A transmission grating compressor

Abstract

The application relates to the field of ultrafast laser technology and discloses a transmission grating compressor, which comprises a transmission diffraction grating, a lifting mirror, a right-angle turning mirror, a zero-degree reflecting mirror, a rotator and a polarization beam splitter; the polarization beam splitter is used for receiving horizontally polarized amplified pulse light and outputting; the rotator is arranged on the light output path of the polarization beam splitter and is used for rotating the polarization direction of the light beam passing through the polarization beam splitter by 45 degrees; a 1 / 2 wave plate is arranged on the light output path of the rotator, the 1 / 2 wave plate is used for adjusting the light beam into vertically polarized light and making the vertically polarized light incident on the transmission diffraction grating; the right-angle turning mirror is arranged on the light output path of the transmission diffraction grating, the right-angle turning mirror is used for reflecting the light beam diffracted by the transmission diffraction grating back to the transmission diffraction grating for re-diffraction; the lifting mirror is arranged on the light beam path reflected by the right-angle turning mirror and is used for lifting the light height of the re-diffraction light beam.

Description

Technical Field

[0001] This application relates to the field of ultrafast laser technology, and more particularly to a transmission grating compressor. Background Technology

[0002] Femtosecond lasers are widely used in semiconductor manufacturing, micro-nano fabrication, and other fields due to their ultrashort pulse widths and high peak power. Among their pulse compression techniques, the mainstream approaches include reflective grating pairs, transmissive grating pairs, and volume grating compression. Reflective and transmissive grating pair approaches require four passes through the grating, resulting in long optical paths, large space requirements (e.g., for pulses hundreds of picoseconds, the optical path needs to be lengthened), and complex adjustment. While volume grating approaches are compact, they are costly, have limited dispersion compensation capabilities, and are susceptible to thermal effects at high power. Utility Model Content

[0003] This application provides a transmission grating compressor, aiming to solve the problem in the prior art where transmission grating pairs achieve pulse compression through two grating pairs (a total of four diffractions). The core limitation is that the optical path depends on the grating pair spacing, leading to a significant increase in space occupancy as the pulse broadening increases. Although bulk gratings attempt to simplify the structure with a single device, their fabrication difficulties and dispersion limitations cannot meet the requirements for high-power, wide-broadened pulses. Currently, no technical solution has been found that combines a single transmission grating with specific optical elements (such as rotators, polarization beam splitters, right-angle conversion mirrors, lifting mirrors, and zero-degree mirrors) to achieve beam polarization state control and eight diffractions with a single grating, thereby significantly shortening the optical path and reducing space requirements without increasing the number of gratings.

[0004] In a first aspect, embodiments of this application provide a transmission grating compressor, including a transmission diffraction grating, a lifting mirror, a right-angle conversion mirror, a zero-degree reflecting mirror, a beam rotator, and a polarization beam splitter; the polarization beam splitter is used to receive and output horizontally polarized amplified pulsed light; the beam rotator is disposed on the output path of the polarization beam splitter and is used to rotate the polarization direction of the beam passing through the polarization beam splitter by 45°; a half-wave plate is disposed on the output path of the beam rotator, and the half-wave plate is used to adjust the beam into vertically polarized light and incident on the transmission diffraction grating; the right-angle conversion mirror is disposed on the output path of the transmission diffraction grating, and the right-angle conversion mirror is used to reflect the beam diffracted by the transmission diffraction grating back to the transmission diffraction grating for re-diffraction; the lifting mirror is disposed on the beam path after reflection by the right-angle conversion mirror and is used to raise the light height of the re-diffracted beam.

[0005] In some embodiments, a zero-degree reflector is provided on the light output path of the lifting mirror. The zero-degree reflector is used to reflect the light beam along the original path, so that the reflected light beam passes through the lifting mirror, the transmission diffraction grating, the right-angle turning mirror and the transmission diffraction grating in sequence for four diffractions.

[0006] In some embodiments, the light beam, after being reflected by the zero-degree mirror and undergoing four diffractions, passes through the transmission diffraction grating, the right-angle turning mirror, the transmission diffraction grating, and the lifting mirror in sequence for four more diffractions before being incident on the half-wave plate and the optical rotator.

[0007] In some embodiments, the rotator rotates the polarization direction of the beam by 45° again in the same direction, making the beam vertically polarized, and then reflects it out through the polarization beam splitter.

[0008] In some embodiments, the polarization beam splitter and the optical rotator are connected by a fixed bracket, and the incident surface of the polarization beam splitter and the incident surface of the optical rotator are kept parallel to each other to ensure that the horizontally polarized beam is incident perpendicularly onto the working plane of the optical rotator.

[0009] In some embodiments, the rotator is an electrically controlled polarization rotation device, whose rotation angle control module is electrically connected to an external control system. It is used to precisely control the two rotation operations to rotate 45° clockwise or counterclockwise according to the output polarization state of the polarization beam splitter, so as to ensure the consistency of the beam polarization state conversion.

[0010] In some embodiments, the lifting mirror is an inclined plane mirror, and its surface forms a preset angle with the path of the light beam reflected by the right-angle turning mirror. The preset angle is adjusted according to the height position of the transmissive diffraction grating and the installation height of the zero-degree mirror to precisely control the amount of light beam height increase.

[0011] In some embodiments, the reflective surface of the zero-degree mirror is coated with a total reflection film, and the center position of the zero-degree mirror is aligned with the center position of the emitted beam of the lifting mirror, so as to ensure that the reflected beam passes through the lifting mirror without deviation when it is transmitted in the reverse direction along the original optical path.

[0012] In some embodiments, the optical axis of the half-wave plate is orthogonal to the rotation axis of the optical rotator, and the central axis of the half-wave plate coincides with the central axis of the emitted beam of the optical rotator, so as to ensure that the beam after being rotated 45° is strictly converted into a vertical polarization state after passing through the half-wave plate.

[0013] In some embodiments, the right-angle turning mirror includes a first reflective surface and a second reflective surface arranged perpendicularly to each other. The first reflective surface forms a 45° angle with the direction of the emitted beam of the transmission diffraction grating, and the second reflective surface is used to reflect the diffracted beam back to the transmission diffraction grating along the original path to achieve 180° diffraction of the beam.

[0014] This invention achieves eight-fold diffraction using a single transmission grating, replacing the traditional four-fold diffraction grating scheme. This shortens the optical path by approximately 50%, significantly reducing the space occupied by the compressed optical path and facilitating miniaturized integration of the device. It supports wide beamwidths (such as nanosecond-level pulses), allowing for the use of smaller gratings with the same beamwidth, thus reducing grating costs. It avoids the high manufacturing complexity and thermal effects associated with bulk gratings, making it suitable for high-power femtosecond laser systems. By combining a rotator with a half-wave plate, it ensures the grating is always incident with optimal polarization (vertical polarization), maximizing diffraction efficiency and reducing energy loss. The optical path is folded using a right-angle concentric mirror, a lifting mirror, and a zero-degree mirror, reducing the number of optical components and adjustment complexity, and improving system stability.

[0015] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit the scope of this application. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a transmission grating compressor provided in one embodiment of this application.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0021] It should be understood that, in order to clearly describe the technical solutions of the embodiments of this utility model, the terms "first" and "second" are used in the embodiments of this utility model to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0022] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0024] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] Femtosecond lasers are widely used in semiconductor manufacturing, micro-nano fabrication, and other fields due to their ultrashort pulse widths and high peak power. Among their pulse compression techniques, the mainstream approaches include reflective grating pairs, transmissive grating pairs, and volume grating compression. Reflective and transmissive grating pair approaches require four passes through the grating, resulting in long optical paths, large space requirements (e.g., for pulses hundreds of picoseconds, the optical path needs to be lengthened), and complex adjustment. While volume grating approaches are compact, they are costly, have limited dispersion compensation capabilities, and are susceptible to thermal effects at high power.

[0026] In existing technologies, transmission gratings achieve pulse compression through two grating pairs (a total of four diffractions). Their core limitation lies in the optical path dependence on the grating pair spacing, leading to a significant increase in space occupancy as pulse broadening increases. Although volume gratings attempt to simplify the structure with a single device, their fabrication complexity and dispersion limitations cannot meet the demands for high-power, wide-broadened pulses. Currently, no technical solution has been found to combine a single transmission grating with specific optical elements (such as optical rotators, polarization beam splitters, right-angle conversion mirrors, lifting mirrors, and zero-degree mirrors) to achieve beam polarization control and eight-fold diffraction with a single grating, thereby significantly shortening the optical path and reducing space requirements without increasing the number of gratings.

[0027] Please refer to Figure 1 This application provides a transmission grating compressor, including a transmission diffraction grating, a lifting mirror, a right-angle conversion mirror, a zero-degree reflecting mirror, a beam rotator, and a polarization beam splitter. The polarization beam splitter receives and outputs amplified pulsed light with horizontal polarization. The beam rotator is disposed on the output path of the polarization beam splitter and rotates the polarization direction of the beam passing through the beam splitter by 45°. A half-wave plate is disposed on the output path of the beam rotator and is used to adjust the beam into vertically polarized light and incident it onto the transmission diffraction grating. The right-angle conversion mirror is disposed on the output path of the transmission diffraction grating and is used to reflect the beam diffracted by the transmission diffraction grating back to the transmission diffraction grating for re-diffraction. The lifting mirror is disposed on the beam path after reflection by the right-angle conversion mirror and is used to raise the beam height of the re-diffracted beam.

[0028] Specifically, addressing the problem that existing transmissive grating schemes require four diffractions, resulting in long optical paths and insufficient dispersion compensation capabilities of bulk grating schemes, this scheme achieves eight-diffraction pulse compression by combining a single transmissive grating with polarization control elements and reflection elements. This significantly shortens the optical path and reduces the space required without increasing the number of gratings, while simultaneously meeting the dispersion compensation requirements for high power and wide pulse spread.

[0029] Dynamic polarization state control is achieved by combining an optical rotator, a polarization beam splitter (PBS), and a half-wave plate to switch the polarization state of the beam, allowing the same grating to diffract beams with different polarization states multiple times. Optical path folding design: A folded optical path is constructed using a right-angle concave mirror, a lifting mirror, and a zero-degree reflecting mirror, allowing the beam to diffract back and forth multiple times on a single grating, reducing space occupation. Multiple uses of a single grating: Dispersion compensation capability is enhanced through eight diffractions (not the traditional four), overcoming the dependence of traditional schemes on grating spacing.

[0030] The core components and functions of the transmission grating compressor include: a polarization beam splitter (PBS) that receives horizontally polarized (H-polarized) pulsed light amplified at the front end, transmits and outputs H-polarized light, and reflects vertically polarized (V-polarized) light (but in this scheme, the initial input is H-polarized, so it is directly transmitted). A rotator is placed in the output path of the PBS to rotate the polarization direction of the H-polarized light by 45° (turning it into 45° linearly polarized light). A half-wave plate converts the 45° linearly polarized light into vertically polarized (V-polarized) light so that it can be incident on the transmission diffraction grating (usually, transmission gratings have higher diffraction efficiency for V-polarized light or meet specific diffraction conditions). The transmission diffraction grating performs the first diffraction on the V-polarized light, unfolding the pulse spectrum according to the wavelength (dispersion effect).

[0031] The right-angle folding mirror reflects the diffracted beam at 90°, causing it to be incident back onto the transmission grating along the original path, thus achieving a second diffraction (spectral reconvergence, accumulating dispersion).

[0032] A lifting mirror elevates the vertical beam height (beam height) of the beam along the beam path after the second diffraction by a certain distance, preventing subsequent beam paths from overlapping with previous paths and creating space for multiple round trip diffractions. A zero-degree reflector (not explicitly described in the text, but inferred from the need for optical path folding): is used to maintain the beam incident angle at 0° (or a specific angle), ensuring that the reflected beam accurately enters the next element (such as a polarizing beam splitter or optical rotator), avoiding optical path offset caused by angular deviations.

[0033] For example, the process of achieving eight diffractions (combining polarization states and optical path folding) includes: Initial polarization modulation and the first incident grating include: Input beam: A horizontally polarized (H) pulsed light, amplified at the front end, is incident on a polarization beam splitter (PBS). The PBS transmits the H-polarized light (without changing its direction). Polarization rotation: The transmitted H-polarized light is rotated 45° by a rotator to become 45° linearly polarized light, and then converted to vertically polarized (V) light by a half-wave plate (V polarization is the diffraction polarization state required by the grating). First diffraction: The V-polarized light is incident on a transmission diffraction grating, and light of different wavelengths broadens due to different diffraction angles (dispersion expansion).

[0034] The first reflection and the second diffraction (round trip of the first group) cause the broadened beam after diffraction to be reflected by the right-angle turning mirror, reversing its direction (opposite to the direction of the incident grating), and then incident on the second grating (spectral convergence, accumulating negative dispersion). The beam after the second diffraction is shifted upward (or downward) by a certain height (e.g., Δh) by the lifting mirror to avoid the subsequent optical path from overlapping with the previous beam, preparing for the third incident.

[0035] Through polarization switching and subsequent multiple diffractions (cycled via a polarization beam splitter), the boosted beam is reflected by a zero-degree mirror and its direction is adjusted to the polarization beam splitter direction. It then passes through a half-wave plate and a rotator again to convert the V-polarized light back to H-polarized light (or by rotating the rotator 45° in the opposite direction and switching the polarization using a wave plate). When the H-polarized light is incident on the PBS, the PBS transmits the H-polarized light but reflects the V-polarized light. Therefore, the optical path needs to be designed so that the beam is incident on the PBS at a specific angle to achieve reflection (or transmission) for the next cycle. Through the above polarization switching and optical path folding, the beam height is successively raised (or lowered) by the lifting mirror each time it travels back and forth across the grating, forming a vertically misaligned folded optical path, ultimately achieving eight diffractions per grating (four round trips, each round trip involving two diffractions).

[0036] Each time the beam passes through the grating, its polarization state must satisfy the grating diffraction conditions (e.g., diffraction occurs with V-polarized incident light, but may not diffract or may diffract at a different angle with H-polarized light). By precisely switching the polarization using a rotator and waveplate, the consistent (or alternating) polarization state of the incident grating is ensured each time, thus effectively accumulating dispersion. The lifting mirror's function is to prevent light path overlap during multiple diffractions. By successively raising the beam height, a stepped path is formed in the vertical direction, compactly folded within a limited space (e.g., ...). Figure 1 The optical path shown may be zigzag-shaped or multi-layered.

[0037] Traditional four-order diffraction requires long-spaced grating pairs. This scheme uses eight-order diffraction to fold the optical path on a single grating, reducing the optical path length to only 1 / 2 to 1 / 4 of the traditional scheme (depending on the lifting mirror spacing). Eight-order diffraction provides higher-order dispersion compensation (such as second-order and third-order dispersion), suitable for wide-stretched pulses (hundreds of picoseconds). The combination of the rotator and the half-wave plate requires precise control of the polarization rotation angle (e.g., 45° ± 0.1°) to ensure consistent polarization state of the incident grating each time. The lifting height Δh is adjusted according to the pulse energy and beam diameter to avoid beam crosstalk while minimizing space occupation.

[0038] This compressor is suitable for high-power femtosecond laser systems, especially in semiconductor manufacturing (such as chip dicing) and micro / nano fabrication (such as ultra-fine drilling), solving the problems of large size and complex adjustment in traditional solutions. Future optimization directions include: integrated design: integrating the rotator, waveplate, and polarization beam splitter to reduce the number of components; thermal effect suppression: using lifting and reflecting mirrors made of low thermal expansion materials to reduce optical path drift at high power. Through the above design, a single transmission grating combined with polarization modulation and optical path folding achieves efficient and compact pulse compression, breaking through the spatial and dispersion limitations of traditional solutions.

[0039] In some embodiments, a zero-degree reflector is provided on the light output path of the lifting mirror. The zero-degree reflector is used to reflect the light beam along the original path, so that the reflected light beam passes through the lifting mirror, the transmission diffraction grating, the right-angle turning mirror and the transmission diffraction grating in sequence for four diffractions.

[0040] A closed-loop optical path is constructed using a zero-degree mirror to achieve path folding for the fourth diffraction of a single grating. A zero-degree mirror is placed at the end of the light output path of the lifting mirror, with its reflecting surface perpendicular to the beam transmission direction (incident angle 0°) to ensure that the beam is reflected back along the original path.

[0041] The beam undergoes the first diffraction through a transmission diffraction grating, followed by reflection back to the grating by a right-angle turning mirror, then a second diffraction. The beam is then raised by a lifting mirror and reflected back along the original path by a zero-degree reflecting mirror. At this point, the beam completes the first four diffractions along the path of "lifting mirror → transmission grating (third diffraction) → right-angle turning mirror → transmission grating (fourth diffraction)".

[0042] The position of the zero-degree reflector must be aligned with the center of the beam emitted from the lifting mirror to ensure that the reflected beam returns strictly along the original path and avoid optical path deviation caused by angular deviation.

[0043] In some embodiments, the light beam, after being reflected by the zero-degree mirror and undergoing four diffractions, passes through the transmission diffraction grating, the right-angle turning mirror, the transmission diffraction grating, and the lifting mirror in sequence for four more diffractions before being incident on the half-wave plate and the optical rotator.

[0044] Eight diffractions are achieved through two round trip gratings, forming a complete pulse compression optical path loop.

[0045] After completing the first four diffractions (lifting mirror → grating → concentric mirror → grating), the beam is reflected by the zero-degree mirror into the second cycle: the beam after the fourth diffraction is raised again by the lifting mirror (in the same direction as the first raising, such as upward), and then incident on the transmission grating for the fifth diffraction; after being reflected by the right-angle concentric mirror, it is incident on the grating for the sixth time, and then reflected by the lifting mirror (at this time the beam height has been cumulatively raised by 2 times Δh) → the zero-degree mirror; the seventh and eighth diffractions are completed in sequence, and finally the beam exits from the grating and returns to the 1 / 2 wave plate and the optical rotator for polarization state conversion. During the two round trips, the lifting mirror raises the beam height successively, forming a zigzag folded optical path to ensure that the eight diffractions are completed within a limited space.

[0046] In some embodiments, the rotator rotates the polarization direction of the beam by 45° again in the same direction, making the beam vertically polarized, and then reflects it out through the polarization beam splitter.

[0047] A precise conversion of the polarization state from horizontal to vertical is achieved through two unidirectional rotations of the optical rotator. The initial beam is horizontally polarized (H). After the first 45° clockwise (or counterclockwise) rotation of the optical rotator, it is converted to vertical polarization (V) by a half-wave plate. After eight diffractions, the beam passes through the optical rotator again, rotating 45° in the same direction (e.g., clockwise again). At this point, the polarization state changes from V to H+45°, and is then adjusted to H polarization by a half-wave plate. The polarization beam splitter transmits the H-polarized light, ensuring that the output beam's polarization state matches the input, thus avoiding polarization-dependent losses. The two rotations of the optical rotator must be in the same direction (both clockwise or both counterclockwise) to guarantee the deterministic nature of the polarization state conversion.

[0048] In some embodiments, the polarization beam splitter and the optical rotator are connected by a fixed bracket, and the incident surface of the polarization beam splitter and the incident surface of the optical rotator are kept parallel to each other to ensure that the horizontally polarized beam is incident perpendicularly onto the working plane of the optical rotator.

[0049] The mechanical integration design of the polarization beam splitter and the optical rotator ensures that the beam is incident perpendicularly. The polarization beam splitter (PBS) and the optical rotator are rigidly connected by a fixed bracket, and their incident surfaces are kept parallel (deviation ≤0.01°). The normal of the incident surface of the PBS coincides with the normal of the working plane of the optical rotator, ensuring that the horizontally polarized beam is transmitted through the PBS and incident perpendicularly to the optical rotator (incident angle 0°), avoiding polarization rotation errors caused by angle tilt. The bracket material is selected from aluminum alloy or titanium alloy with a low coefficient of thermal expansion to reduce the impact of temperature changes on the parallelism of the components.

[0050] In some embodiments, the rotator is an electrically controlled polarization rotation device, whose rotation angle control module is electrically connected to an external control system. It is used to precisely control the two rotation operations to rotate 45° clockwise or counterclockwise according to the output polarization state of the polarization beam splitter, so as to ensure the consistency of the beam polarization state conversion.

[0051] The electronically controlled polarization rotator achieves precise angle control, ensuring consistent polarization state conversion. The rotator employs an electronically controlled polarization rotation device (such as a magneto-optical crystal or liquid crystal rotator) with a built-in angle sensor, connecting to an external control system via RS-232 or USB interface. The control system monitors the output polarization state of the polarization beam splitter in real time (feedback signal from the reflected light detector of the PBS), dynamically adjusting the rotator's rotation angle to ensure that both rotations are strictly 45° (accuracy ±0.05°). The rotation direction (clockwise / counterclockwise) is preset by the control system, and both rotations must be in the same direction to avoid polarization state disorder caused by different directions (e.g., a first clockwise 45° rotation followed by a second counterclockwise 45° rotation would result in a net rotation of 0°).

[0052] In some embodiments, the lifting mirror is an inclined plane mirror, and its surface forms a preset angle with the path of the light beam reflected by the right-angle turning mirror. The preset angle is adjusted according to the height position of the transmissive diffraction grating and the installation height of the zero-degree mirror to precisely control the amount of light beam height increase.

[0053] The lifting mirror is tilted to precisely control the beam height increase. The lifting mirror is a plane mirror, and the beam path after reflection from the mirror and the right-angle turning mirror is at a preset angle θ (e.g., 10°~30°, adjusted according to the actual space). The beam height increase Δh = 2×L×sinθ (L is the distance from the lifting mirror to the grating). By adjusting θ, Δh can be precisely controlled to ensure that the light paths do not overlap in multiple diffractions (Δh ≥ 2× beam diameter). The calculation of the preset angle θ needs to be combined with the height position of the transmission diffraction grating and the installation height of the zero-degree mirror. The light path layout is optimized using 3D modeling software (such as Zemax) to avoid the beam hitting other components.

[0054] In some embodiments, the reflective surface of the zero-degree mirror is coated with a total reflection film, and the center position of the zero-degree mirror is aligned with the center position of the emitted beam of the lifting mirror, so as to ensure that the reflected beam passes through the lifting mirror without deviation when it is transmitted in the reverse direction along the original optical path.

[0055] The high-precision alignment and coating design of the zero-degree mirror ensures zero-offset reflection. The reflecting surface of the zero-degree mirror is coated with a total reflection film (such as a broadband film from ultraviolet to near-infrared with a reflectivity of ≥99.5%) to reduce energy loss; the center of the mirror is strictly aligned with the center of the emitted beam from the lifting mirror (deviation ≤50μm), and X / Y / Z three-dimensional calibration is achieved through a precision adjustment frame (with a micrometer); when the reflected beam travels back along the original optical path, it must pass accurately through the center of the lifting mirror, transmission grating, and other components in sequence to avoid a decrease in diffraction efficiency or optical path deviation due to offset.

[0056] In some embodiments, the optical axis of the half-wave plate is orthogonal to the rotation axis of the optical rotator, and the central axis of the half-wave plate coincides with the central axis of the emitted beam of the optical rotator, so as to ensure that the beam after being rotated 45° is strictly converted into a vertical polarization state after passing through the half-wave plate.

[0057] The half-wave plate is designed to be orthogonal to the optical axis of the rotator, ensuring strict polarization conversion. The optical axis direction (fast or slow axis) of the half-wave plate is orthogonal to the rotation axis direction of the rotator (deviation ≤1°). For example, when the rotator rotates around the beam propagation direction (Z-axis), the optical axis of the wave plate is along the X-axis. The central axis of the wave plate coincides with the central axis of the output beam of the rotator (deviation ≤100μm), ensuring that the beam after a 45° rotation passes uniformly through the wave plate and avoiding incomplete polarization conversion of the edge beam due to optical axis offset. The thickness and material (e.g., quartz) of the wave plate are customized according to the laser wavelength (e.g., 800nm) to ensure a phase delay of exactly 180° (half-wave plate condition).

[0058] In some embodiments, the right-angle turning mirror includes a first reflective surface and a second reflective surface arranged perpendicularly to each other. The first reflective surface forms a 45° angle with the direction of the emitted beam of the transmission diffraction grating, and the second reflective surface is used to reflect the diffracted beam back to the transmission diffraction grating along the original path to achieve 180° diffraction of the beam.

[0059] The right-angle deflector's dual-reflective-surface design achieves 180° aberration-free deflection. The right-angle deflector consists of two mutually perpendicular first and second reflective surfaces. The first reflective surface forms a 45° angle with the direction of the emitted beam from the transmission grating, deflecting the beam by 90°. The second reflective surface is perpendicular to the first reflective surface, receiving the first reflected beam and deflecting it again by 90°, ultimately causing the beam to reverse its path and return to the transmission grating (total deflection 180°). The perpendicularity error between the two reflective surfaces is ≤5 arcseconds. High-precision grinding and coating processes (such as metal reflective film or dielectric film) ensure reflection efficiency and avoid beam divergence or deflection caused by angular deviation.

[0060] In some embodiments, femtosecond lasers, with their extremely high peak power and narrow pulse width, have been widely used in semiconductor manufacturing, micro-nano fabrication, solar photovoltaics, and scientific research. When femtosecond lasers are used for materials processing, the extremely short duration of the light pulse interacts with the matter, injecting all its energy into a very small area of ​​interaction at an extremely high speed. The thermal effects on the material are well controlled because the extremely short duration of the light pulse allows for the rapid injection of all its energy into a small area of ​​interaction, effectively preventing heat dissipation during the material processing. However, femtosecond pulses have very high peak power, and direct amplification can easily damage devices, especially when amplified in optical fibers, where a large amount of nonlinearity accumulates. Therefore, femtosecond lasers typically employ pulse chirped amplification technology. This involves first using a stretcher to broaden the seed light pulse to the hundreds of picoseconds or even nanoseconds, and then inputting it into an amplifier for pulse amplification. The output pulse from the amplifier is then compressed by a pulse compression device, reducing the hundreds of picosecond output pulse to the femtosecond level.

[0061] Pulse compression has the following mainstream schemes: 1) Reflective grating compression scheme: This scheme typically requires two gratings. Pulse compression is achieved by adjusting the distance between the grating pairs, and it is suitable for high-energy-rate femtosecond lasers. The disadvantages of this scheme are: 1. Low grating diffraction efficiency (the laser needs to pass through the grating four times), resulting in a 30% power loss during compression; 2. Because sufficient dispersion needs to be introduced, the distance between the grating pairs will be large, thus occupying a significant amount of space and hindering miniaturization integration; 3. Complex optical path adjustment.

[0062] 2) Based on the transmission grating pair scheme, it also requires four passes through the grating. The diffraction efficiency of a single grating is >98%, and the compression efficiency is close to 90%. It is also suitable for high-power femtosecond lasers. However, this scheme also has the problem of large space occupation.

[0063] 3) Based on the volume grating compression scheme, this scheme can achieve high-quality pulse compression using only a single device. Compared to conventional grating-pair compression schemes, it occupies very little space and the optical path does not require strict collimation. Furthermore, the volume grating compression pulse efficiency can approach 95%. The problems with this scheme are that the volume grating fabrication process is difficult and costly, and the introduced dispersion and bandwidth are limited. When the pulse broadening is wide, multiple volume gratings are needed to compensate for dispersion, increasing both cost and optical path complexity. At high pulse energies, the thermal effect of the volume grating can cause beam distortion, which is unsuitable for high-power femtosecond lasers.

[0064] This invention overcomes the drawback of large space occupation of transmission grating pairs by using only one diffraction grating to achieve the function of a grating pair, while increasing the fourth diffraction of the beam to the eighth diffraction, which greatly reduces the space occupied by the compressed optical path and lowers the cost.

[0065] This invention discloses a femtosecond laser pulse width compressor, relating to the field of ultrafast lasers. The compressor includes a transmission diffraction grating, a lifting mirror, a right-angle deflection mirror, a zero-degree mirror, a rotator, and a photodiode (PBS). After four diffractions, the beam passes through the zero-degree mirror, undergoes four more diffractions, and then passes through the rotator and PBS before being output.

[0066] Typically, chirped volume gratings only offer compression of 500 ps. For higher single-pulse energies, pulse broadening to the nanosecond level is required, which chirped volume gratings cannot fully compensate for, necessitating multiple volume gratings, which is very costly. Furthermore, for high-power pulses, volume gratings are prone to thermal lensing, leading to beam quality degradation. While diffraction grating pairs are suitable for high-power lasers, compressing pulses of hundreds of picoseconds results in a very long optical path. Unlike conventional diffraction gratings with four diffraction cycles, this invention achieves eight diffraction cycles, halving the optical path length and significantly reducing the space required for compressed optical paths. Additionally, the shorter optical path greatly reduces the maximum beam spread after diffraction. Compared to traditional four-diffraction schemes, this allows for a larger broadening with the same grating size; and for the same broadening, a smaller grating size can be selected, reducing costs.

[0067] The magnified pulsed light is horizontally polarized with a center wavelength of 1030 nm, a spectral width of 8 nm, and a pulse width of approximately 800 ps. The PBS material is fused silica with an extinction ratio >1000:1. The optical rotator and half-wave plate have a center wavelength of 1030 nm. The diffraction grating has a line density of 1739.1 L / mm and a center wavelength of 1030 nm. The folding mirror and lifting mirror are both right-angled plane mirrors with a wavelength range of 1020-1070 nm. The 0° reflecting mirror has an incident angle of 0°, a wavelength range of 1020-1070 nm, and a reflectivity >99.8%.

[0068] The femtosecond amplifier beam is horizontally polarized. After passing through the PBS, it passes through a rotator, where the polarization direction is rotated by 45°. Then, it passes through a half-wave plate, which is adjusted to make the laser vertically polarized, thus maximizing the diffraction efficiency of the grating. The diffracted beam is reflected by a conversion mirror, passes through the grating again, and then diffracts again. After passing through a lifting mirror, the beam height is increased by 10 mm. Subsequently, the beam undergoes two more diffractions before reaching the 0° mirror. The reflected beam returns along the original path, undergoes four more diffractions, passes through a half-wave plate and a rotator. Compared to the initial beam incident on the rotator, the beam's polarization direction is rotated by 45° in the same direction, resulting in a vertically polarized beam that is then reflected by the PBS and output.

[0069] This invention achieves eight-fold diffraction using a single transmission grating, replacing the traditional four-fold diffraction grating scheme. This shortens the optical path by approximately 50%, significantly reducing the space occupied by the compressed optical path and facilitating miniaturized integration of the device. It supports wide beamwidths (such as nanosecond-level pulses), allowing for the use of smaller gratings with the same beamwidth, thus reducing grating costs. It avoids the high manufacturing complexity and thermal effects associated with bulk gratings, making it suitable for high-power femtosecond laser systems. By combining a rotator with a half-wave plate, it ensures the grating is always incident with optimal polarization (vertical polarization), maximizing diffraction efficiency and reducing energy loss. The optical path is folded using a right-angle concentric mirror, a lifting mirror, and a zero-degree mirror, reducing the number of optical components and adjustment complexity, and improving system stability.

[0070] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. It should be understood that when an element or layer is referred to as “on,” “adjacent to,” “connected to,” or “coupled to” other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as “directly on,” “directly adjacent to,” “directly connected to,” or “directly coupled to” other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion.

[0071] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0072] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0073] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0074] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A transmission grating compressor, characterized in that, It includes a transmission diffraction grating, a lifting mirror, a right-angle turning mirror, a zero-degree reflecting mirror, an optical rotator, and a polarizing beam splitter; The polarization beam splitter is used to receive and output horizontally polarized amplified pulsed light. The optical rotator is positioned on the output path of the polarizing beam splitter and is used to rotate the polarization direction of the beam passing through the polarizing beam splitter by 45°. A half-wave plate is provided on the light output path of the optical rotator. The half-wave plate is used to adjust the light beam into vertically polarized light and incident it onto the transmission diffraction grating. The right-angle turning mirror is provided on the light output path of the transmission diffraction grating. The right-angle turning mirror is used to reflect the light beam after diffraction by the transmission diffraction grating back to the transmission diffraction grating for diffraction again. The lifting mirror is positioned on the beam path after reflection by the right-angle turning mirror, and is used to raise the beam height after re-diffraction.

2. The transmission grating compressor according to claim 1, characterized in that, The zero-degree reflector is provided on the light output path of the lifting mirror. The zero-degree reflector is used to reflect the light beam along the original path, so that the reflected light beam passes through the lifting mirror, the transmission diffraction grating, the right-angle turning mirror and the transmission diffraction grating in sequence for four diffractions.

3. The transmission grating compressor according to claim 2, characterized in that, The beam, after being reflected by the zero-degree mirror and undergoing four diffractions, passes through the transmission diffraction grating, the right-angle turning mirror, the transmission diffraction grating, and the lifting mirror in sequence for four more diffractions before being incident on the half-wave plate and the optical rotator.

4. The transmission grating compressor according to claim 3, characterized in that, The optical rotator rotates the polarization direction of the beam by 45° in the same direction again, making the beam vertically polarized, and then reflects it out through the polarization beam splitter.

5. The transmission grating compressor according to claim 4, characterized in that, The polarization beam splitter and the optical rotator are connected by a fixed bracket, and the incident surface of the polarization beam splitter and the incident surface of the optical rotator are kept parallel to each other to ensure that the horizontally polarized beam is incident perpendicularly onto the working plane of the optical rotator.

6. The transmission grating compressor according to claim 4, characterized in that, The optical rotator is an electrically controlled polarization rotation device. Its rotation angle control module is electrically connected to an external control system. It is used to precisely control the two rotation operations to rotate 45° clockwise or counterclockwise according to the output polarization state of the polarization beam splitter, so as to ensure the consistency of the beam polarization state conversion.

7. The transmission grating compressor according to claim 2, characterized in that, The lifting mirror is an inclined plane mirror, and its surface forms a preset angle with the path of the light beam reflected by the right-angle turning mirror. The preset angle is adjusted according to the height position of the transmission diffraction grating and the installation height of the zero-degree mirror to precisely control the amount of light beam elevation.

8. The transmission grating compressor according to claim 2, characterized in that, The zero-degree reflector has a total reflection coating on its reflective surface, and the center of the zero-degree reflector is aligned with the center of the emitted beam from the lifting mirror to ensure that the reflected beam passes through the lifting mirror without deviation when it travels in the reverse direction along the original optical path.

9. The transmission grating compressor according to claim 1, characterized in that, The optical axis of the half-wave plate is orthogonal to the rotation axis of the optical rotator, and the central axis of the half-wave plate coincides with the central axis of the emitted beam of the optical rotator, so as to ensure that the beam after being rotated 45° is strictly converted into a vertical polarization state after passing through the half-wave plate.

10. The transmission grating compressor according to claim 1, characterized in that, The right-angle turning mirror includes a first reflecting surface and a second reflecting surface arranged perpendicularly to each other. The first reflecting surface forms a 45° angle with the direction of the emitted beam of the transmission diffraction grating. The second reflecting surface is used to reflect the diffracted beam back to the transmission diffraction grating along the original path to achieve 180° diffraction of the beam.

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