CN111913332A - Second harmonic bandwidth compression method - Google Patents

Second harmonic bandwidth compression method Download PDF

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Publication number
CN111913332A
CN111913332A CN202010824695.0A CN202010824695A CN111913332A CN 111913332 A CN111913332 A CN 111913332A CN 202010824695 A CN202010824695 A CN 202010824695A CN 111913332 A CN111913332 A CN 111913332A
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light
laser
crystal
frequency
harmonic
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蔡贞贞
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Jiangsu Bochuang Hanlin Photoelectric High Tech Co ltd
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Jiangsu Bochuang Hanlin Photoelectric High Tech Co ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/37—Non-linear optics for second-harmonic generation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3501—Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals

Abstract

The invention discloses a method for compressing second harmonic bandwidth, which comprises the following steps: placing the nonlinear crystal on a rotating bracket, injecting the narrow-pulse wide-bandwidth spectrum fundamental frequency light generated by a pulse laser into the nonlinear crystal, and adjusting the phase matching condition around the optical axis of the crystal according to the second harmonic
Figure DDA0002635732690000011
Axial and wave vector
Figure DDA0002635732690000012
The normal line of the formed Zk plane rotates a polar angle to realize phase matching; in a direction perpendicular to the Zk plane and passing

Description

Second harmonic bandwidth compression method
Technical Field
The invention relates to a second harmonic technology of ultrashort pulse laser, in particular to a second harmonic bandwidth compression method.
Background
In experimental research and application using ultrafast laser, it is sometimes necessary to use femtosecond pulse laser with a wide bandwidth spectrum and picosecond pulse laser with a narrow bandwidth spectrum simultaneously, for example, applications such as broadband stimulated raman scattering spectrum, broadband coherent anti-stokes raman scattering spectrum, surface and frequency vibration spectrum, and fluorescence upconversion spectrum. Aiming at converting a femtosecond laser with a wide bandwidth spectrum into a picosecond laser with a narrow bandwidth, the existing product in the market is a second harmonic bandwidth compressor of Lithowa Light Conversion company, and the product has the following defects in use: the device has a large structure and a long light path, and the stability of output light is greatly influenced by the ambient temperature; the light path adjustment and maintenance are complex, the chirp of the two beams of light needs to be ensured to have better symmetry, otherwise, the output laser has narrow pulse width and low power; the cost is high, and therefore, the related research and application are greatly limited.
Disclosure of Invention
The purpose of the invention is as follows: in view of the above problems, the present invention aims to provide a method for second harmonic bandwidth compression with short optical path and simple adjustment.
The technical scheme is as follows: the invention relates to a method for compressing second harmonic bandwidth, which comprises the following steps: placing the nonlinear crystal on a rotating bracket, injecting the narrow-pulse wide-bandwidth spectrum fundamental frequency light generated by a pulse laser into the nonlinear crystal, and adjusting the phase matching condition around the optical axis of the crystal according to the second harmonic
Figure BDA0002635732670000011
Axial and wave vector
Figure BDA0002635732670000012
The normal line of the formed Zk plane rotates a polar angle to realize phase matching; in a direction perpendicular to the Zk plane and passing
Figure BDA0002635732670000013
An in-plane rotation of the shaft changes the azimuth angle; and the polar angle and the azimuth angle are continuously optimized, and finally, the output of high-efficiency wide-pulse-width narrow-bandwidth frequency-doubled laser is realized.
Further, the fundamental frequency light is femtosecond laser output by a pulse laser.
Further, the frequency doubling laser is a femtosecond laser or a picosecond laser.
Further, the nonlinear crystal is a uniaxial crystal.
Further, the uniaxial crystal is beta-BaB2O4。
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:
1. the invention converts the femtosecond laser pulse with short pulse width and wide bandwidth into frequency doubling laser pulse with wide pulse width and narrow bandwidth in a second harmonic mode with high efficiency, short optical path, convenient adjustment and maintenance and small influence of environmental fluctuation on the optical path system;
2. the nonlinear optical coefficient is used for depending on the polar angle and the azimuth angle of the nonlinear optical crystal, phase matching is realized and a proper nonlinear optical coefficient is obtained by optimizing the polar angle and the azimuth angle, so that the optimal second harmonic conversion rate and the time domain shape of frequency doubled light are obtained.
Drawings
FIG. 1 shows polar angle θ and azimuthal angle of prior art uniaxial crystal
Figure BDA0002635732670000021
Defining a schematic diagram;
FIG. 2 is a time domain and frequency domain intensity plot of the frequency doubling simulation results of example 1;
FIG. 3 is a graph of the time domain and frequency domain intensity curves of the frequency doubling simulation results of example 2;
FIG. 4 is a graph of the time domain and frequency domain intensity curves of the frequency doubling simulation results of example 3;
FIG. 5 is a time domain and frequency domain intensity plot of the frequency doubling simulation results of example 4.
Detailed Description
The method for compressing the bandwidth of the second harmonic wave in the embodiment comprises the following steps: placing the BBO on a rotating bracket, then injecting the fundamental frequency light generated by the pulse laser into the BBO, and adjusting the phase matching condition around the optical axis of the BBO according to the second harmonic
Figure BDA0002635732670000022
Axial and wave vector
Figure BDA0002635732670000023
The normal line of the formed Zk plane rotates by a polar angle theta, and phase matching is optimized; in a direction perpendicular to the Zk plane and passing
Figure BDA0002635732670000024
In-plane rotation changing azimuth angle of shaft
Figure BDA0002635732670000025
And continuously optimize theta and
Figure BDA0002635732670000026
finally, the output of high-efficiency wide-pulse-width narrow-bandwidth frequency-doubled laser is realized.
The efficiency of the nonlinear process conversion depends on the light intensity and the effective nonlinear optical coefficient deff，deffIs formed by polar angle theta and azimuth angle
Figure BDA0002635732670000027
And (4) jointly determining. Typically, the maximum effective nonlinear coefficient is selected for use to achieve maximum conversion efficiency and other performance. However, in some applications, the non-linear coefficient is too large, which may result in a reduction in conversion efficiency and distortion of the time-domain shape of the frequency-doubled light.
FIG. 1(a) shows polar angle θ and azimuth angle of uniaxial crystal
Figure BDA0002635732670000028
The polar angle theta refers to the vector direction of the light wave
Figure BDA0002635732670000029
And crystals
Figure BDA00026357326700000210
Angle of included, azimuthal, between axes
Figure BDA00026357326700000211
Is the direction of the vector of the light wave
Figure BDA00026357326700000212
In the direction of the XY plane projection of the crystal
Figure BDA00026357326700000213
The angle between the axes. FIG. 1(b) is an angle optimization method for generating second harmonic by taking negative uniaxial crystal as an example, which realizes phase matching and optimization to obtain different nonlinear optical coefficients deffSchematic representation. Fig. 1(b) shows the incidence of horizontally polarized fundamental light, o light, i.e., ordinary light, in the crystal, frequency-doubled light, i.e., vertically polarized light, and e light, i.e., extraordinary light, in the crystal. Rotation around the normal of the ZK plane optimizes the polar angle θ to achieve phase matching. In the horizontal direction of FIG. 1(b) or perpendicular to the Zk plane and through
Figure BDA00026357326700000214
In-plane rotation of the crystal about an axis, varying azimuth
Figure BDA00026357326700000215
Changing the azimuth
Figure BDA00026357326700000216
Meanwhile, the polar angle theta is also influenced, and repeated optimization is needed
Figure BDA00026357326700000217
And θ to achieve optimization. Therefore, when the frequency doubling crystal is prepared, a proper cutting angle needs to be selected according to specific parameters of input light, and the actual use is optimized within a small and medium range
Figure BDA00026357326700000218
And theta. By varying the azimuth angle while ensuring phase matching
Figure BDA00026357326700000219
To change the nonlinear optical coefficient deff。
Example 1 laser pulses with a center wavelength of 800nm, a pulse energy of 1mJ, a pulse width of 35fs, a spectral bandwidth of 26.9nm, and a spot size of full width at half maximum of 3mm were converted into wide-pulse-width, narrow-bandwidth, doubled light pulses using BBO crystals
The calculation formula of the effective nonlinear coefficient of the second harmonic generated by the BBO crystal is as follows:
Figure BDA0002635732670000031
wherein d iseffIs the effective nonlinear optical coefficient; d31And d22Is a second order nonlinear tensor element, d22＝-2.2pm/V，d310.08 pm/V; the phase matching angle is 29.4 degrees when the 800nm frequency multiplication generates 400nm, and the formula shows that deffAbsolute value is in
Figure BDA0002635732670000032
Taking 0 degree to obtain the minimum value of 0.04pm/V,
Figure BDA0002635732670000033
the maximum value was 1.95pm/V at 30 degrees. By cutting and adjusting BBO crystals, different selection is made
Figure BDA0002635732670000034
Value deffThe absolute value is arbitrarily selected in the range of 0.04-1.95 pm/V.
The simulation of utilizing BBO crystal of different thickness to input light production frequency doubling light, wherein the parameter of input light is: the wavelength is 800nm, the pulse energy is 1mJ, the pulse width is 35fs, the spectral bandwidth is 26.9nm, and the spot size full width at half maximum is 3 mm. Wherein FIG. 2(A1) shows the crystal thickness 1mm, deffWhen the absolute value takes 0.7pm/V, the time domain intensity curves of the output fundamental frequency light and the frequency doubling light are obtained; FIG. 2(A2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 2 (A1); FIG. 2(B1) shows the thickness of the crystal being 3mm, deffWhen the absolute value takes 0.35pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 2(B2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 2 (B1); FIG. 2(C1) shows the thickness of the crystal, d, being 6mmeffWhen the absolute value takes 0.25pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; fig. 2(C2) corresponds to the frequency domain intensity curve of the frequency doubled light in fig. 2 (C1). As can be seen from FIG. 2, as the thickness of the nonlinear crystal BBO increases, a smaller d is selectedeffValue to ensure higher conversion efficiency and the sameTime domain widening and spectral bandwidth narrowing of the frequency doubled light are realized.
Example 2 laser pulses with a center wavelength of 1030nm, pulse energy of 10 muJ, pulse width of 35fs, spectral bandwidth of 44.6nm, spot size of 0.5mm full width at half maximum were converted into broad-width, narrow-bandwidth, doubled light pulses using BBO crystals
Utilizing BBO crystals with different thicknesses to carry out frequency doubling simulation results on input light, wherein input light parameters are as follows: the wavelength is 1030nm, the pulse energy is 10 muJ, the pulse width is 35fs, the spectral bandwidth is 44.6nm, and the spot size full width at half maximum is 0.5 mm. FIG. 3(A1) shows the thickness of the crystal, deffWhen the absolute value takes 2.01pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 3(A2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 3 (A1); FIG. 3(B1) shows the thickness of the crystal, d, being 0.6mmeffWhen the absolute value takes 1.6pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 3(B2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 3 (B1); FIG. 3(C1) shows the thickness of the crystal being 3mm, deffWhen the absolute value takes 0.55pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; fig. 3(C2) corresponds to the frequency domain intensity curve of the frequency doubled light in fig. 3 (C1).
Example 3 laser pulses with a center wavelength of 1030nm, a pulse energy of 50 muJ, a pulse width of 190fs, a spectral bandwidth of 8.2nm, and a spot size of 1mm full width at half maximum were converted into broad-and narrow-bandwidth doubled light pulses using BBO crystals
Utilizing BBO crystals with different thicknesses to carry out frequency doubling simulation results on input light, wherein input light parameters are as follows: the wavelength is 1030nm, the pulse energy is 50 muJ, the pulse width is 190fs, the spectral bandwidth is 8.2nm, and the spot size full width at half maximum is 1 mm. FIG. 4(A1) shows the crystal thickness 1.5mm, deffWhen the absolute value takes 2.01pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 4(A2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 4 (A1); FIG. 4(B1) shows a crystal thickness of 6mm, deffWhen the absolute value takes 0.8pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 4(B2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 4 (B1); FIG. 4(C1) shows the thickness of the crystal 10mm, deffWhen the absolute value takes 0.6pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; drawing (A)4(C2) corresponds to the frequency domain intensity curve for the doubled light in FIG. 4 (C1).
Example 4 laser pulses with a center wavelength of 1035nm, pulse energy of 20 muJ, pulse width of 350fs, spectral bandwidth of 4.5nm, spot size full width at half maximum of 2mm were converted into wide-pulse width, narrow-bandwidth, doubled light pulses using BBO crystals
Utilizing BBO crystals with different thicknesses to carry out frequency doubling simulation results on input light, wherein input light parameters are as follows: wavelength 1035nm, pulse energy 20 muJ, pulse width 350fs, spectral bandwidth 4.5nm, spot size full width at half maximum 2 mm. FIG. 5(A1) shows the thickness of the crystal being 3mm, deffWhen the absolute value takes 2pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 5(A2) corresponds to the frequency domain intensity curve of the doubled light of FIG. 5 (A1); FIG. 5(B1) shows the thickness of the crystal 10mm, deffWhen the absolute value takes 1pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; FIG. 5(B2) is a graph corresponding to the frequency domain intensity of the doubled light of FIG. 5 (B1); FIG. 5(C1) shows the thickness of the crystal 20mm, deffWhen the absolute value takes 0.6pm/V, the time domain intensity curve of the output fundamental frequency light and frequency doubling light; fig. 5(C2) corresponds to the frequency domain intensity curve of the doubled light in fig. 5 (C1).

Claims (5)

1. A method of second harmonic bandwidth compression, comprising: placing the nonlinear crystal on a rotating bracket, injecting the narrow-pulse wide-bandwidth spectrum fundamental frequency light generated by a pulse laser into the nonlinear crystal, and adjusting the fundamental frequency light around the optical axis of the crystal
Figure FDA0002635732660000011
Axial and wave vector
Figure FDA0002635732660000012
The normal line of the formed Zk plane rotates a polar angle to realize phase matching; in a direction perpendicular to the Zk plane and passing
Figure FDA0002635732660000013
An in-plane rotation of the shaft changes the azimuth angle; and continuously optimizing polar angle and azimuth angle to finally realize wide pulse width and narrow bandAnd outputting the broad frequency doubling laser.
2. The method of second harmonic bandwidth compression as claimed in claim 1 wherein the fundamental light is a pulsed laser output femtosecond laser.
3. The method of second harmonic bandwidth compression as claimed in claim 1 wherein the frequency doubled laser is a femtosecond laser or a picosecond laser.
4. The method of second harmonic bandwidth compression of claim 1 wherein the nonlinear crystal is a uniaxial crystal.
5. The method of second harmonic bandwidth compression of claim 4 wherein the uniaxial crystal is β -BaB2O4。
CN202010824695.0A 2020-08-17 2020-08-17 Second harmonic bandwidth compression method Pending CN111913332A (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04107434A (en) * 1990-08-28 1992-04-08 Pioneer Electron Corp Optical nonlinearity generating device
JPH10239721A (en) * 1997-02-28 1998-09-11 Rikagaku Kenkyusho High-speed wavelength converting device
CN101572382A (en) * 2008-04-30 2009-11-04 中国科学院理化技术研究所 Laser type I phase matching non-linear sum frequency device
CN102707542A (en) * 2012-06-04 2012-10-03 中国科学院上海光学精密机械研究所 Method for regulating best matching state of type-II KDP (Potassium Dihydrogen Phosphate) crystal for frequency multiplication of infrared light
CN109283769A (en) * 2018-11-26 2019-01-29 山东大学 A kind of broadband SHG quartz crystal device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04107434A (en) * 1990-08-28 1992-04-08 Pioneer Electron Corp Optical nonlinearity generating device
JPH10239721A (en) * 1997-02-28 1998-09-11 Rikagaku Kenkyusho High-speed wavelength converting device
CN101572382A (en) * 2008-04-30 2009-11-04 中国科学院理化技术研究所 Laser type I phase matching non-linear sum frequency device
CN102707542A (en) * 2012-06-04 2012-10-03 中国科学院上海光学精密机械研究所 Method for regulating best matching state of type-II KDP (Potassium Dihydrogen Phosphate) crystal for frequency multiplication of infrared light
CN109283769A (en) * 2018-11-26 2019-01-29 山东大学 A kind of broadband SHG quartz crystal device

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Application publication date: 20201110