CN116642668A - Device and method for measuring damage threshold of femtosecond laser lens - Google Patents
Device and method for measuring damage threshold of femtosecond laser lens Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring a damage threshold of a femtosecond laser lens. The invention comprises a laser, a switch, an attenuator, an energy online measurement module and a sample test module, wherein the sample test module comprises a vacuum cavity, a focusing test system, damage monitoring laser and an optical garbage can, and the focusing test system comprises a focusing mirror, a second lens and first to third cameras; the invention adopts a camera, an energy meter and damage monitoring laser to measure the damage threshold value of the sample surface on line in real time; the laser parameters of each laser irradiation on the sample can be recorded, and the damage threshold of the sample can be accurately obtained; in addition, the whole device is placed in vacuum, so that the laser parameter deterioration caused by the nonlinear effect of high-peak-power laser in the atmosphere is avoided, and the test is more accurate.
Description
Technical Field
The invention relates to the field of lasers, in particular to a device and a method for measuring a damage threshold of a femtosecond laser lens.
Background
With the development of laser technology, the pursuit of higher peak power lasers has been one of the targets for laser development. Compressing the laser pulse width is an important method of boosting the laser peak pulse. As the peak power of the laser continues to rise, higher demands are placed on the damage threshold of the optical element, especially the damage of the optical element by the femtosecond laser pulses. It is therefore particularly important how to accurately measure the damage threshold of the femtosecond laser optical element.
ISO standard 21254 is currently the standard for measuring damage threshold, and this method is generally shown in fig. 1: focusing a beam of laser on a sample to be detected in the atmosphere through a focusing lens, wherein the sample to be detected is a lens, measuring laser energy, pulse width and focal spot at a focal point before placing the sample, and placing the sample on the focal point after obtaining data, wherein the laser is used for single shot or continuous multi-shot application, and taking down the sample to observe whether the lens is damaged under a microscope after the laser and the sample are acted on, and taking the light acted on the sample as a sample damage threshold when the lens is just damaged. In the prior art, the laser energy, pulse width and focal spot are measured in non-real time, and the accuracy of the final damage threshold is interfered. In addition, whether the sample is damaged or not is measured in non-real time, so that the efficiency is affected. In addition, the whole test is carried out in the atmosphere, and in the case that the femtosecond laser energy damages the lens, the intensity of the femtosecond laser energy can cause nonlinear effect in the atmosphere, which is inaccurate to the laser parameters of the laser test.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a device and a method for measuring the damage threshold of a femtosecond laser lens.
The invention aims to provide a measuring device for a damage threshold of a femtosecond laser lens.
The device for measuring the damage threshold of the femtosecond laser lens comprises: the device comprises a laser, a switch, an attenuator, an energy online measurement module and a sample test module; wherein,,
the laser emits femtosecond laser with the center wavelength lambda 0 ；
The switch is arranged on the light path between the laser and the attenuator, and controls the laser to send one or more femtosecond lasers to enter the subsequent light path according to the requirement;
the attenuator continuously attenuates the energy of the femtosecond laser, so as to adjust the energy of the femtosecond laser entering a subsequent light path;
the energy online measurement module comprises a first lens and a first energy meter; the femtosecond laser after passing through the attenuator is incident on the first lens, most of the femtosecond laser is reflected by the first lens, and the small part of the femtosecond laser is transmitted by the first lens; the femtosecond laser reflected by the first lens is used for damage threshold measurement, enters a sample testing module, and enters a first energy meter for energy measurement;
the sample testing module comprises a vacuum cavity, a focusing testing system, damage monitoring laser and an optical garbage can; the damage monitoring laser and the optical garbage can are arranged outside the vacuum cavity; first to third windows are respectively arranged on the side wall of the vacuum cavity; the focusing test system is arranged in the vacuum cavity and comprises a focusing mirror, a second lens and first to third cameras; the femtosecond laser reflected by the first lens enters the vacuum cavity through the first window, is focused by the focusing lens, and is incident on the second lens, most of the femtosecond laser is reflected by the second lens, and the small part of the femtosecond laser is transmitted by the second lens; the femtosecond laser reflected by the second lens is incident on a sample with a damage threshold to be measured, the sample is subjected to damage test, and the incident angle of the femtosecond laser incident on the sample is theta 1; the femtosecond laser transmitted by the second lens enters the first camera, the first camera is provided with a first lens, the first camera images the focus of the femtosecond laser transmitted by the second lens, and the femtosecond laser reflected by the second lens and the femtosecond laser transmitted by the second lens are both light focused by the focusing lens, so that the first camera measures the focal spot size of the laser focused by the focusing lens in real time; the sample reflects the incident femtosecond laser, the focus of the focusing mirror is positioned on the surface of the sample, and the femtosecond laser reflected by the sample exits the vacuum cavity through the third window and is received by the optical garbage can; a second camera is arranged on the light path reflected by the sample, a lens is arranged in front of the second camera, and the second camera images the surface of the sample; the second camera is movable, and moves into the optical path when imaging the surface of the sample, and moves out of the optical path when making damage threshold measurement; setting damage monitoring laser outside the vacuum cavity, wherein the damage monitoring laser enters the vacuum cavity through a second window; the damage monitoring laser is incident on the sample at a set angle, and the damage monitoring laser is incident on the sampleThe angle is theta 2, the central wavelength of the damage monitoring laser is lambda 2, the damage monitoring laser and the femtosecond laser are overlapped on the sample, and theta 1 is not equal to theta 2, lambda 0 Not equal to λ2; a filter and a third camera are sequentially arranged along the normal direction of the surface of the sample, the surface of the filter is perpendicular to the normal, the filter reflects femtosecond laser and transmits damage monitoring laser; a lens is arranged in front of the third camera, and the third camera images the laser on the surface of the sample.
The laser is a femtosecond laser, the laser pulse width is less than 100fs, and the laser energy is more than 1mJ.
The attenuator comprises a half wave plate and a polaroid, and realizes continuous attenuation of 10% -90% of laser energy.
The reflectivity of the first lens is more than 90% and less than 99%. The focal length of the focusing mirror is greater than 1m and less than 3m. The reflectivity of the second lens is more than 90% and less than 99%. The incidence angle theta 1 of the femtosecond laser to the sample satisfies 30 DEG to theta 1 to 90 deg. The incidence angle theta 2 of the damage monitoring laser on the sample is more than or equal to 15 degrees and less than or equal to 90 degrees. Center wavelength lambda of filter for femtosecond laser 0 The reflectance of the laser is more than 90%, and the wavelength transmittance of the laser for damage monitoring with the center wavelength of lambda 2 is more than 90%.
Another object of the present invention is to provide a method for measuring a damage threshold of a femtosecond laser lens.
The invention relates to a method for measuring a damage threshold of a femtosecond laser lens, which comprises the following steps:
1) Moving a second camera into the optical path, imaging the sample surface with the second camera;
2) Moving a focusing mirror, reducing or increasing the optical path from the focusing mirror to the sample, so that the diameter of a light spot in a second camera is minimum, and converting the diameter of the light spot in linear propagation through an imaging proportion and a reflection angle, wherein the diameter of the light spot measured by the second camera before the damage threshold value measurement is D1, and the surface of the sample is the focus of the femtosecond laser;
3) Imaging a position in front of the first camera by the first camera, adjusting the position of the first camera to enable the spot diameter in the first camera to be minimum, converting the spot diameter through imaging proportion, measuring the spot diameter to be D2 by the first camera, and imaging the focus of the femtosecond laser transmitted by the second lens by the first camera;
4) Comparing the diameter D1 of the second camera measuring light spot before the damage threshold value measurement with the diameter D2 of the first camera measuring light spot, and when (1-Dth) D2 is less than or equal to D1 and less than or equal to (1+Dth) D2, dth is a light spot difference threshold value; at this point, it is believed that the first camera is able to monitor the focal spot size on the sample surface in real time; recording the position of the second camera in the optical path, moving the second camera out of the optical path, and entering step 5); returning to the step 1) when the above formula is not satisfied;
5) Placing a second energy meter in front of the sample, measuring first energy E1 of the femtosecond laser, and simultaneously obtaining second energy E2 by using the first energy meter in the energy online measurement module to obtain a correction value A=E1/E2 of the energy before the sample measured by the first energy meter in the energy online measurement module;
6) Placing a pulse width measuring instrument in front of the sample, and measuring the pulse width to be t; a second energy meter and pulse width meter before removing the sample;
7) Damage threshold measurement:
gradually increasing the energy of the femtosecond laser by using an attenuator, controlling the generation time of the femtosecond laser which is transmitted to the sample by using a switch, recording the energy Ei of each generation by using a first energy meter of an energy online measurement module, and obtaining the laser energy which is transmitted to the sample by using a correction value, wherein the incident angle of the femtosecond laser to the sample is theta 1; the first camera measures the spot diameter Di of each femtosecond laser, and the incident angle theta 1 of the femtosecond laser to the sample converts the spot area of each emission on the sample into the following areaThe light intensity of each femtosecond laser on the sample is: />
Meanwhile, the damage monitoring laser is incident on the surface of the sample, the incident angle of the damage monitoring laser incident on the sample is theta 2, theta 2 is not equal to theta 1, and the wavelength of the damage monitoring laser is different from that of the test femtosecond laser, so that the interference of the femtosecond laser on the damage surface monitoring during damage monitoring is avoided; a filter is arranged in front of the third camera and only allows the damage monitoring laser to pass through;
when the sample is damaged, the damaged sample surface of the damage monitoring laser is scattered to enter a third camera, and then the third camera can detect signals; when a signal is detected in the third camera, the damage of the sample is indicated, the femtosecond laser irradiation on the sample is stopped, and the damage threshold measurement is stopped;
8) The second camera moves into the light path and returns to the position of the second camera in the step 1), the second camera is used for imaging the position of the reflected femtosecond laser on the surface of the sample, the imaging proportion and the reflection angle are used for converting the diameter of a light spot in straight line propagation, at the moment, the diameter of the measured light spot of the second camera after the damage threshold value measurement is D3, the diameter D3 of the measured light spot of the second camera after the damage threshold value measurement is compared with the diameter D1 of the measured light spot of the second camera before the damage threshold value measurement, and the diameter D1 of (1-Dth) D1 is less than or equal to D3 is less than or equal to (1+1)
Dth) D1, it is considered that the spot is not changed during the measurement, the damage measurement is effective, and the damage threshold of the sample isWhen the above formula is not satisfied, the measurement data is invalid at this time, and the procedure returns to step 1) to re-measure.
In the step 2), the imaging proportion, namely the size proportion of the object and the image, is obtained through calibration: an object of known size is placed at the object, the size of the image is obtained in the second camera, and the imaging scale is obtained by the ratio of the object size to the image size.
In the step 4), the light spot difference threshold Dth satisfies 3% or more and 8% or less.
The invention has the advantages that:
the invention adopts a camera, an energy meter and damage monitoring laser to measure the damage threshold value of the sample surface on line in real time; the laser parameters of each laser irradiation on the sample can be recorded, and the damage threshold of the sample can be accurately obtained; in addition, the whole device is placed in vacuum, so that the laser parameter deterioration caused by the nonlinear effect of high-peak-power laser in the atmosphere is avoided, and the test is more accurate.
Drawings
FIG. 1 is a schematic diagram of a conventional device for measuring a lens damage threshold;
fig. 2 is a schematic diagram of an embodiment of a device for measuring a damage threshold of a femtosecond laser lens according to the present invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in conjunction with the accompanying drawings.
As shown in fig. 2, the measurement device for the damage threshold of the femtosecond laser lens of the embodiment includes: the device comprises a laser, a switch, an attenuator, an energy online measurement module and a sample test module; wherein,,
the laser emits femtosecond laser with the center wavelength lambda 0 The laser pulse width is less than 100fs, and the laser energy is more than 1mJ;
the switch is arranged on the light path between the laser and the attenuator, and controls the laser to send one or more femtosecond lasers to enter the subsequent light path according to the requirement;
the attenuator comprises a half wave plate and a polaroid, and is used for continuously attenuating 10% -90% of the energy of the femtosecond laser, so that the energy of the femtosecond laser entering a subsequent light path is adjusted;
the energy online measurement module comprises a first lens and a first energy meter; the femtosecond laser after passing through the attenuator is incident on the first lens, and the reflectivity of the first lens is more than 90% and less than 99%; the femtosecond laser reflected by the first lens is used for damage threshold measurement, enters a sample testing module, and enters a first energy meter for energy measurement;
the sample testing module comprises a vacuum cavity, a focusing testing system, damage monitoring laser and an optical garbage can; the focusing test system is arranged in the vacuum cavity, the focal length of the focusing mirror is more than 1m and less than 3m, and the damage monitoring laser and the optical garbage can are arranged outside the vacuum cavity; first to third windows are respectively arranged on the side wall of the vacuum cavity; femtosecond laser reflected by the first lens enters the vacuum cavity through the first window and is focused by the focusing lensThe focus is incident on the second lens, most of the femtosecond laser is reflected by the second lens, and the small part of the femtosecond laser is transmitted by the second lens, wherein the reflectivity of the second lens is more than 90% and less than 99%; the femtosecond laser reflected by the second lens is incident on a sample with a damage threshold to be measured, the sample is subjected to damage test, and the incident angle of the femtosecond laser incident on the sample is theta 1; the femtosecond laser transmitted by the second lens enters the first camera, the first camera is provided with a first lens, the first camera images the focus of the femtosecond laser transmitted by the second lens, and the femtosecond laser reflected by the second lens and the femtosecond laser transmitted by the second lens are both light focused by the focusing lens, so that the first camera measures the focal spot size of the laser focused by the focusing lens in real time; the sample reflects the incident femtosecond laser, the focus of the focusing mirror is positioned on the surface of the sample, and the femtosecond laser reflected by the sample exits the vacuum cavity through the third window and is received by the optical garbage can; a second camera is arranged on the light path reflected by the sample, a lens is arranged in front of the second camera, and the second camera images the surface of the sample; the second camera can move, when imaging the surface of the sample, the second camera needs to move into the light path, when the damage threshold value is measured, the second camera needs to move out of the light path, otherwise, when the damage threshold value is measured, the light power is too high, and the second camera is damaged; setting damage monitoring laser outside the vacuum cavity, wherein the damage monitoring laser enters the vacuum cavity through a second window; the damage monitoring laser is incident on the sample at a set angle, the incident angle of the damage monitoring laser to the sample is theta 2, the central wavelength of the damage monitoring laser is lambda 2, the damage monitoring laser and the femtosecond laser are overlapped on the sample, and theta 1 is not equal to theta 2, lambda 0 Not equal to λ2; a filter and a third camera are sequentially arranged along the normal direction of the surface of the sample, the surface of the filter is perpendicular to the normal, the filter reflects femtosecond laser and transmits damage monitoring laser, and the filter transmits the central wavelength lambda of the femtosecond laser 0 The reflectivity of the laser is more than 90 percent, and the wavelength transmittance of the laser for damage monitoring with the center wavelength of lambda 2 is more than 90 percent; a lens is arranged in front of the third camera, and the third camera images the laser on the surface of the sample.
The method for measuring the damage threshold of the femtosecond laser lens in the embodiment comprises the following steps:
1) Moving a second camera into the optical path, imaging the sample surface with the second camera;
2) Moving a focusing mirror, reducing or increasing the optical path from the focusing mirror to the sample, so that the diameter of a light spot in a second camera is minimum, and converting the diameter of the light spot in linear propagation through an imaging proportion and a reflection angle, wherein the diameter of the light spot measured by the second camera before the damage threshold value measurement is D1, and the surface of the sample is the focus of the femtosecond laser;
3) Imaging the position 2-3 cm in front of the first camera by the first camera, adjusting the position of the first camera to enable the spot diameter in the first camera to be minimum, converting the spot diameter through imaging proportion, measuring the spot diameter to be D2 by the first camera, and imaging the focus of the femtosecond laser transmitted by the second lens by the first camera;
4) Comparing the diameter D1 of the second camera measuring light spot before the damage threshold measurement with the diameter D2 of the first camera measuring light spot, and when (1-5%) D2 is less than or equal to D1 and less than or equal to (1+5%) D2, at the moment, considering that the first camera can monitor the size of the focal spot on the surface of the sample in real time; recording the position of the second camera in the optical path, moving the second camera out of the optical path, and entering step 5;
returning to the step 1) when the above formula is not satisfied;
5) Placing a second energy meter in front of the sample, measuring first energy E1 of the femtosecond laser, and simultaneously obtaining second energy E2 by using the first energy meter in the energy online measurement module to obtain a correction value A=E1/E2 of the energy before the sample measured by the first energy meter in the energy online measurement module;
6) Placing a pulse width measuring instrument in front of the sample to measure the pulse width as t; a second energy meter and pulse width meter before removing the sample;
7) Damage threshold measurement:
gradually increasing the energy of the femtosecond laser by using an attenuator, controlling the generation time of the femtosecond laser which is transmitted to the sample by using a switch, recording the energy Ei of each generation by using a first energy meter of an energy online measurement module, and obtaining the laser energy which is transmitted to the sample by using a correction value, wherein the incident angle of the femtosecond laser to the sample is theta 1; first cameraMeasuring the spot diameter Di of each femtosecond laser, and converting the spot area of each shot on the sample into the incident angle theta 1 of the femtosecond laser to the sampleThe light intensity of each femtosecond laser on the sample is: />
Meanwhile, the damage monitoring laser is incident on the surface of the sample, the incident angle of the damage monitoring laser incident on the sample is theta 2, theta 2 is not equal to theta 1, and the wavelength of the damage monitoring laser is different from that of the test femtosecond laser, so that the interference of the femtosecond laser on the damage surface monitoring during damage monitoring is avoided; a filter is arranged in front of the third camera and only allows the damage monitoring laser to pass through;
when the sample is damaged, the damaged sample surface of the damage monitoring laser is scattered to enter a third camera, and then the third camera can detect signals; when a signal is detected in the third camera, the damage of the sample is indicated, the femtosecond laser irradiation on the sample is stopped, and the damage threshold measurement is stopped;
8) The second camera moves into the light path and returns to the position of the second camera in the step 4), the second camera is used for imaging the position of the reflected femtosecond laser on the surface of the sample, the imaging proportion and the reflection angle are used for converting the diameter of a light spot in straight line propagation, the diameter of a measured light spot of the second camera after the damage threshold is D3, the diameter D3 of the measured light spot of the second camera after the damage threshold is measured is compared with the diameter D1 of the measured light spot of the second camera before the damage threshold is measured, and D1 is less than or equal to D3 (1+5%)
5%) D1, the light spot is not changed during the measurement, the damage measurement is effective, the damage threshold of the sample isWhen the above formula is not satisfied, the measurement data is invalid at this time, and the procedure returns to step 1) to re-measure.
Finally, it should be noted that the examples are disclosed for the purpose of aiding in the further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (10)
1. A measurement device for femtosecond laser lens damage threshold, characterized in that the measurement device includes: the device comprises a laser, a switch, an attenuator, an energy online measurement module and a sample test module; wherein,,
the laser emits femtosecond laser, and the center wavelength of the femtosecond laser is lambda 0;
the switch is arranged on the light path between the laser and the attenuator, and controls the laser to send one or more femtosecond lasers to enter the subsequent light path according to the requirement;
the attenuator continuously attenuates the energy of the femtosecond laser, so as to adjust the energy of the femtosecond laser entering a subsequent light path;
the energy online measurement module comprises a first lens and a first energy meter; the femtosecond laser after passing through the attenuator is incident on the first lens, most of the femtosecond laser is reflected by the first lens, and the small part of the femtosecond laser is transmitted by the first lens; the femtosecond laser reflected by the first lens is used for damage threshold measurement, enters a sample testing module, and enters a first energy meter for energy measurement;
the sample testing module comprises a vacuum cavity, a focusing testing system, damage monitoring laser and an optical garbage can; the damage monitoring laser and the optical garbage can are arranged outside the vacuum cavity; first to third windows are respectively arranged on the side wall of the vacuum cavity; the focusing test system is arranged in the vacuum cavity and comprises a focusing mirror, a second lens and first to third cameras; the femtosecond laser reflected by the first lens enters the vacuum cavity through the first window, is focused by the focusing lens, and is incident on the second lens, most of the femtosecond laser is reflected by the second lens, and the small part of the femtosecond laser is transmitted by the second lens; femtosecond laser incidence reflected by second lensThe method comprises the steps of shooting a sample with a damage threshold to be measured, entering a sample damage test, and enabling an incidence angle of femtosecond laser to enter the sample to be theta 1; the femtosecond laser transmitted by the second lens enters the first camera, the first camera is provided with a first lens, the first camera images the focus of the femtosecond laser transmitted by the second lens, and the femtosecond laser reflected by the second lens and the femtosecond laser transmitted by the second lens are both light focused by the focusing lens, so that the first camera measures the focal spot size of the laser focused by the focusing lens in real time; the sample reflects the incident femtosecond laser, the focus of the focusing mirror is positioned on the surface of the sample, and the femtosecond laser reflected by the sample exits the vacuum cavity through the third window and is received by the optical garbage can; a second camera is arranged on the light path reflected by the sample, a lens is arranged in front of the second camera, and the second camera images the surface of the sample; the second camera is movable, and moves into the optical path when imaging the surface of the sample, and moves out of the optical path when making damage threshold measurement; setting damage monitoring laser outside the vacuum cavity, wherein the damage monitoring laser enters the vacuum cavity through a second window; the damage monitoring laser is incident on the sample at a set angle, the incident angle of the damage monitoring laser to the sample is theta 2, the central wavelength of the damage monitoring laser is lambda 2, the damage monitoring laser and the femtosecond laser are overlapped on the sample, and theta 1 is not equal to theta 2, lambda 0 Not equal to λ2; a filter and a third camera are sequentially arranged along the normal direction of the surface of the sample, the surface of the filter is perpendicular to the normal, the filter reflects femtosecond laser and transmits damage monitoring laser; a lens is arranged in front of the third camera, and the third camera images the laser on the surface of the sample.
2. The measurement device of claim 1, wherein the laser is a femtosecond laser, the laser pulse width is less than 100fs, and the laser energy is greater than 1mJ.
3. The measurement device of claim 1 wherein the attenuator comprises a half wave plate and a polarizer to achieve continuous attenuation of 10% to 90% of the laser energy.
4. The measurement device of claim 1, wherein the first lens has a reflectivity of greater than 90% and less than 99%.
5. The measurement device of claim 1, wherein the focal length of the focusing mirror is greater than 1m and less than 3m.
6. The measurement device of claim 1, wherein the second lens has a reflectivity of greater than 90% and less than 99%.
7. The measurement device of claim 1, wherein an incident angle θ1 of the femtosecond laser to the sample satisfies 30 ° Σ1 Σ90 °.
8. The measurement device of claim 1, wherein the angle of incidence θ2 of the damage monitoring laser light into the sample satisfies 15 ° Σ2.
9. The measuring device of claim 1, wherein the filter has a center wavelength λ for the femtosecond laser 0 The reflectance of the laser is more than 90%, and the wavelength transmittance of the laser for damage monitoring with the center wavelength of lambda 2 is more than 90%.
10. A measurement method of the measurement device for the damage threshold of the femtosecond laser lens as set forth in claim 1, wherein the measurement method comprises the steps of:
1) Moving a second camera into the optical path, imaging the sample surface with the second camera;
2) Moving a focusing mirror, reducing or increasing the optical path from the focusing mirror to the sample, so that the diameter of a light spot in a second camera is minimum, and converting the diameter of the light spot in linear propagation through an imaging proportion and a reflection angle, wherein the diameter of the light spot measured by the second camera before the damage threshold value measurement is D1, and the surface of the sample is the focus of the femtosecond laser;
3) Imaging the position in front of the first camera by the first camera, adjusting the position of the first camera to enable the spot diameter in the first camera to be minimum, converting the spot diameter through imaging proportion, measuring the spot diameter to be D2 by the first camera, and imaging the focus of the femtosecond laser transmitted by the second lens by the first camera;
4) Comparing the diameter D1 of the second camera measuring light spot before the damage threshold value measurement with the diameter D2 of the first camera measuring light spot, and when (1-Dth) D2 is less than or equal to D1 and less than or equal to (1+Dth) D2, dth is a light spot difference threshold value; at this point, it is believed that the first camera is able to monitor the focal spot size on the sample surface in real time; recording the position of the second camera in the optical path, moving the second camera out of the optical path, and entering step 5); returning to the step 1) when the above formula is not satisfied;
5) Placing a second energy meter in front of the sample, measuring first energy E1 of the femtosecond laser, and simultaneously obtaining second energy E2 by using the first energy meter in the energy online measurement module to obtain a correction value A=E1/E2 of the energy before the sample measured by the first energy meter in the energy online measurement module;
6) Placing a pulse width measuring instrument in front of the sample, and measuring the pulse width to be t; a second energy meter and pulse width meter before removing the sample;
7) Damage threshold measurement:
gradually increasing the energy of the femtosecond laser by using an attenuator, controlling the generation time of the femtosecond laser which is transmitted to the sample by using a switch, recording the energy Ei of each generation by using a first energy meter of an energy online measurement module, and obtaining the laser energy which is transmitted to the sample by using a correction value, wherein the incident angle of the femtosecond laser to the sample is theta 1; the first camera measures the spot diameter Di of each femtosecond laser, and the incident angle theta 1 of the femtosecond laser to the sample converts the spot area of each emission on the sample into the following areaThe light intensity of each femtosecond laser on the sample is: />
Meanwhile, the damage monitoring laser is incident on the surface of the sample, the incident angle of the damage monitoring laser incident on the sample is theta 2, theta 2 is not equal to theta 1, and the wavelength of the damage monitoring laser is different from that of the test femtosecond laser, so that the interference of the femtosecond laser on the damage surface monitoring during damage monitoring is avoided; a filter is arranged in front of the third camera and only allows the damage monitoring laser to pass through; when the sample is damaged, the damaged sample surface of the damage monitoring laser is scattered to enter a third camera, and then the third camera can detect signals; when a signal is detected in the third camera, the damage of the sample is indicated, the femtosecond laser irradiation on the sample is stopped, and the damage threshold measurement is stopped;
8) The second camera moves into the light path and returns to the position of the second camera in the step 1), the second camera is used for imaging the reflected femto-second laser on the surface of the sample, the imaging proportion and the reflection angle are used for converting the diameter of a light spot in straight line propagation, the diameter of the measured light spot of the second camera after the damage threshold value measurement is D3, the diameter D3 of the measured light spot of the second camera after the damage threshold value measurement is compared with the diameter D1 of the measured light spot of the second camera before the damage threshold value measurement, (1-Dth) D1 is less than or equal to D3 and less than or equal to (1+Dth) D1, the light spot is not changed in the measurement process, the damage measurement is effective, and the damage threshold value of the sample isWhen the above formula is not satisfied, the measurement data is invalid at this time, and the procedure returns to step 1) to re-measure.
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