Method for generating a nonlinear optical effect

Abstract

The application provides a nonlinear optical effect generation method, relates to the field of optoelectronic technology, and comprises the following steps: fixing and placing a polar ion crystal as a nonlinear medium, the polar ion crystal being a diatomic crystal or a polyatomic crystal with an optical phonon mode; using a modulated terahertz wave to excite a stimulated phonon polariton in the nonlinear medium, so as to enhance the nonlinear efficiency of signal light incident on the nonlinear medium; and adjusting the polarization angle and the incident angle of the signal light and / or the modulated terahertz wave, so as to generate a nonlinear optical effect. The application is based on the characteristics of the interaction between light and matter modulated by the stimulated phonon polariton, and the nonlinear polarizability is greatly improved by using the stimulated phonon polariton, so that the weak light nonlinear effect of most wavelengths of light can be realized efficiently; and the nonlinear optical effect has the advantages of high refresh rate, wide spectral response, low threshold and low power consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronics, in particular to a method for generating nonlinear optical effect. BACKGROUND

[0002] Nonlinear optical effect is the core principle of many optical and photonic technologies including spectral measurement, light source system, photoelectric conversion, light control, optical communication, optical storage, optical computing, etc. Developing nonlinear optical effect generation method helps to further develop nonlinear spectral technology, optical precision measurement, nonlinear optical switch, nonlinear optical computing and other technologies, thereby bringing huge economic and social benefits. Existing nonlinear optical effect generation methods mainly rely on the nonlinear polarization of electrons in the material, mainly including two categories: one is to use the instantaneous nonlinear response of electrons to achieve a very fast nonlinear effect refresh rate, which is about femtosecond, but the efficiency is very low, and the effective second-order nonlinear susceptibility is about 10 -12 m / V to 10 -10 m / V, and the third-order nonlinear susceptibility is about 10 -19 m 2 / V 2 to 10 -17 m 2 / V 2 ; the other is a weak light nonlinear effect based on the accumulation of electron nonlinear polarization, and the typical representative is photorefractive effect, which has higher nonlinear efficiency, but the refresh time is between several milliseconds and several days. Some emerging nonlinear optical effect generation methods are based on organic materials and two-dimensional materials, etc. Although these methods have higher generation efficiency, the material itself is unstable, the refresh time is also unstable, and the industrial transformation is difficult.

[0003] Therefore, how to realize high stability, high refresh rate and wide spectral response of nonlinear optical effect has become a technical problem to be solved. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art or related art, and discloses a method for generating nonlinear optical effect, which can realize high stability, high refresh rate and wide spectral response of nonlinear optical effect in extreme environment.

[0005] The present application discloses a method for generating nonlinear optical effect, comprising: fixing and placing a polar ion crystal as a nonlinear medium, the polar ion crystal being a diatomic crystal or a polyatomic crystal with optical phonon mode; using a modulated terahertz wave to excite stimulated phonon polariton in the nonlinear medium to enhance the nonlinear efficiency of signal light incident on the nonlinear medium; and adjusting the polarization angle and the incident angle of the signal light and / or the modulated terahertz wave to generate nonlinear optical effect.

[0006] Preferably, the method further comprises receiving the emitted signal light by a detection device, wherein the detection device comprises a spectrometer, a quantitative time-resolved imaging system, a power meter equipped with a monochromator, an interferometer or a photoelectric coupling instrument.

[0007] Preferably, the signal light is a femtosecond laser, and the modulated terahertz wave is generated by rectification of the femtosecond laser in the nonlinear medium.

[0008] Preferably, the modulated terahertz wave is emitted by a terahertz light source, the signal light is emitted by a signal light source, and the modulated terahertz wave and the signal light are simultaneously irradiated on the nonlinear medium.

[0009] Preferably, the femtosecond laser is a pulsed laser with a pulse width of 10-300 fs from ultraviolet to near infrared.

[0010] Preferably, the signal light source is a continuous laser or a pulsed laser with a wavelength from ultraviolet to far infrared.

[0011] Preferably, the frequency of the modulated terahertz light source is 0.1-30 terahertz.

[0012] Preferably, the nonlinear medium is a lithium niobate or lithium tantalate crystal, and the material specifications include a thin film with a thickness of less than 10 microns, a wafer with a thickness of 10-500 microns, and a square, wedge, column or spherical block material with a thickness of more than 500 microns.

[0013] Preferably, the nonlinear optical effect includes sum frequency generation, difference frequency generation, second harmonic generation, optical rectification, Pockels effect, parametric amplification, parametric oscillation, parametric up-conversion, parametric down-conversion, third harmonic generation, Kerr effect, phase conjugation, two-photon absorption, saturated absorption, inverse saturated absorption, self-focusing, self-phase modulation, cross-phase modulation, Raman scattering or high harmonic generation.

[0014] Preferably, the polarization and incident angle of the signal light and the modulated terahertz wave are determined by the phase matching condition of the specific nonlinear optics, and specifically, the transmission speed of the signal light and the terahertz wave along the transmission direction is equal.

[0015] The beneficial effects of the present application at least include: modulated terahertz light is used to generate stimulated phonon polaritons, thereby improving the nonlinear efficiency, which can greatly improve the nonlinear efficiency of the signal light while ensuring the high refresh rate of the order of picoseconds, and the corresponding second-order nonlinear susceptibility can reach 10 -6 m / V to 10 -5 m / V, the third-order nonlinear susceptibility can reach 10 - 15 m 2 / V 2 to 10 -13 m 2 / V 2 ; due to the use of a polar ionic crystal, the material properties are more stable, and can be used in extreme environments; in addition, the present application also has the advantages of simple device, easy maintenance, low cost, easy to obtain materials, high efficiency, fast refresh

[0016] , which can provide guarantee for the further development of weak light nonlinear spectroscopy, optical precision measurement, nonlinear control of phonon polariton quantum bits, nonlinear optical computing and other technologies. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The structure schematic diagram of the nonlinear optical effect generating device according to one embodiment of the present application is shown.

[0018] 5 Figure 2 The structure schematic diagram of the nonlinear optical effect generating device according to another embodiment of the present application is shown.

[0019] Figure 3 The experimental principle diagram of the nonlinear optical effect generating device corresponding to Figure 2 is shown.

[0020] Figure 4 The nonlinear test result diagram of the femtosecond laser second harmonic according to the embodiment of the present application is shown.

[0021] 0 Figure 5 is an enlarged view of the portion shown in the dashed box. Figure 4 DETAILED DESCRIPTION

[0022] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0023] 5In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, however,

[0024] ​The application can also be implemented in other ways different from those described herein, and therefore the application is not limited to the specific embodiments disclosed below.

[0025] According to one embodiment of the application, a method for generating nonlinear optical effects is disclosed, comprising:

[0026] The polar ion crystal is fixedly placed as a nonlinear medium, and the polar ion crystal is a diatomic crystal or a polyatomic crystal with an optical phonon mode; a stimulated phonon polariton is excited in the nonlinear medium by modulating a terahertz wave to enhance the nonlinear efficiency of signal light incident on the nonlinear medium; and the polarization angle and the incident angle of the signal light and / or the modulating terahertz wave are adjusted to generate the nonlinear optical effect.

[0027] In this embodiment, the diatomic or polyatomic polar crystal has an optical vibration mode, specifically, a relative vibration of positive and negative ions, which can generate a spontaneous phonon polariton in the crystal. When an external terahertz modulation wave is incident, it will polarize and drive the atoms in the lattice and strongly couple with the optical phonon to generate a stimulated phonon polariton. At this time, the vibration of the atoms and electrons in the lattice is greatly modulated, the nonlinear polarizability is greatly increased, and a giant nonlinear effect is generated. For example, when the polar ion crystal is a lithium niobate crystal, it has multiple optical phonon vibration modes, and the optical phonon A1 soft mode of the lithium niobate crystal is used, specifically, the relative vibration between the niobium atom and the oxygen octahedron and the lithium atom along the optical axis direction, which can generate a spontaneous phonon polariton in the crystal. When an external terahertz modulation wave is incident, it will polarize and drive the atoms in the lattice and strongly couple with the optical phonon to generate a stimulated phonon polariton. At this time, the vibration of the atoms and electrons in the lattice is greatly modulated, the nonlinear polarizability is greatly increased, and a giant nonlinear effect is generated.

[0028] According to the above embodiment, preferably, when the signal light is a femtosecond laser, the modulating terahertz wave is generated by rectification of the femtosecond laser in the nonlinear medium.

[0029] According to the above embodiment, preferably, the modulating terahertz wave is emitted by a terahertz light source, and the signal light is emitted by a signal light source, and the modulating terahertz wave and the signal light are simultaneously irradiated on the nonlinear medium.

[0030] According to the above embodiment, preferably, the femtosecond laser is a titanium-doped sapphire femtosecond laser, which outputs a laser pulse beam with a center wavelength of 800 nm, a pulse width of 90 fs, and a repetition frequency of 1 kHz after regenerative amplification and dispersion compensation.

[0031] According to the above embodiment, preferably, the signal light source is a continuous laser or a pulsed laser with a wavelength from ultraviolet to far infrared.

[0032] According to the above embodiment, preferably, the frequency of the modulated terahertz light source is 0.1-30 terahertz.

[0033] According to the above embodiment, preferably, the nonlinear medium is a lithium niobate crystal or a lithium tantalate crystal, and the material specifications include a thin film with a thickness of less than 10 microns, a wafer with a thickness of 10-500 microns, and a square, wedge, column or spherical block with a thickness of more than 500 microns.

[0034] According to the above embodiment, preferably, the nonlinear optical effect includes sum frequency generation, difference frequency generation, second harmonic generation, optical rectification, Pockels effect, parametric amplification, parametric oscillation, parametric up-conversion, parametric down-conversion, third harmonic generation, Kerr effect, phase conjugation, two-photon absorption, saturated absorption, inverse saturated absorption, self-focusing, self-phase modulation, cross-phase modulation, Raman scattering or high-order harmonic generation. For example, when the signal light source is a pulsed laser with a central wavelength of 800 nm, a pulse width of 90 fs and a repetition frequency of 1 kHz, and the nonlinear medium is an x-cut lithium niobate wafer with a thickness of 50 microns, the nonlinear optical effect realized is the second harmonic generation of the signal light.

[0035] According to the above embodiment, preferably, the polarization and incident angle of the signal light and the modulated terahertz wave are determined by the phase matching condition of the specific nonlinear optics, which is embodied as the transmission speed of the signal light and the terahertz wave being equal in the transmission direction. For example, when the nonlinear medium is a lithium niobate crystal, the polarization and incident angle of the signal light and the modulated terahertz wave are both along the optical axis direction of the lithium niobate crystal, and the transmission speed of the modulated terahertz wave and the signal light in the lithium niobate crystal after being incident on the crystal is equal.

[0036] As Figure 1As shown, according to one embodiment of the present application, a device for generating nonlinear optical effect is disclosed, which comprises a signal light source, a signal light reflecting mirror 1, a signal light focusing mirror 2, a nonlinear crystal 3, a detector, a terahertz source, a terahertz reflecting mirror 4, and a terahertz focusing mirror 5. The signal light, under the action of the modulated terahertz wave, is affected by the stimulated phonon polariton, so that the giant nonlinear effect can be achieved. The phase matching requirement of the signal light is completely the same as that of the conventional nonlinear optics, which can be the phase matching achieved by using the material refractive index ellipsoid and dispersion characteristics, or quasi-phase matching. The modulated terahertz wave plays a role of exciting the stimulated phonon polariton and enhancing the nonlinear efficiency. The specific working process includes: using a polar ion crystal as the nonlinear crystal and fixing it; starting the signal light source and the terahertz source, and simultaneously irradiating the nonlinear crystal; adjusting the polarization and the incident angle of the signal light and the terahertz wave according to the specific nonlinear optical effect to be generated; and using the detector to receive the emitted nonlinear signal light. The nonlinear optical effect includes sum frequency generation, difference frequency generation, second harmonic generation, optical rectification, Pockels effect, parametric amplification, parametric oscillation, parametric up-conversion, parametric down-conversion, third harmonic generation, Kerr effect, phase conjugation, two-photon absorption, saturated absorption, inverse saturated absorption, self-focusing, self-phase modulation, cross-phase modulation, Raman scattering, or high harmonic generation. The polar ion crystal refers to a binary crystal and a multi-atomic crystal having an optical phonon mode, such as lithium niobate, and the material geometric shape is a thin film with a thickness of less than 10 microns, a wafer with a thickness of 10 to 500 microns, or a square, wedge, column, or spherical block material with a thickness of more than 500 microns.

[0037] According to the above embodiment, preferably, the signal light source is a continuous laser or a pulsed laser with a wavelength from ultraviolet to far infrared. After the terahertz wave is incident on the polar ion crystal, resonance occurs between the terahertz wave and the positive and negative ions in the crystal material, and then the stimulated phonon polariton is generated. At this time, the polarization of the positive and negative ions is greatly enhanced and enters the nonlinear polarization region, and then the environment of the electrons in the material is changed, and a great nonlinear polarizability is obtained.

[0038] According to the above embodiment, preferably, the terahertz source is various terahertz sources with a frequency from 0.1 to 30 terahertz, such as a quantum cascade laser, a microwave diode, a free electron laser, a photoconductive antenna, or generated by an ultrafast pulsed laser in a nonlinear material.

[0039] According to the above embodiment, preferably, the polarization and the incident angle of the signal light and the terahertz wave are determined by the phase matching condition of the specific nonlinear optics, and specifically embodied as that the transmission speed of the signal light along the transmission direction is equal to that of the terahertz wave.

[0040] As Figure 2As shown, according to another embodiment of the present invention, a device for generating nonlinear optical effects is disclosed, comprising: a femtosecond laser (femtosecond laser), a laser blazed grating 6, a laser achromatic convex lens 7, a nonlinear crystal 8, and a spectrometer. Figure 1 Compared to the disclosed structure, this embodiment uses a femtosecond laser as the signal light. The modulated terahertz wave can then be generated by rectifying the femtosecond laser in a nonlinear crystal. After the terahertz wave is generated, stimulated phonon polaritons are excited in the nonlinear crystal, which in turn modulate the nonlinear effect of the signal light. The femtosecond laser is a titanium-doped sapphire femtosecond laser manufactured by Spectra Physics. After regenerative amplification and dispersion compensation, it outputs a laser pulse beam with a center wavelength of 800 nm, a pulse width of approximately 90 fs, and a repetition frequency of 1 kHz. In the experiment, the laser output power was controlled at 400 mW. The grating used has a blaze angle of 26° and a diameter of 1200 mm. -1 A blazed grating, as shown in the figure, guides the -1st order diffracted light into the nonlinear crystal. The laser achromatic convex lens used has a diameter of 5.1 cm and a focal length of 5 cm. In the experiment, the distance between the grating and the lens (object distance) is approximately 22 cm, at which point the image plane is located approximately 1.5 cm behind the focal point. The nonlinear crystal used is an x-cut lithium niobate wafer. The wafer thickness is 50 micrometers, and its dimensions are 1 mm (y) × 1.1 mm (z). The selected target nonlinear effect is the second harmonic, and a fiber optic spectrometer is used as the detector.

[0041] Generally, the intensity of the terahertz wave generated by a femtosecond laser in a lithium niobate crystal is positively correlated with the intensity of the femtosecond laser. In the experiment, the laser was incident on the grating at an angle of 46°, corresponding to a -1st order diffraction angle of 20°. The purpose of using -1st order diffracted light is to change the wavefront of the femtosecond laser, thereby changing the propagation speed of the laser incident on the crystal, thus enabling strong generation of the terahertz wave at the grating image plane, and subsequently exciting stimulated phonon polaritons. At this point, the power density of the femtosecond laser is much lower than at the focal point. At the focal point, although the power density of the femtosecond laser is very high, due to phase mismatch, it is impossible to generate terahertz waves and stimulated phonon polaritons. The second harmonic signal generated at this point is not modulated (e.g., ...). Figure 3 As shown in the figure, the lithium niobate wafer is gradually moved from the image plane to near the focal plane, and the intensity change of the 400nm frequency-doubled signal is recorded using a spectrometer. The corresponding experimental results are as follows. Figure 4 and Figure 5The position "0" in the figure represents the image plane position, i.e. the second harmonic intensity under the action of the stimulated phonon polariton, and the position "15mm" represents the focusing position, at which the second harmonic is generated by the femtosecond laser focusing; the femtosecond laser second harmonic signal (image plane) based on the stimulated phonon polariton is about 1 / 8 of the traditional focusing signal (focal plane); according to the Gaussian beam focusing law, the light power density of the 800nm laser after focusing by a 5cm lens is about 1.35x10 6 times that of the 1.5cm position after focusing; therefore, the laser second harmonic based on the stimulated phonon polariton is about 4.8x10 5 times higher than the corresponding nonlinear polarizability of the traditional focusing.

[0042] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of generating a nonlinear optical effect, characterized by, The application relates to a method for generating nonlinear optical effect, comprising the following steps: placing a polar ion crystal as a nonlinear medium, the polar ion crystal being a diatomic crystal or a multiatomic crystal with optical phonon mode; using a modulated terahertz wave to excite a stimulated phonon polariton in the nonlinear medium, so as to enhance the nonlinear efficiency of signal light incident on the nonlinear medium; adjusting the polarization angle and the incident angle of the signal light and / or the modulated terahertz wave, so as to generate nonlinear optical effect.

2. The method of generating a nonlinear optical effect according to claim 1, wherein The application further comprises the following steps: using a detection device to receive the emitted signal light.

3. The method of generating a nonlinear optical effect according to claim 1, wherein The signal light is femtosecond laser, and the modulated terahertz wave is generated by rectification of the femtosecond laser in the nonlinear medium.

4. The method of generating a nonlinear optical effect according to claim 1, wherein A terahertz light source is used to emit the modulated terahertz wave, and a signal light source is used to emit the signal light, and the modulated terahertz wave and the signal light irradiate the nonlinear medium at the same time.

5. The method of generating a nonlinear optical effect according to claim 3, wherein The femtosecond laser is pulse laser with a wavelength from ultraviolet to near infrared and a pulse width of 10-300 fs.

6. The method of generating a nonlinear optical effect according to claim 4, wherein The signal light source is a continuous laser or a pulse laser with a wavelength from ultraviolet to far infrared.

7. The method of generating a nonlinear optical effect according to claim 4, wherein The frequency of the modulated terahertz light source is 0.1-30 terahertz.

8. The method of generating a nonlinear optical effect according to any one of claims 1 to 7, characterized in that, The nonlinear medium is lithium niobate or lithium tantalate crystal, and the material specifications include: a thin film with a thickness of less than 10 microns, a wafer with a thickness of 10-500 microns, and a square, wedge, column or spherical block material with a thickness of more than 500 microns.

9. The method of generating a nonlinear optical effect according to any one of claims 1 to 7, characterized in that, The nonlinear optical effect includes sum frequency generation, difference frequency generation, second harmonic generation, optical rectification, Pockels effect, parametric amplification, parametric oscillation, parametric up-conversion, parametric down-conversion, third harmonic generation, Kerr effect, phase conjugation, two-photon absorption, saturated absorption, inverse saturated absorption, self-focusing, self-phase modulation, cross-phase modulation, Raman scattering or high harmonic generation.

10. The method of generating a non-linear optical effect according to any one of claims 1 to 7, wherein The polarization and incident angle of the signal light and the modulated terahertz wave are determined by the phase matching condition of specific nonlinear optics, and specifically, the transmission speed of the signal light and the terahertz wave along the transmission direction is equal.

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