating device to D; when adjusting the cavity length spacing D and the cavity length spacing d, the sub-pulse sequence time interval can be adjusted in the range of 1ps to 1500ps. The adjustment range of the laser pulse frequency of the conventional 4f structure pulse shaping system is only 0.25ps to 16.2ps. The present invention has the advantage of a large adjustable range of the sub-pulse sequence time interval.

[0023] The first laser pulse sequence generating device of the present invention is composed of a first flat beam splitter and a first zero-degree total reflection mirror, and the second laser pulse sequence generating device is composed of a second flat beam splitter and a second zero-degree total reflection mirror. The arrangement of the first zero-degree total reflection mirror and the second zero-degree total reflection mirror of the present invention greatly improves the total reflectivity of the reflection and transmission of the laser pulse sequence. Since the output energy efficiency of the ultrafast laser pulse sequence is determined by the total reflectivity of the laser pulse sequence generating device, the energy efficiency of the present invention is improved. It is measured that the energy efficiency of the present invention can be greater than 90%.

[0024] In the field of femtosecond laser processing technology, improving processing efficiency requires increasing the laser repetition frequency and laser pulse energy. While the energy efficiency of the present invention reaches 90%, the adjustable range of the sub-pulse interval is expanded to 1500 ps compared to the traditional 4f structure pulse shaping system, and the attenuation rate of the fifth sub-pulse relative to the maximum sub-pulse in a single pulse sequence is reduced from 95% to 41%, which greatly increases the number of effective sub-pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the present invention. DETAILED DESCRIPTION

[0026] See also Figure 1 , the present invention comprises a half wave plate 1, an optical path deflection device 100, a first laser pulse sequence generating device 200 and a second laser pulse sequence generating device 300;

[0027] The optical path deflection device 100 is composed of a polarization beam splitter cube 2, a first quarter wave plate 3 and a second quarter wave plate 6; the polarization beam splitter cube 2 and the first quarter wave plate 3 are sequentially connected along a horizontal optical path, and the polarization beam splitter cube 2 and the second quarter wave plate 6 are sequentially connected along a vertical optical path;

[0028] The first laser pulse sequence generating device 200 is composed of a first flat beam splitter 4 and a first zero-degree total reflector 5; the first flat beam splitter 4 and the first zero-degree total reflector 5 are sequentially connected along a horizontal optical path;

[0029] The second laser pulse sequence generating device 300 is composed of a second flat beam splitter 7 and a second zero-degree total reflection mirror 8; the second flat beam splitter 7 and the second zero-degree total reflection mirror 8 are sequentially connected along a vertical optical path;

[0030] The half-wave plate 1, the optical path deflection device 100 and the first laser pulse sequence generating device 200 are sequentially arranged in the horizontal direction, wherein the half-wave plate (1) and the optical path deflection device The polarization beam splitter cube 2 and the first quarter wave plate 3 of the optical path deflection device 100 are sequentially connected with the first flat beam splitter 4 of the first laser pulse sequence generating device 200 along the horizontal optical path;

[0031] The optical path deflecting device 100 and the second laser pulse sequence generating device 300 are sequentially arranged along the vertical direction, wherein the second quarter wave plate 6 of the optical path deflecting device 100 and the second flat beam splitter 7 of the second laser pulse sequence generating device 300 are sequentially connected along the vertical optical path.

[0032] The present invention sets up the process as follows:

[0033] 1) See Figure 1 The half wave plate 1, the optical path deflection device 100, the first laser pulse sequence generating device 200 and the second laser pulse sequence generating device 300 are respectively installed on the optical frame.

[0034] 2) See Figure 1 , the input ultrafast laser pulse is incident on the half wave plate 1 and the polarization beam splitter cube 2 in sequence, and the half wave plate 1 is rotated so that the laser power after the polarization beam splitter cube 2 is maximized. At this time, the polarization of the ultrafast laser has been adjusted from the half wave plate to p-polarized light.

[0035] 3) See Figure 1 A first quarter wave plate 3 is arranged behind the polarization beam splitter cube 2, so that the laser is incident on the first quarter wave plate 3, and the first quarter wave plate 3 is rotated so that its fast axis and the p-polarization direction are 45 degrees.

[0036] 4) See Figure 1 A first flat beam splitter 4 is arranged behind the first quarter wave plate 3, so that the laser is incident on the first flat beam splitter 4, and the reflected light of the first flat beam splitter 4 is reflected by the polarization beam splitter cube 2 via the first quarter wave plate 3, forming a 90° angle with the input light direction.

[0037] 5) See Figure 1 , fix the first zero-degree total reflection mirror 5 on the electric translation stage, and set it behind the first flat beam splitter 4, so that the laser is incident on the first zero-degree total reflection mirror 5, and the reflected light of the first zero-degree total reflection mirror 5 is split by the first flat beam splitter 4, and its transmitted light is reflected by the polarization beam splitter cube 2 through the first quarter-wave plate 3, forming an angle of 90° with the input light direction; the first zero-degree total reflection mirror 5 is oriented so that the light spots reflected from the polarization beam splitter cube 2) are co-pointed, and the installation of the first laser pulse sequence generating device 200 is completed.

[0038] 6) See Figure 1The distance between the first flat beam splitter 4 and the first zero-degree total reflection mirror 5 is adjusted by using an electric translation stage, thereby adjusting the delay time between two adjacent sub-pulses in the pulse sequence.

[0039] 7) See Figure 1 A second quarter wave plate 6 is arranged on the other side of the polarization beam splitter cube 2, so that the laser is incident on the second quarter wave plate 6, and the second quarter wave plate 6 is rotated so that its fast axis and the s polarization direction form an angle of 45°. The installation of the optical path deflection device 100 is completed.

[0040] 8) See Figure 1 A second flat beam splitter 7 is arranged behind the second quarter wave plate 6 , so that the laser is incident on the second flat beam splitter 7 , and the reflected light of the second flat beam splitter 7 is transmitted from the polarization beam splitter cube 2 via the second quarter wave plate 6 .

[0041] 9) See Figure 1 , fix the second zero-degree total reflection mirror 8 on the electric translation stage, and place it behind the second flat beam splitter 7, so that the laser is incident on the second zero-degree total reflection mirror 8; the reflected light of the second zero-degree total reflection mirror 8 is split by the second flat beam splitter 7, and its transmitted light is transmitted from the polarization beam splitter cube 2 through the second quarter-wave plate 6. Adjust the direction of the second zero-degree total reflection mirror 8 so that the light spots transmitted from the polarization beam splitter cube 2 are co-pointed, and the installation of the second laser pulse sequence generating device 300 is completed.

[0042] 10) See Figure 1 The electric translation stage is used to adjust the distance between the second flat beam splitter 7 and the second zero-degree total reflection mirror 8, thereby adjusting the delay time between two adjacent sub-pulses in the pulse sequence. Example

[0043] See also Figure 1 In this embodiment, the PHAROS femtosecond laser of Light Conversion Company is used, and the center wavelength of the emitted pulse is 1030 nm, the pulse width is 169 fs, the repetition frequency is set to 1 kHz, and the single pulse energy is 1 mJ of linearly polarized femtosecond laser;

[0044] In this embodiment, the transmission and reflection ratio of the first flat beam splitter 4 is selected as 4:6; the transmission and reflection ratio of the second flat beam splitter 7 is 4:6;

[0045] In this embodiment, the cavity length spacing d between the first flat beam splitter 4 and the zero-degree total reflection mirror 5 of the first laser pulse train generating device 200 is 7.5 mm; the cavity length spacing D between the second flat beam splitter 7 and the second zero-degree total reflection mirror 8 of the second laser pulse train generating device 300 is 15 mm; D is set to twice d, that is, D=2*d.

[0046] See also Figure 1 When working, a single linearly polarized femtosecond laser is adjusted to p-polarized light through a half-wave plate 1 in the horizontal direction, enters the optical path deflection device 100, is transmitted through a polarization beam splitter cube 2 to a first quarter-wave plate 3 at an angle of 45° between the fast axis and the p-polarized light direction, and is adjusted to circularly polarized light, and then enters the first laser pulse sequence generating device 200, passes through a first flat beam splitter 4 with a transmission and reflection ratio of 4:6, and is reflected and transmitted multiple times between the first flat beam splitter 4 and the first zero-degree total reflection mirror 5, generating a first pulse sequence with a sub-pulse time interval of 50 ps;

[0047] The first pulse sequence is incident on the optical path deflection device 100, adjusted to s-polarized light by the first quarter-wave plate 3, reflected by the polarization beam splitter cube 2 to the second quarter-wave plate 6 at a fast axis of 45° to the s-polarized light direction, adjusted to circularly polarized light, and enters the second laser pulse sequence generating device 300 for pulse sequence re-modulation, and passes through the second flat beam splitter 7 with a transmission and reflection ratio of 4:6. Each sub-pulse in the first pulse sequence is reflected and transmitted multiple times between the second flat beam splitter 7 and the second zero-degree total reflection mirror 8, and finally output from the second flat beam splitter 7. At this time, each sub-pulse is independently modulated into a cluster of sub-pulse sequences with a time interval of 100 ps. Therefore, the first pulse sequence is modulated into a multi-cluster sub-pulse sequence. The time interval between adjacent clusters in timing is 50 ps, ​​and the sub-pulse interval within the cluster is 100 ps, ​​and finally a second pulse sequence is formed. Since the time interval between adjacent clusters is 50 ps, ​​the sub-pulse interval of the second pulse sequence is 50 ps.

[0048] The second pulse sequence is finally adjusted to p-polarized light by the second quarter-wave plate 6 and is transmitted and output in the vertical direction through the polarization beam splitter cube 2.

[0049] See also Figure 1 When the cavity length spacing D between the second laser pulse sequence generating device 300 and the first laser pulse sequence generating device 200 is 2*d, the transmission and reflection ratios of the first flat beam splitter 4 and the second flat beam splitter 7 are both selected as 4:6; the energy of the obtained femtosecond laser pulse sequence is 160 μJ, 144 μJ, 201.6 μJ, 152.6 μJ, 118.7 μJ, ... ... from the first sub-pulse onwards; at least 5 sub-pulses have energies greater than 100.8 μJ.

[0050] See also Figure 1In the second pulse sequence generated by this embodiment, the attenuation rate of the fifth sub-pulse in the sub-pulse sequence is only 41.1% compared with the first sub-pulse; while in the traditional Fabry-Perot cavity transmitted light pulse sequence generation device, the attenuation rate of the second sub-pulse compared with the sub-pulse with the maximum energy is 64%, and the attenuation rate of the fifth sub-pulse compared with the sub-pulse with the maximum energy is even 95.3%. The present invention has the advantages of high energy output efficiency and a large number of effective pulses.

[0051] See also Figure 1 The pulse sequence remodulation of this embodiment is achieved as follows: the circularly polarized light adjusted by the optical path deflecting device 100 enters the first laser pulse sequence generating device 200 to generate a first pulse sequence with a pulse interval of Δt, and then passes through the optical path deflecting device 100 and enters the second laser pulse sequence generating device 300 to remodulate each sub-pulse in the sequence. The first pulse sequence is thus modulated into a multi-cluster sub-pulse sequence, and each sub-pulse is modulated into a laser sub-pulse sequence with an interval of 2*Δt. Since the sub-pulse interval within a cluster is exactly twice the time interval between clusters, the sub-pulses between different clusters overlap in timing (such as the second sub-pulse in the first cluster overlaps with the first sub-pulse in the third cluster, and so on), and finally a second pulse sequence is formed.

[0052] The above is only a further explanation of the present invention and is not intended to limit the patent of the present invention. Any equivalent implementation of the present invention should be included in the scope of the claims of the patent of the present invention.

Claims

1. A device for generating ultrafast laser pulse trains based on a Fabry-Perot cavity, characterized in that: It comprises a half-wave plate (1), an optical path deflection device (100), a first laser pulse sequence generating device (200) and a second laser pulse sequence generating device (300); The optical path deflection device (100) is composed of a polarization beam splitting cube (2), a first quarter wave plate (3) and a second quarter wave plate (6); the polarization beam splitting cube (2) and the first quarter wave plate (3) are sequentially connected along a horizontal optical path, and the polarization beam splitting cube (2) and the second quarter wave plate (6) are sequentially connected along a vertical optical path; The first laser pulse sequence generating device (200) is composed of a first flat beam splitter (4) and a first zero-degree total reflection mirror (5); the first flat beam splitter (4) and the first zero-degree total reflection mirror (5) are sequentially connected along a horizontal optical path; The second laser pulse sequence generating device (300) is composed of a second flat beam splitter (7) and a second zero-degree total reflection mirror (8); the second flat beam splitter (7) and the second zero-degree total reflection mirror (8) are sequentially connected along a vertical optical path; The half-wave plate (1), the optical path deflection device (100) and the first laser pulse sequence generating device (200) are sequentially arranged along a horizontal direction, wherein the half-wave plate (1) and the polarization beam splitting cube (2) of the optical path deflection device (100) and the first quarter-wave plate (3) of the optical path deflection device (100) and the first flat beam splitter (4) of the first laser pulse sequence generating device (200) are sequentially connected along a horizontal optical path; The optical path deflection device (100) and the second laser pulse sequence generating device (300) are sequentially arranged along a vertical direction, wherein the second quarter wave plate (6) of the optical path deflection device (100) and the second flat beam splitter (7) of the second laser pulse sequence generating device (300) are sequentially connected along a vertical optical path.

2. The device for generating ultrafast laser pulse train based on Fabry-Perot cavity according to claim 1, characterized in that: The transmission and reflection ratios of the first flat beam splitter (4) are: 1:9, 2:8, 3:7, 4:6 or 5:

5.

3. The device for generating ultrafast laser pulse train based on Fabry-Perot cavity according to claim 1, characterized in that: The transmission and reflection ratios of the second flat beam splitter (7) are 1:9, 2:8, 3:7, 4:6 or 5:

5.

4. The device for generating ultrafast laser pulse train based on Fabry-Perot cavity according to claim 1, characterized in that: The distance d between the first flat beam splitter (4) and the first zero-degree total reflection mirror (5) of the first laser pulse sequence generating device (200) is adjustable, and the adjustable range is: 0.15 to 225 mm.

5. The device for generating ultrafast laser pulse train based on Fabry-Perot cavity according to claim 1, characterized in that: The distance D between the second flat beam splitter (7) and the second zero-degree total reflection mirror (8) of the second laser pulse sequence generating device (300) is adjustable, and the adjustable range is: 0.15 to 450 mm.

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