A method and device for adjusting the collimation of a tightly focused femtosecond laser beam

Abstract

The present invention discloses a method and device for adjusting the collimation of a tightly focused femtosecond laser beam, which are used for calibrating the collimation of a femtosecond laser. The method and device comprise a femtosecond laser, an adjustable diaphragm, an energy attenuation device, a first deflector, a second deflector, a stage, a glass slide, a microscopic vision module, and a translation stage. The femtosecond laser emits a laser beam, and the adjustable diaphragm and the energy attenuation device are coaxially arranged in sequence along the laser emission direction. The energy attenuation device is connected in series with the optical path of the microscopic vision module via the first deflector and the second deflector. The first deflector and the second deflector are connected in series along the laser optical path. The glass slide is placed on the stage surface to receive the output light of the microscopic vision module. The microscopic vision module, the second deflector, and the translation stage surface are fixedly connected.

Description

Technical Field

[0001] The present invention relates to the field of femtosecond laser technology, and in particular to a method and device for adjusting the collimation of a tightly focused femtosecond laser beam. Background Art

[0002] Tightly focused femtosecond laser beams are widely used in micro-nano manufacturing, ultrafast time-resolved imaging and detection, and micro-nanoparticle capture and transport. The collimation of tightly focused beams is an important factor in ensuring application accuracy and consistency. There are currently two methods for collimating focused femtosecond laser beams:

[0003] The first is the aperture collimation method, which first makes the unfocused light beam perpendicular to the sample stage. Then, two adjustable apertures are placed at a certain distance apart in the original laser light path. The hole centers of both apertures must be coaxial with the original light beam. Finally, a focusing objective is placed between the two apertures, and the position and angle of the lens are adjusted so that the reflected light and transmitted light spots coincide with the aperture centers behind and in front of the objective lens, respectively. The device that the laser passes through first is the last, and vice versa. This method has two shortcomings: First, the positional relationship between the center of the light spot and the center of the aperture needs to be determined by the human eye or an infrared observer. In addition, the light spots of the transmitted light and reflected light passing through the focusing objective will diverge and have weak intensity. In particular, the reflected light is very weak, making it difficult to determine the center of the light spot, resulting in low collimation accuracy. Second, the focusing objective needs to be mounted on an adjustable mechanism. When replacing the focusing objective, there is a possibility of damaging the collimation, which requires readjustment.

[0004] The other is a collimation method based on a beam profiler with a spot position recognition function. The specific method is to place a beam profiler with a beam position recognition function under the focusing objective lens, set the near point and far point between the two detectors and the focusing objective lens within a certain and appropriate range, and adjust the position and incident angle of the light beam to make the centers of the near point and far point light spots consistent on the detector. In theory, this method has high collimation accuracy, but in actual situations, placing the detector under the focused beam poses a risk of damage to the detector; in addition, it is necessary to always ensure that the detector detection surface is parallel to the surface to be processed or the plane of the system stage. In actual operation, the adjustment accuracy requirements for each device and the light beam are high, the actual operation is difficult, and it is difficult to achieve the theoretical effect.

[0005] Therefore, those skilled in the art are in urgent need of providing a technical solution that can improve the above technical problems in order to improve the current status of the existing technology. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and device for adjusting the collimation of a tightly focused femtosecond laser beam, so as to solve the problems existing in the above-mentioned prior art methods for collimating a focused femtosecond laser beam.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A collimation adjustment device for tightly focusing a femtosecond laser beam, comprising: a femtosecond laser, an adjustable aperture, an energy attenuation device, a first deflector, a second deflector, a stage, a glass slide, a microscopic vision module, and a translation stage;

[0009] The femtosecond laser emitting laser beam, the adjustable aperture, and the energy attenuation device are coaxially arranged in sequence along the laser emitting direction;

[0010] The energy attenuation device is connected in series with the optical path of the microscopic vision module through the first and second diverters;

[0011] Wherein, the first diverter and the second diverter are connected in series along the laser optical path;

[0012] The glass slide is placed on the stage surface to receive the light output by the microscopic vision module;

[0013] The microscopic vision module, the second diverter and the translation stage are fixedly connected.

[0014] Preferably, the energy attenuation device includes: a half-wave plate, a polarizer;

[0015] The half-wave plate and the polarizer are coaxially arranged in sequence along the laser emission direction.

[0016] Preferably, the microscopic vision module comprises: a focusing objective lens, a dichroic mirror, an illumination light reflector, an imaging lens, a CCD, an illumination light source and a collimating lens thereof;

[0017] The second deflector is connected to the optical path of the first dichroic mirror; the illumination light reflector and the focusing objective lens respectively receive one path of the split beam output by the first dichroic mirror; the illumination light reflector, the imaging lens, and the CCD are optically connected in series; the output light of the focusing objective lens is focused on the slide; the CCD, the imaging lens, the illumination light reflector, the first dichroic mirror, the focusing objective lens, the slide, and the stage are coaxially arranged and perpendicular to the light source emission direction of the illumination light source;

[0018] The illumination light source, the illumination light collimating lens, and the illumination light reflecting mirror are sequentially connected in series along the illumination light path.

[0019] Preferably, it further comprises a computer;

[0020] The computer is connected to the CCD signal;

[0021] The computer is connected to the stage by signal;

[0022] The computer is connected to the translation stage by signal.

[0023] Preferably, the method comprises the following steps:

[0024] Start the femtosecond laser and use an adjustable diaphragm to pre-process the position and aperture of the received laser beam so that it can output a concentric diffraction pattern;

[0025] Adjusting the power and directivity of the laser beam so that the focusing objective lens accurately receives the laser beam at the test frequency and focuses it to form a focused beam;

[0026] A glass slide placed on the stage is used to receive the focused light beam, and the microscopic vision module is used to perform microscopic imaging adjustment on the image presented on the upper surface of the glass slide to obtain a clear image;

[0027] Optimizing the power of the laser beam and reducing the laser energy of the laser beam to a level where the focused beam cannot damage the glass slide placed at the focal point;

[0028] The collimation of the tightly focused light beam is adjusted, the translation stage is moved, and the microscopic vision module is adjusted until the light intensity distribution in the diffraction pattern presented on the upper and lower surfaces of the slide is uniform and concentric with the concentric ring pattern.

[0029] Preferably, the specific steps of adjusting the power and directivity of the laser beam include:

[0030] A laser power meter is placed between the polarizer and the first deflector, the half-wave plate is rotated, the power of the laser beam is adjusted to a preset parameter, and the power meter is removed; the position and deflection angle of the first deflector and the second deflector are adjusted so that the laser beam is incident on and passes through the focusing objective lens, forming a focused beam below the focusing objective lens.

[0031] Preferably, the microscopic vision module is a microscopic imaging device using the principle of an optical microscope.

[0032] Preferably, the method for optimizing the laser beam power adopts a device that is a power attenuation device composed of the half-wave plate and the polarizer.

[0033] Preferably, the collimation adjustment of the tightly focused beam includes:

[0034] Moving the stage so that the focused light beam acts on an undamaged area of ​​the slide;

[0035] Turning off the illumination light source, setting the CCD to manual exposure mode, and setting the exposure time to obtain a clear image of the light spot, thereby obtaining an image composed of the diffraction pattern and the concentric ring pattern; wherein the concentric ring pattern is larger than the diffraction pattern;

[0036] The first deflector is adjusted to make the light intensity of the diffraction pattern uniformly distributed; and the second deflector is adjusted to make the diffraction pattern concentric with the concentric ring pattern.

[0037] Preferably, the image presented on the glass slide is observed using a display in a computer.

[0038] From the above content, it can be seen that compared with the prior art, the beneficial effects of the present invention are:

[0039] This invention has been successfully applied to femtosecond laser micro-nanofabrication, achieving significant results in improving the roundness of femtosecond laser-drilled holes, enhancing the verticality of the cut surface, and increasing the depth of the cut. Specifically, the roundness and edge quality of the microholes were enhanced. The experimental setup and process parameters used remained consistent before and after the invention. The slits were parallel to the surface perpendicular, and the sidewalls of the processed microgrooves exhibited no noticeable curvature. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0041] Figure 1 Schematic diagram of the structure of the device of the present invention;

[0042] Figure 2 (a) is a micro-hole processing quality diagram before using the present invention;

[0043] Figure 2 (b) is a quality diagram of micro-hole processing after using the present invention;

[0044] Figure 3 (a)-(b) are cross-sectional morphology comparison diagrams of the slit on the left and the micro-groove on the right processed before and after the present invention;

[0045] Figure 4 is the spot pattern before collimation;

[0046] Figure 5 is the light intensity distribution of the diffraction pattern;

[0047] Figure 6 is the spot pattern after collimation;

[0048] Figure 7 (a) The spot pattern at Z0+0.3mm after the collimation of the tightly focused beam is adjusted;

[0049] Figure 7(b) The spot pattern at Z0 after the collimation of the tightly focused beam is adjusted;

[0050] Figure 7 (c) is the spot pattern at Z0-0.3mm after the collimation of the tightly focused beam is adjusted.

[0051] In the figure: 1 femtosecond laser, 2 adjustable aperture, 3 half-wave plate, 4 polarizer, 5 deflector 1, 6 stage, 7 slide, 8 focusing objective, 9 dichroic mirror, 10 illumination light reflector, 11 illumination light source, 12 illumination light collimating lens, 13 imaging lens, 14 CCD, 15 imaging light path, 16 deflector 2, 17 translation stage, 18 laser beam, 19 computer. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0053] This embodiment 1 discloses a collimation adjustment device for a tightly focused femtosecond laser beam, comprising: a femtosecond laser 1, an adjustable aperture 2, an energy attenuation device, a first deflector 5, a second deflector 16, a stage 6, a slide 7, a microscopic vision module, and a translation stage 17. Specifically, the translation stage 17 used in this embodiment is a z-axis translation stage.

[0054] A femtosecond laser 1 emitting a laser beam, an adjustable aperture 2, and an energy attenuation device are coaxially arranged in sequence along the laser emission direction;

[0055] The energy attenuation device is connected in series with the optical path of the microscopic vision module through the diverter 1 5 and the diverter 2 16;

[0056] Among them, the diverter 1 5 and the diverter 2 16 are connected in series along the laser light path;

[0057] The slide 7 is placed on the stage 6 to receive the light output by the microscopic vision module;

[0058] The microscopic vision module is fixedly connected to the second diverter 16 and the translation stage 17.

[0059] The energy attenuation device includes: a half-wave plate 3 and a polarizer 4;

[0060] The half-wave plate 3 and the polarizer 4 are coaxially arranged in sequence along the laser emission direction.

[0061] The microscopic vision module includes: a focusing lens 8, a dichroic mirror 9, an illumination light reflector 10, an imaging lens 13, a CCD 14, an illumination light source 11 and a collimating lens 12;

[0062] The second deflector 16 is connected to the optical path of the dichroic mirror 1-9; the illumination light reflector 10 and the focusing objective lens 8 respectively receive one path of the split light output by the dichroic mirror 1-9; the illumination light reflector 10, the imaging lens 13, and the CCD 14 are connected in series in the optical path; the output light of the focusing objective lens 8 is focused on the slide 7; the CCD 14, the imaging lens 13, the illumination light reflector 10, the dichroic mirror 1-9, the focusing objective lens 8, the slide 7, and the stage 6 are coaxially arranged and perpendicular to the light emission direction of the illumination light source 11;

[0063] The illumination light source 11, the illumination light collimating lens 12, and the illumination light reflecting mirror 10 are sequentially connected in series along the illumination light path.

[0064] In addition, in this embodiment, a computer 19 is also included;

[0065] The computer 19 is connected to the CCD 14 signal;

[0066] The computer 19 is connected to the stage 6 by signal;

[0067] The computer 19 is connected to the translation stage 17 via signals. Example 2

[0068] This embodiment discloses a method for adjusting a collimation adjustment device based on a tightly focused femtosecond laser beam, comprising the following steps:

[0069] Starting the femtosecond laser and using the adjustable diaphragm 2 to pre-process the position and aperture of the received laser beam so that it can output a concentric diffraction pattern;

[0070] Adjust the power and directivity of the laser beam 18 so that the focusing lens 8 accurately receives the laser beam 18 at the test frequency and focuses it to form a focused beam;

[0071] A glass slide 7 placed on the stage 6 is used to receive the focused light beam, and the microscopic vision module is used to perform microscopic imaging adjustment on the image presented on the surface of the glass slide 7 to obtain a clear image;

[0072] Optimizing the power of the laser beam 18 and reducing the laser energy of the laser beam 18 to a level where the focused beam cannot damage the glass slide 7 placed at the focus;

[0073] The collimation of the tightly focused beam is adjusted, the translation stage 17 is moved, and the microscopic vision module is adjusted until the light intensity distribution in the diffraction pattern presented on the upper and lower surfaces of the slide 7 is uniform and concentric with the large concentric ring pattern.

[0074] Specifically:

[0075] The specific implementation of this embodiment is described by taking the application in a femtosecond laser micromachining system with a wavelength of 800nm, a pulse width of 100fs, a repetition frequency of 1000Hz, and a maximum average power of 1.5W as an example. The specific implementation is as follows:

[0076] Step 1. Adjust the position and aperture of the adjustable iris 2: Start the laser 1 to output the laser beam 18. Place a beam profiler with an attenuation plate between the adjustable iris 2 and the half-wave plate 3, remove the adjustable iris 2, and adjust the position of the beam profiler so that the laser beam is incident on the center of the beam profiler; install and adjust the position of the adjustable iris 2 so that the circular hole of the iris is concentric with the beam spot; change the circular hole aperture of the adjustable iris 2 until a concentric diffraction pattern is obtained on the beam profiler; remove the beam profiler. Due to the principle of circular hole diffraction, when the laser beam 18 output by the femtosecond laser 1 passes through the adjustable iris 2, the intensity distribution in its cross section is a concentric diffraction ring pattern;

[0077] Step 2: Coarsely adjust the power and directionality of the laser beam 18: Place a laser power meter between the polarizer 4 and the deflector 1 5, rotate the half-wave plate 3 to adjust the power of the laser beam 18 to about 3 mW, and remove the power meter; adjust the position and deflection angle of the deflector 1 5 and the deflector 2 16 so that the laser beam 18 is incident on and passes through the focusing objective lens 8, forming a focused beam below the focusing objective lens 8; turn off the laser 1 or place a light-blocking screen between the polarizer 4 and the deflector 1 5.

[0078] Step 3: Adjusting the Microscope Image: Place the slide 7 onto the stage 6, turn on the illumination source 11, and set the CCD 14 to automatic exposure mode. Change the position of the Z-axis translation stage 17, specifically adjust the distance between the focusing lens 8 and the slide to the working distance of the focusing lens, until a clear image of the upper surface of the slide 7 is obtained on the computer 19 monitor via the CCD 14. Record the Z-axis translation stage 17 position Z0 at this point. In this embodiment, the focusing lens 8 has a magnification of 20x, a numerical aperture (NA) of 0.40, and a working distance of 13 mm, and the CCD 14 is a 5-megapixel color digital camera. The stage 6 used in this embodiment is a two-dimensional stage. In actual applications, the parameters of the color digital camera, focusing lens, and stage can be modified as needed.

[0079] Step 4: Optimize the power of the laser beam 18: Restart the laser 1 or remove the light shield between the polarizer 4 and the deflector 5. At this time, the focused beam falls on the upper surface of the slide 7. The state of the laser action area can be observed through the microscopic vision module. If the slide 7 is damaged, it is necessary to further rotate the half-wave plate 3 to reduce the laser power until the focused beam does not damage the slide 7.

[0080] Step 5: Adjust the collimation of the tightly focused beam: Move the stage 6 so that the focused beam acts on the undamaged area of ​​the slide 7; turn off the illumination source 11, set the CCD 14 to manual exposure mode, and set the exposure time to between 500ms and 800ms. The specific exposure time is based on the actual image of the clear light spot. At this time, the microscopic vision module can observe something similar to Figure 4 The image shown is composed of a diffraction pattern and a concentric ring pattern, and the concentric ring pattern is larger than the diffraction pattern; Figure 5 As shown, adjust the deflector 1 5 to make the light intensity distribution of the small diffraction pattern uniform; adjust the deflector 2 16 to make the diffraction pattern concentric with the concentric ring pattern; repeat the adjustment of the deflector 1 5 and the deflector 2 16 in sequence until the light intensity distribution in the diffraction pattern is uniform and concentric with the concentric ring pattern, as shown. Figure 6 shown.

[0081] Step 6. Check the collimation of the tightly focused beam: Draw two orthogonal straight lines on the imaging interface of the microscopic vision module of the computer 19, and their intersection coincides with the center of the light spot; move the Z-axis translation stage to Z0+0.3mm and Z0-0.3mm respectively. If the light spot centers at these two locations do not deviate from the intersection of the orthogonal straight lines, Figure 7 If the collimation of the tightly focused beam is successfully adjusted, repeat steps 5 and 6.

[0082] It should be noted that the technical solution disclosed in the present invention is an obvious improvement over the existing technical solution. Figure 2 The figure shows the quality comparison of micro-holes processed on a polymer material by femtosecond laser before and after using the technical solution of the present invention. Figure 2 It can be seen that after using the technical solution of the present invention, the roundness and edge quality of the microholes are improved. Figure 3 Shown are photos of the cross-sectional morphology of slits and microgrooves processed on metal using a focused femtosecond laser before and after the use of the technical solution of the present invention. The slits in the figure are obtained by multiple scanning processes, the laser beam position is fixed, and it irradiates the sample surface from top to bottom, and the sample moves back and forth in a direction perpendicular to the paper surface. The microgrooves in the figure are obtained after completing a slit process, the sample moves 3μm to the left, and this process is repeated 10 times. Before and after the use of the technical solution of the present invention, the experimental equipment and process parameters used are kept consistent. Before the use of the present invention, as shown in FIG. Figure 3 As shown in (a), there is a certain angle between the slit and the vertical line of the surface, and the side wall of the processed micro groove appears curved. Figure 3 As shown in (b), the slit is parallel to the vertical line of the surface, and the sidewall of the processed microgroove does not show obvious bending.

[0083] For the device disclosed in the embodiment, since it corresponds to the content disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description.

[0084] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A collimation adjustment device for a tightly focused femtosecond laser beam, characterized in that: include: Femtosecond laser (1), adjustable aperture (2), energy attenuation device, diverter 1 (5), diverter 2 (16), stage (6), slide (7), microscopic vision module, translation stage (17); The femtosecond laser (1) emits a laser beam, the adjustable aperture (2), and the energy attenuation device are coaxially arranged in sequence along the laser emission direction; The energy attenuation device is connected in series with the optical path of the microscopic vision module through the first diverter (5) and the second diverter (16); Wherein, the first diverter (5) and the second diverter (16) are sequentially connected in series along the laser light path; The glass slide (7) is placed on the surface of the stage (6) to receive the light output by the microscopic vision module; The microscopic vision module is fixedly connected to the second diverter (16) and the tabletop of the translation stage (17); The method for adjusting the collimation of a tightly focused femtosecond laser beam comprises the following steps: The femtosecond laser is started, and the position and aperture of the received laser beam are pre-processed using an adjustable aperture (2) so that it can output a concentric diffraction pattern; Adjusting the power and directivity of the laser beam (18) so that the focusing objective lens (8) accurately receives the laser beam (18) at the test frequency and focuses it to form a focused beam; A glass slide (7) placed on the surface of the stage (6) is used to receive the focused light beam, and a microscopic vision module is used to perform microscopic imaging adjustment on the image presented on the upper surface of the glass slide (7) to obtain a clear image; Optimizing the power of the laser beam (18) and reducing the laser energy of the laser beam (18) to a level where the focused beam cannot cause damage to the glass slide (7) placed at the focus; The collimation of the tightly focused light beam is adjusted, the translation stage (17) is moved, and the microscopic vision module is adjusted until the light intensity distribution in the diffraction pattern presented by the upper and lower surfaces of the slide (7) is uniform and concentric with the concentric ring pattern.

2. The collimation adjustment device for a tightly focused femtosecond laser beam according to claim 1, characterized in that: The energy attenuation device comprises: a half-wave plate (3) and a polarizer (4); The half-wave plate (3) and the polarizer (4) are coaxially arranged in sequence along the laser emission direction.

3. The collimation adjustment device for a tightly focused femtosecond laser beam according to claim 1, characterized in that: The microscopic vision module comprises: a focusing objective lens (8), a dichroic mirror (9), an illumination light reflector (10), an imaging lens (13), a CCD (14), an illumination light source (11) and a collimating lens (12); The deflector 2 (16) is connected to the optical path of the dichroic mirror 1 (9); the illumination light reflector (10) and the focusing objective lens (8) respectively receive one path of split beam light output by the dichroic mirror 1 (9); the illumination light reflector (10), the imaging lens (13), and the CCD (14) are optically connected in series; the output light of the focusing objective lens (8) is focused on the glass slide (7); the CCD (14), the imaging lens (13), the illumination light reflector (10), the dichroic mirror 1 (9), the focusing objective lens (8), the glass slide (7), and the stage (6) are coaxially arranged and perpendicular to the light source emission direction of the illumination light source (11); The illumination light source (11), the illumination light collimating lens (12), and the illumination light reflector (10) are sequentially connected in series along the illumination light path.

4. The collimation adjustment device for a tightly focused femtosecond laser beam according to claim 1, characterized in that: Also includes computers (19); The computer (19) is connected to the CCD (14) by signal; The computer (19) is connected to the stage (6) via a signal; The computer (19) is connected to the translation stage (17) by signal.

5. The calibration method of the collimation calibration device based on a tightly focused femtosecond laser beam according to claim 1, characterized in that: The specific steps of adjusting the power and directionality of the laser beam include: A laser power meter is placed between the polarizer (4) and the first deflector (5), the half-wave plate (3) is rotated, the power of the laser beam (18) is adjusted to a preset parameter, and the power meter is removed; the position and deflection angle of the first deflector (5) and the second deflector (16) are adjusted so that the laser beam (18) is incident on and passes through the focusing objective lens (8), forming a focused beam below the focusing objective lens (8).

6. The calibration method of the collimation calibration device based on a tightly focused femtosecond laser beam according to claim 1, characterized in that: The microscopic vision module is a microscopic imaging device that adopts the principle of optical microscope.

7. The calibration method of the collimation calibration device based on a tightly focused femtosecond laser beam according to claim 1, characterized in that: The method for optimizing the power of the laser beam (18) adopts a device comprising: a power attenuation device composed of the half-wave plate (3) and the polarizer (4).

8. The calibration method of the collimation calibration device based on a tightly focused femtosecond laser beam according to claim 1, characterized in that: Tightly focused beam collimation adjustments include: Moving the stage (6) so that the focused light beam acts on the undamaged area of ​​the glass slide (7); Turn off the illumination light source (11), set the CCD (14) to manual exposure mode, and set the exposure time to obtain a clear image of the light spot, thereby obtaining an image composed of the diffraction pattern and the concentric ring pattern; wherein the concentric ring pattern is larger than the diffraction pattern; The first deflector (5) is adjusted to make the light intensity of the diffraction pattern uniformly distributed; and the second deflector (16) is adjusted to make the diffraction pattern concentric with the concentric ring pattern.

9. The calibration method of the collimation calibration device based on a tightly focused femtosecond laser beam according to claim 1, characterized in that: The image on the glass slide (7) is observed using a display in a computer (19).

Images