Ultrashort pulse measurement device and method based on triple frequency modulation sampling in air

Abstract

The present invention relates to an ultrashort pulse measurement device, and more specifically to an ultrashort pulse measurement device and method based on triple frequency modulation sampling in air. The device aims to address the shortcomings of the prior art, namely, the difficulty in processing solid materials with a thickness of hundreds of nanometers, the lack of commercially available products, and the fact that solid materials on the market change the pulse width of a single-cycle pulse, significantly affecting the measurement results. The device comprises a compensation plate, a third high-reflection mirror, a fourth high-reflection mirror, a first wedge, a first high-reflection mirror, a second high-reflection mirror, a second wedge, a first focusing mirror, a lens, and a prism pair arranged in sequence along an optical path, as well as a baffle and a second focusing mirror arranged behind the prism pair. The device also provides a measurement method, which measures the triple frequency variation curve under different delays by adjusting a delay line, and obtains the phase and pulse width of a single-cycle laser after Fourier transformation.

Description

Technical Field

[0001] The present invention relates to an ultrashort pulse measuring device, in particular to an ultrashort pulse measuring device and method based on triple frequency modulation sampling in air. Background Art

[0002] Accurately characterizing the time-domain properties of ultrashort laser pulses is the first step in studying laser-matter interactions. With the advancement of laser technology, laser pulse widths have become increasingly shorter, reaching single-cycle and even sub-cycle durations. Existing ultrashort laser pulse measurement techniques typically invert the time-domain properties by measuring the nonlinear processes of the laser in solid materials. While this technique has been well-suited for measuring multi-cycle laser pulses, single-cycle pulses are limited by the phase-matching mechanism, requiring extremely thin solid materials. For example, commonly used materials like fused silica and barium borate (BBO) require thicknesses on the order of hundreds of nanometers, making fabrication extremely complex and challenging. Consequently, no commercially available products are currently available. Furthermore, solid materials exhibit significant dispersion. For example, the thinnest commercially available 30μm fused silica can stretch a single-cycle pulse (1.3fs) with a central wavelength of 400nm to nearly five cycles (6.3fs), significantly impacting the measurement of single-cycle pulses. Consequently, existing measurement devices are unable to effectively measure single-cycle laser pulses. Summary of the Invention

[0003] The purpose of the present invention is to solve the shortcomings of the prior art, namely, the difficulty in processing solid materials with a thickness of hundreds of nanometers, the lack of commercial products available for purchase, and the fact that the solid materials on the market cause the pulse width of a single-cycle pulse to change, which has a significant impact on the measurement results. The present invention provides an ultrashort pulse measurement device and method based on triple frequency modulation sampling in air.

[0004] To achieve the above objectives, the present invention provides the following technical solutions:

[0005] An ultrashort pulse measurement device based on triple frequency modulation sampling in air, which is special in the following aspects:

[0006] The device comprises a compensating plate, a third high-reflection mirror, a fourth high-reflection mirror, a first wedge, a first high-reflection mirror, a second high-reflection mirror, a second wedge, a first focusing mirror, a lens, and a prism pair arranged in sequence along the optical path, and a second focusing mirror and a spectrometer arranged in sequence behind the prism pair; the first wedge is arranged on the incident optical path of the femtosecond laser and is used to split the incident light, the reflected part of the split light being a signal pulse, and the transmitted part being a gate pulse;

[0007] The compensation plate, the third high-reflection mirror, and the fourth high-reflection mirror are sequentially arranged on the signal pulse optical path. The compensation plate is used to compensate for the dispersion of the signal pulse, and the third high-reflection mirror and the fourth high-reflection mirror are used to reflect the signal pulse. The first high-reflection mirror and the second high-reflection mirror are arranged on a translation stage to form a delay line. The delay line is arranged on the gate pulse optical path to reflect the gate pulse and adjust the delay.

[0008] The second wedge is arranged at the intersection of the signal pulse reflected by the fourth high-reflection mirror and the gate pulse reflected by the delay line. The second wedge is the same as the first wedge and is used to combine the signal pulse reflected by the second wedge and the gate pulse transmitted by the second wedge to form a combined light beam; the first focusing mirror and the lens are arranged in sequence on the combined light path, the first focusing mirror is used to focus the combined light beam into the air and generate tripled frequency light in the air, the focused light is fundamental frequency light, and the lens is used to collimate the fundamental frequency light and the tripled frequency light to form collimated light; the prism pair is arranged on the collimated light path, and is used to divide the collimated light into fundamental frequency light and tripled frequency light; the second focusing mirror is arranged on the tripled frequency light path, and is used to focus the tripled frequency light into the spectrometer for measurement.

[0009] Furthermore, the first wedge and the second wedge are both fused silica wedges with a top corner thickness of 0.2 mm and a top angle of 1-10°.

[0010] Furthermore, the reflectivity of the first high-reflection mirror, the second high-reflection mirror, the third high-reflection mirror and the fourth high-reflection mirror is greater than 99%.

[0011] Furthermore, it also includes a baffle arranged on the fundamental frequency light path, which is used to block the fundamental frequency light.

[0012] Furthermore, the first focusing mirror is a concave silver mirror with a focal length of 100 mm;

[0013] The lens and the second focusing lens are both calcium fluoride lenses, and the focal lengths are 100 mm and 50 mm respectively.

[0014] Furthermore, the prism pair includes a first prism and a second prism, both of which are calcium fluoride prisms.

[0015] Furthermore, the baffle is a light-proof baffle;

[0016] The vertex angle between the first wedge and the second wedge is 2°;

[0017] The compensation plate is set to be a fused quartz plate with a thickness of 1 mm.

[0018] At the same time, a method for measuring ultrashort pulses based on triple frequency modulation sampling in air is also provided, which uses the above-mentioned ultrashort pulse measurement device based on triple frequency modulation sampling in air. The method is special in that it includes the following steps:

[0019] S1. Using a first wedge to split incident laser light into a signal pulse and a gate pulse, the gate pulse is reflected by a delay line and then transmitted through a second wedge. The signal pulse passes through a compensating plate and is reflected by a third and fourth high-reflection mirrors to the second wedge. After reflection from the second wedge, it is proportionally combined with the gate pulse transmitted through the second wedge to form a combined light beam. The combined light beam is focused into air via a first focusing mirror to generate tripled frequency light. The focused light is fundamental frequency light. The fundamental frequency light and tripled frequency light are collimated simultaneously by a lens and then split by a prism. After splitting, the fundamental frequency light is blocked by a baffle, and the tripled frequency light is focused by a second focusing mirror into a spectrometer for intensity measurement. The incident angles of the first and second wedges are the same.

[0020] S2. Adjust the delay line, measure the intensity of the tripled frequency light at different delays, and plot a curve showing how the intensity of the tripled frequency light changes with the delay line modulation.

[0021] S3. After Fourier transforming the curve obtained in S2, the spectrum and spectral phase diagram of the laser, as well as the pulse width curve diagram, are obtained.

[0022] Furthermore, in S1, the proportional beam combining is specifically: adjusting the percentage of the energy of the signal pulse to the energy of the gate pulse by adjusting the angles of the incident light of the first wedge and the second wedge, wherein the percentage is less than 1%.

[0023] Furthermore, the spectrometer described in S1 is an ultraviolet spectrometer.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention uses a first wedge to separate laser light into a signal pulse and a gate pulse. A second wedge combines the signal pulse and the gate pulse in a certain ratio, and then focuses the combined light in air through a first focusing mirror to generate tripled frequency light. Because the refractive index of air changes very little with wavelength, the phase matching length of its tripled frequency can reach the millimeter level. In addition, the dispersion of air is three orders of magnitude less than that of solid materials, and the broadening of single-cycle pulses is negligible. After filtering and collimating the tripled frequency light through a lens, a second focusing mirror is used to focus it onto a spectrometer. By adjusting the delay line, a curve graph of the tripled frequency light as it changes with the delay line modulation is measured. Finally, this curve graph is Fourier transformed to obtain the phase and bandwidth of the single-cycle laser.

[0026] 2. In the present invention, the preferred apex thickness of the first and second wedges is 0.2 mm, and the apex angle range is 1-10°. Both surfaces of the wedge forming the apex angle are reflective, and during use, only the reflected light from the surface close to the incident light is used. However, if the apex angle is too small, it will not be conducive to the spatial beam splitting of the reflected light from the two surfaces. If the angle is too large, the wedge thickness will be too thick, introducing excessive dispersion and affecting the accuracy of pulse measurement.

[0027] 3. The triple frequency modulation sampling in air in the present invention is based on perturbation theory. In perturbation theory, a strong gate pulse is required to generate triple frequency, and then a weak signal pulse is used for perturbation. Therefore, the present invention preferably sets the ratio of the energy of the signal pulse to the energy of the gate pulse to be less than 1%. When the ratio is greater than this, the measurement error will be too large. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the optical path principle of an embodiment of an ultrashort pulse measurement device based on triple frequency modulation sampling in air according to the present invention;

[0029] Figure 2 is a graph showing how the intensity of the tripled frequency light measured in an embodiment of the present invention changes with the modulation of the delay line;

[0030] Figure 3 Yes Figure 2 The spectrum obtained after Fourier transformation of the curve shown and the curve of the spectrum phase;

[0031] Figure 4 Yes Figure 2 The pulse width curve obtained after Fourier transformation of the curve shown;

[0032] Description of reference numerals:

[0033] 1-femtosecond laser, 2-first wedge, 3-compensation plate, 4-third high-reflection mirror, 5-fourth high-reflection mirror, 6-first high-reflection mirror, 7-second high-reflection mirror, 8-translation stage, 9-second wedge, 10-first focusing mirror, 11-lens, 12-first prism, 13-second prism, 14-baffle, 15-second focusing mirror, 16-spectrometer. DETAILED DESCRIPTION

[0034] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments:

[0035] The present invention provides an ultrashort pulse measurement device based on triple frequency modulation sampling in air, such as Figure 1As shown, it includes a compensation plate 3, a third high-reflection mirror 4 and a fourth high-reflection mirror 5, a first wedge 2, a first high-reflection mirror 6, a second high-reflection mirror 7, a second wedge 9, a first focusing mirror 10, a lens 11 and a prism pair arranged in sequence along the optical path, and a second focusing mirror 15 and a spectrometer 16 arranged in sequence behind the prism pair.

[0036] A femtosecond laser 1 emits laser light. The first wedge 2 is arranged in the incident optical path of the laser and divides the incident light into a reflected part and a transmitted part, the reflected part being a signal pulse and the transmitted part being a gate pulse. The compensating plate 3, the third high-reflective mirror 4, and the fourth high-reflective mirror 5 are arranged in sequence in the optical path of the signal pulse. The compensating plate 3 is a fused quartz plate with a thickness of 1 mm and is used to compensate for the dispersion of the signal pulse introduced by the first wedge 2 and the second wedge 9. The third high-reflective mirror 4 and the fourth high-reflective mirror 5 are used to reflect the signal pulse. The first high-reflective mirror 6 and the second high-reflective mirror 7 are arranged in the optical path of the gate pulse and, together with the piezoelectric ceramic translation stage 8, form a delay line for reflecting the gate pulse and adjusting the delay. The reflectivity of the first high-reflective mirror 6, the second high-reflective mirror 7, the third high-reflective mirror 4, and the fourth high-reflective mirror 5 is greater than 99%.

[0037] The second wedge 9 is arranged at the intersection of the signal pulse reflected by the fourth high-reflection mirror 5 and the gate pulse reflected by the delay line, and is used to combine the signal pulse reflected by the second wedge 9 and the gate pulse transmitted by the second wedge 9 to form a combined light beam. The second wedge 9 is the same as the first wedge 2, and both are made of fused silica with a top thickness of 0.2 mm and a top angle of 2°. The first focusing mirror 10 and the lens 11 are sequentially arranged on the combined light path. The first focusing mirror 10 is a concave silver mirror with a focal length of 100 mm, and is used to focus the combined light beam into the air and generate tripled frequency light in the air. The focused light is the fundamental frequency light. The lens 11 It is a calcium fluoride lens with a focal length of 100mm, which is used to collimate the fundamental frequency light and the tripled frequency light to form collimated light; the prism pair is arranged in the collimated light path, which is used to separate the collimated light into the fundamental frequency light and the tripled frequency light; the prism pair includes a first prism 12 and a second prism 13, and the first prism 12 and the second prism 13 are both splitter prisms, made of calcium fluoride; the baffle 14 is an opaque baffle, which is arranged in the fundamental frequency light path, which is used to form a barrier for the fundamental frequency light; the second focusing mirror 15 is arranged in the tripled frequency light path, which is a calcium fluoride lens with a focal length of 50mm, which is used to focus the tripled frequency light into the spectrometer 16 for measurement.

[0038] In other embodiments of the present invention, compensation sheets 3 and wedges of other specifications may also be used. The value range of the wedge top angle is 1-10°. The larger the angle, the thicker the compensation sheet 3 used. The thickness of the compensation sheet is 0.5-5mm. The focal length of the first focusing mirror 10, the specifications of the lens 11 and the second focusing mirror 15 can all be selected from other specifications. The larger the focal length, the larger the size of the measuring device of the present invention.

[0039] In combination with the actual process of measuring single-cycle laser, a method for using an ultrashort pulse measurement device based on triple frequency modulation sampling in air is as follows:

[0040] S1. A femtosecond laser 1 emits laser light, and a first wedge 2 is used to split the incident laser light into a signal pulse and a gate pulse. The gate pulse is reflected by a delay line and then transmitted through a second wedge 9. The signal pulse passes through a compensation plate 3 and is reflected by a third high-reflection mirror 4 and a fourth high-reflection mirror 5 to a second wedge 9. After being reflected by the second wedge 9, the signal pulse is proportionally combined with the gate pulse transmitted through the second wedge 9 to form a combined light beam. The combined light beam is focused into the air by a first focusing mirror 10 to generate tripled frequency light. The focused light is fundamental frequency light. The fundamental frequency light and tripled frequency light are simultaneously collimated by a lens 11 and then split by a prism. After splitting, the fundamental frequency light is blocked by a baffle 14, and the tripled frequency light is focused by a second focusing mirror 15 to a spectrometer 16 for measurement of its intensity. The incident angles of the first wedge 2 and the second wedge 9 are the same.

[0041] The proportional beam combining is specifically as follows: adjusting the incident light angles of the first wedge 2 and the second wedge 9 to adjust the percentage of the energy of the signal pulse to the energy of the gate pulse. In this embodiment, the percentage is 0.8%. In other embodiments of the present invention, other values ​​of the percentage less than 1% have good effects. The spectrometer 16 in this embodiment is an ultraviolet spectrometer.

[0042] S2. Adjust the delay line, measure the intensity of the tripled frequency light under different delays, and draw a curve of the intensity of the tripled frequency light as the delay line modulation changes, such as Figure 2 As shown;

[0043] S3. After Fourier transforming the curve obtained in S2, we can obtain Figure 3 The spectrum and spectral phase diagram shown, as well as Figure 4 The pulse width diagram of the laser is shown by Figure 4 The laser pulse width can be obtained as 28fs.

Claims

1. An ultrashort pulse measurement device based on triple frequency modulation sampling in air, characterized by: The invention comprises a compensation plate (3), a third high-reflection mirror (4), and a fourth high-reflection mirror (5); a first wedge (2), a first high-reflection mirror (6), a second high-reflection mirror (7), a second wedge (9), a first focusing mirror (10), a lens (11), and a prism pair arranged in sequence along the optical path; and a second focusing mirror (15) and a spectrometer (16) arranged in sequence behind the prism pair. The first wedge (2) is arranged on the incident light path of the femtosecond laser and is used to split the incident light, wherein the reflected part after the splitting is a signal pulse and the transmitted part is a gate pulse; The compensation plate (3), the third high-reflection mirror (4) and the fourth high-reflection mirror (5) are sequentially arranged on the signal pulse optical path, the compensation plate (3) is used to compensate for the dispersion of the signal pulse, and the third high-reflection mirror (4) and the fourth high-reflection mirror (5) are used to reflect the signal pulse; The first high-reflection mirror (6) and the second high-reflection mirror (7) are arranged on a translation stage (8) to form a delay line, which is arranged on the gate pulse optical path and is used to reflect the gate pulse and adjust the delay; The second wedge (9) is arranged at the intersection of the signal pulse reflected by the fourth high-reflection mirror (5) and the gate pulse reflected by the delay line. The second wedge (9) is the same as the first wedge (2) and is used to combine the signal pulse reflected by the second wedge (9) and the gate pulse transmitted by the second wedge (9) to form a combined light beam. The first focusing mirror (10) and the lens (11) are sequentially arranged on the combined light path, the first focusing mirror (10) is used to focus the combined light into the air and generate tripled frequency light in the air, the focused light being the fundamental frequency light, and the lens (11) is used to collimate the fundamental frequency light and the tripled frequency light to form collimated light; The prism pair is arranged on the collimated light path and is used to separate the collimated light into fundamental frequency light and triple frequency light; The second focusing mirror (15) is arranged on the triple frequency light path and is used to focus the triple frequency light into the spectrometer (16) for measurement.

2. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to claim 1, characterized in that: The first wedge (2) and the second wedge (9) are both fused silica wedges with a top corner thickness of 0.2 mm and a top corner angle of 1-10°.

3. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to claim 2, characterized in that: The reflectivity of the first high-reflection mirror (6), the second high-reflection mirror (7), the third high-reflection mirror (4) and the fourth high-reflection mirror (5) is greater than 99%.

4. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to any one of claims 1 to 3, characterized in that: It also includes a baffle (14) arranged on the fundamental frequency light path, used for forming a baffle for the fundamental frequency light.

5. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to claim 4, characterized in that: The first focusing mirror (10) is a concave silver mirror with a focal length of 100 mm; The lens (11) and the second focusing lens (15) are both calcium fluoride lenses (11), and their focal lengths are 100 mm and 50 mm respectively.

6. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to claim 5, characterized in that: The prism pair comprises a first prism (12) and a second prism (13), both of which are calcium fluoride prisms.

7. The ultrashort pulse measurement device based on triple frequency modulation sampling in air according to claim 6, characterized in that: The baffle (14) is a light-proof baffle; The vertex angles of the first wedge (2) and the second wedge (9) are 2°; The compensation plate (3) is configured as a fused quartz plate with a thickness of 1 mm.

8. A method for measuring ultrashort pulses based on triple frequency modulation sampling in air, using the ultrashort pulse measurement device based on triple frequency modulation sampling in air according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Using the first wedge (2) to split the incident laser light, a signal pulse and a gate pulse are formed. The gate pulse is reflected by the delay line and then transmitted through the second wedge (9). The signal pulse is reflected by the third high-reflection mirror (4) and the fourth high-reflection mirror (5) to the second wedge (9) after passing through the compensation plate (3). After being reflected by the second wedge (9), the signal pulse is combined with the gate pulse transmitted through the second wedge (9) in proportion to form a combined light. The combined light is focused into the air by the first focusing mirror (10) to generate tripled frequency light. The focused light is the fundamental frequency light. The fundamental frequency light and the tripled frequency light are collimated by the lens (11) at the same time and then split by the prism. After the splitting, the fundamental frequency light is blocked by the baffle (14). The tripled frequency light is focused by the second focusing mirror (15) into the spectrometer (16) to measure its intensity. The incident light angles of the first wedge (2) and the second wedge (9) are the same; S2. Adjust the delay line, measure the intensity of the tripled frequency light at different delays, and plot a curve showing how the intensity of the tripled frequency light changes with the delay line modulation. S3. After Fourier transforming the curve obtained in S2, the spectrum and spectral phase diagram of the laser, as well as the pulse width curve diagram, are obtained.

9. The method for measuring ultrashort pulses based on triple frequency modulation sampling in air according to claim 8, characterized in that: In S1, the proportionate beam combining is specifically: adjusting the angles of the incident light of the first wedge (2) and the second wedge (9) to adjust the percentage of the energy of the signal pulse to the energy of the gate pulse, wherein the percentage is less than 1%.

10. The ultrashort pulse measurement method based on triple frequency modulation sampling in air according to claim 8, characterized in that: The spectrometer (16) described in S1 is an ultraviolet spectrometer.

Images