阅读说明：本技术 一种圆偏或椭偏高次谐波的产生和调节方法及装置 (Method and device for generating and adjusting circular polarization or elliptical polarization higher harmonic ) 是由 兰鹏飞 邵任之 翟春洋 陆培祥 于 2019-09-03 设计创作，主要内容包括：本发明公开一种圆偏或椭偏高次谐波的产生和调节方法及装置。该方法利用两束不同频率的线性偏振光驱动气体介质辐射高次谐波,通过调节双色场的相对相位,保证辐射高次谐波的效率；通过调节双色场的偏振夹角和强度比,调节辐射高次谐波的椭偏率,使得在合适偏振夹角和强度比下,辐射出的奇次、偶次高次谐波强度出现明显差异,而且奇次和偶次高次谐波分别具有相同旋性,可以用于合成高效率的圆偏或椭偏阿秒脉冲。这是一种具有实用性的产生和调节相干极紫外光椭偏率的方法。(The invention discloses a method and a device for generating and adjusting circular polarization or elliptic polarization higher harmonics. The method utilizes two beams of linear polarized light with different frequencies to drive a gas medium to radiate higher harmonics, and ensures the efficiency of radiating the higher harmonics by adjusting the relative phase of a bicolor field; by adjusting the polarization angle and the intensity ratio of the bicolor field, the ellipsometry of the radiated higher harmonic is adjusted, so that the intensities of the odd harmonic and the even harmonic which are radiated are obviously different under the proper polarization angle and intensity ratio, and the odd harmonic and the even harmonic respectively have the same rotation property and can be used for synthesizing high-efficiency circular polarization or ellipsometric attosecond pulses. This is a practical method of generating and adjusting the ellipsometry of coherent extreme ultraviolet light.)

1. A method for generating and adjusting circular polarization or elliptical polarization higher harmonic waves is characterized by comprising the following steps:

step S0, radiating circular polarization or elliptic polarization higher harmonic waves through interaction of the bicolor field and the gas;

step S1, adjusting the efficiency of the higher harmonic by adjusting the relative phase of the two-color field;

and S2, fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, and adjusting the ellipsometry of the higher harmonic by adjusting the polarization angle and the intensity ratio of the bicolor field.

2. The method for generating and tuning circular polarized or elliptical polarized higher harmonics according to claim 1, wherein said step S2 comprises the following steps:

fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, keeping the intensity ratio of the bicolor field unchanged, adjusting the polarization included angle of the bicolor field, and adjusting the higher harmonic ellipsometry when the different polarization included angles of the bicolor field are different;

fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, keeping the polarization included angle of the bicolor field unchanged, adjusting the intensity ratio of the bicolor field, and adjusting the higher harmonic ellipsometry of the bicolor field at different intensity ratios.

3. The method for generation and tuning of circular polarization or elliptical polarization higher harmonic waves according to claim 1 or 2, wherein the higher harmonic waves are generated by the interaction of femtosecond laser with gas atoms or molecules, the gas atoms being one of rare gases, the gas molecules being one of diatomic or polyatomic molecular gases; the double-color field is generated by femtosecond laser after passing through a frequency doubling crystal.

4. The method for generation and tuning of circularly polarized or elliptically polarized higher harmonics according to claim 1 or 2, characterized in that the ellipticity of the higher harmonics is analyzed by means of an ultraviolet polarization analyzer; the ultraviolet polarization analyzer is composed of a reflecting mirror with different reflectivities for s-polarized light and p-polarized light.

5. A device for generating and adjusting circular or elliptical higher harmonics, comprising: the device comprises a beta-phase barium metaborate crystal, a first wedge-shaped mirror, a second wedge-shaped mirror, a first dichroic half-wave plate, a wire grid polarizing plate, a second dichroic half-wave plate, a focusing mirror and a gas nozzle;

the generation process of circular polarization or elliptical polarization higher harmonic wave is as follows: generating a frequency doubling field after the base frequency field passes through the beta-phase barium metaborate crystal, wherein the frequency doubling field and the base frequency field penetrating through the beta-phase barium metaborate crystal form a bicolor field; the double-color field sequentially enters a first wedge-shaped mirror, a second wedge-shaped mirror, a first double-color half-wave plate, a wire grid polarizer and a second double-color half-wave plate which are coaxially arranged; the first and second dichroic half-wave plates have the same model, each is a half-wave plate relative to the fundamental frequency field, and is a full-wave plate relative to the frequency doubling field; the focusing mirror is used for focusing the bicolor field emitted from the second bicolor half-wave plate and emitting the focused bicolor field to the gas nozzle; the gas nozzle is used for spraying gas, and the gas interacts with the focused two-color field to radiate circular polarization or elliptic polarization higher harmonic;

the adjustment process of circular polarization or elliptical polarization higher harmonic waves comprises the following steps: adjusting the relative phase between the fundamental frequency field and the frequency doubling field by adjusting the insertion depth of the second wedge-shaped mirror; controlling the intensity ratio of the fundamental frequency field and the frequency doubling field by rotating the first dichroic half-wave plate; controlling a polarization included angle between the fundamental frequency field and the frequency doubling field by rotating the second dichroic half-wave plate; the efficiency of the higher harmonic is regulated and controlled by regulating the relative phase, the ellipsometry of the higher harmonic is regulated and controlled by regulating the intensity ratio and the polarization included angle, and the ellipsometry of the higher harmonic is regulated while the relative phase is kept unchanged when the higher harmonic is at the highest efficiency.

6. The apparatus for generation and adjustment of circular polarized or elliptical higher harmonics according to claim 5, further comprising: calcite;

the calcite is placed at any position between the beta-phase barium metaborate crystal and the focusing mirror and is used for compensating group velocity dispersion between a fundamental frequency field and a frequency doubling field in the whole optical path.

7. The device for generation and regulation of circular polarized or elliptical higher harmonics according to claim 5 or 6, further comprising: an ultraviolet polarization analyzer;

the ultraviolet polarization analyzer is used for analyzing the ellipsometry of the higher harmonic; the ultraviolet polarization analyzer is composed of a reflecting mirror with different reflectivities for s-polarized light and p-polarized light.

8. The device for generation and regulation of circular polarized or elliptical higher harmonics according to claim 5 or 6, further comprising: a slit, a grating and a microchannel plate;

the slit, grating and microchannel plate combination is used for detecting the higher harmonics.

Technical Field

The invention relates to the technical field of ultrafast lasers, in particular to a method and a device for generating and adjusting circular polarization or elliptic polarization higher harmonics.

Background

The generation and application of attosecond pulses are a new field being developed by people. The attosecond coherent extreme ultraviolet light pulse synthesis technology research based on the higher harmonic wave has great application value in the fields of detection of atoms, intramolecular electron motion, atomic nucleus structures and the like, and can create unprecedented extreme experimental environments and provide unprecedented research conditions in the fields of ultrafast information, material science, life science and the like.

In 2001, scientists first experimentally synthesized euv pulses (m.hentschel, et al, Nature 414,509(2001)) with a pulse width of 650 attosecond by higher harmonics, indicating that the ultra-fast laser technology has progressed into the attosecond regime. Over a decade of rapid development, scientists now obtain attosecond pulses with a shortest pulse width of 43 attosecond (t. gaumnitz, et al, Optics Express 25,27506 (2017)). These studies, while largely deepening the understanding of attosecond light source generation, mostly focused on how attosecond pulses are generated and how pulse widths are compressed, neglecting the measurement and regulation of attosecond pulse ellipsometry. In the application aspect of attosecond pulse, circular polarization or elliptical polarization attosecond pulse has unique advantages in the fields of chiral molecule identification, magnetic material structure research by utilizing magnetic circular dichroism, attosecond pulse magnetic field generation and the like.

Thus, in recent years scientists have been working on how to generate higher harmonics that are circularly or elliptically polarized. Two representative schemes are to use a bicolor circular polarization technology (a. fleischer, et al., Nature photonics8,543(2014)), and a monochromatic non-collinear circular polarization technology (d.d. hickstein, et al., Nature photonics9,743 (2015)). The driving light used by the bicolor circular polarization technology is composed of two beams of circular polarized light with the same propagation direction, opposite rotation and different frequencies, and the bicolor circular polarized light presents a Lissajous figure structure with multiple symmetries in the polarization plane, namely a multi-lobe structure in each fundamental frequency oscillation period. The harmonics radiated by the bicolor circular polarization are circularly or elliptically polarized in each order, but the adjacent harmonics are opposite in rotation, so that the resultant attosecond pulse is linearly polarized. The driving light used by the monochromatic non-collinear circular polarization technology is formed by two beams of circular polarization light which has a certain included angle in the transmission direction and opposite rotation property and has the same frequency, the monochromatic non-collinear circular polarization light presents linear polarization in the intersection overlapping area of the two beams of light, the polarization direction is continuously changed on the transverse section, higher harmonics can be radiated and the circular polarization is generated by diffraction superposition in a far field, but the intersection overlapping area of the two beams of non-collinear light is limited, and therefore the radiation higher harmonics efficiency is lower.

For circular polarization or ellipsometric attosecond technology, the current problem is that in the existing methods for generating circular polarization or ellipsometric higher harmonics, either the radiated higher harmonics of different orders exhibit opposite helicity, so that the synthetic attosecond pulse is still linearly polarized; or the higher harmonic efficiency of radiation is low, and the energy of the synthetic attosecond pulse is limited, so that the application and development of the circular polarized or elliptical polarized attosecond pulse in practice are restricted.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to solve the problem that in the existing method for generating circular polarization or elliptic polarization higher harmonics, the radiated higher harmonics with different orders show opposite rotation, so that the synthesized attosecond pulse is still linearly polarized; or the higher harmonic efficiency of radiation is low, so that the technical problem of synthesizing the energy of attosecond pulses is limited.

To achieve the above object, in a first aspect, the present invention provides a method for generating and adjusting circular polarization or elliptic polarization higher harmonics, comprising the steps of:

step S0, radiating circular polarization or elliptic polarization higher harmonic waves through interaction of the bicolor field and the gas;

step S1, adjusting the efficiency of the higher harmonic by adjusting the relative phase of the two-color field;

and S2, fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, and adjusting the ellipsometry of the higher harmonic by adjusting the polarization angle and the intensity ratio of the bicolor field.

Optionally, the step S2 specifically includes the following steps:

fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, keeping the intensity ratio of the bicolor field unchanged, adjusting the polarization included angle of the bicolor field, and adjusting the higher harmonic ellipsometry when the different polarization included angles of the bicolor field are different;

fixing the relative phase of the bicolor field at the corresponding relative phase when the highest-efficiency higher harmonic is obtained, keeping the polarization included angle of the bicolor field unchanged, adjusting the intensity ratio of the bicolor field, and adjusting the higher harmonic ellipsometry of the bicolor field at different intensity ratios.

Optionally, the higher harmonic is generated by interaction of femtosecond laser and gas atoms or molecules, wherein the gas atoms are one of rare gases, and the gas molecules are one of diatomic or polyatomic molecular gases; the double-color field is generated by femtosecond laser after passing through a frequency doubling crystal.

Optionally, analyzing the ellipsometry of the higher harmonic by an ultraviolet polarization analyzer; the ultraviolet polarization analyzer is composed of a reflecting mirror with different reflectivities for s-polarized light and p-polarized light.

In a second aspect, the present invention provides a device for generating and adjusting circularly polarized or elliptically polarized higher harmonics, comprising: the device comprises a beta-phase barium metaborate crystal, a first wedge-shaped mirror, a second wedge-shaped mirror, a first dichroic half-wave plate, a wire grid polarizing plate, a second dichroic half-wave plate, a focusing mirror and a gas nozzle;

the generation process of circular polarization or elliptical polarization higher harmonic wave is as follows: generating a frequency doubling field after the base frequency field passes through the beta-phase barium metaborate crystal, wherein the frequency doubling field and the base frequency field penetrating through the beta-phase barium metaborate crystal form a bicolor field; the double-color field sequentially enters a first wedge-shaped mirror, a second wedge-shaped mirror, a first double-color half-wave plate, a wire grid polarizer and a second double-color half-wave plate which are coaxially arranged; the first and second dichroic half-wave plates have the same model, each is a half-wave plate relative to the fundamental frequency field, and is a full-wave plate relative to the frequency doubling field; the focusing mirror is used for focusing the bicolor field emitted from the second bicolor half-wave plate and emitting the focused bicolor field to the gas nozzle; the gas nozzle is used for spraying gas, and the gas interacts with the focused two-color field to radiate circular polarization or elliptic polarization higher harmonic;

the adjustment process of circular polarization or elliptical polarization higher harmonic waves comprises the following steps: adjusting the relative phase between the fundamental frequency field and the frequency doubling field by adjusting the insertion depth of the second wedge-shaped mirror; controlling the intensity ratio of the fundamental frequency field and the frequency doubling field by rotating the first dichroic half-wave plate; controlling a polarization included angle between the fundamental frequency field and the frequency doubling field by rotating the second dichroic half-wave plate; the efficiency of the higher harmonic is regulated and controlled by regulating the relative phase, the ellipsometry of the higher harmonic is regulated and controlled by regulating the intensity ratio and the polarization included angle, and the ellipsometry of the higher harmonic is regulated while the relative phase is kept unchanged when the higher harmonic is at the highest efficiency.

Optionally, the apparatus further comprises: calcite;

the calcite is placed at any position between the beta-phase barium metaborate crystal and the focusing mirror and is used for compensating group velocity dispersion between a fundamental frequency field and a frequency doubling field in the whole optical path.

Optionally, the apparatus further comprises: an ultraviolet polarization analyzer;

the ultraviolet polarization analyzer is used for analyzing the ellipsometry of the higher harmonic; the ultraviolet polarization analyzer is composed of a reflecting mirror with different reflectivities for s-polarized light and p-polarized light.

Optionally, the apparatus further comprises: a slit, a grating and a microchannel plate;

the slit, grating and microchannel plate combination is used for detecting the higher harmonics.

Specifically, the slit is used for shaping the higher harmonic beam, the grating is used for spatially separating the higher harmonics of different frequency components and reflecting the higher harmonics to the microchannel plate, and the microchannel plate is used for amplifying the higher harmonic signal.

Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

Drawings

FIG. 1 is a diagram of an experimental apparatus for generating and adjusting coherent extreme ultraviolet ellipsometry using a non-parallel polarized dichromatic field according to the present invention;

FIG. 2(a) is a graph of the intensity of higher harmonics measured in different intensity ratios of the frequency-doubled field to the fundamental field according to the present invention;

FIG. 2(b) is a graph showing the result of normalizing the intensity of the higher harmonic in each ratio of the multiplied frequency field to the fundamental frequency field according to the present invention;

FIG. 3 is a diagram showing the polarization states of the higher harmonics of 14 th to 22 th order of the Ar atomic radiation measured by the present invention;

FIG. 4 is an ellipsograph of the 15 th and 16 th harmonics measured when the frequency doubling field and the fundamental field in the two-color field are at different polarization angles according to the present invention;

FIG. 5 is an ellipsograph of the 14 th to 23 rd harmonics of Ar atomic radiation under different intensity ratios of the frequency doubling field and the fundamental frequency field measured by the present invention;

FIG. 6(a) is an ellipsograph and rotation chart of Ar atom radiation higher harmonic waves obtained by theoretical simulation calculation under different intensity ratios of the frequency doubling field and the fundamental frequency field;

FIG. 6(b) is a graph showing the intensity ratio of the even harmonic to the odd harmonic in the frequency multiplication field and the fundamental field obtained by the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Aiming at the defects of the existing method for generating circular polarization or elliptic polarization higher harmonics, the invention aims to provide a method for generating and adjusting the elliptic polarization rate of higher harmonics, wherein the radiated odd and even higher harmonics have the same helicity respectively, and meanwhile, the method can ensure that the efficiency of the odd and even higher harmonics has obvious difference, and aims to break through the technical bottleneck that the synthesis of high-efficiency circular polarization or elliptic polarization attosecond pulses is limited because high-efficiency single-helicity higher harmonics cannot be obtained.

The invention provides a method for generating and adjusting coherent extreme ultraviolet ellipsometry by utilizing a non-parallel polarization bicolor field. The method is characterized in that firstly, the relative phase of a non-parallel polarization bicolor field is adjusted to ensure the radiation of high-efficiency higher harmonics, so that the synthesized attosecond pulse has higher energy; secondly, by adjusting the polarization included angle and the intensity ratio of the double-color field, the ellipsometry of the higher harmonic can be effectively adjusted, and the efficiency of odd and even higher harmonics has obvious difference. The odd or even higher harmonics in a wider range of frequency spectrum have the same rotation, and the synthesized high-energy attosecond pulse still has larger ellipticity.

The method comprises the following specific processes:

(1) and adjusting the relative phase of the bicolor field, and calibrating the relative phase with the highest radiation higher harmonic efficiency.

(2) And adjusting the polarization included angle of the bicolor field, and detecting the change rule of the ellipsometry of the higher harmonic along with the polarization included angle.

(3) And adjusting the intensity ratio of the bicolor field, and detecting the change relation of the higher harmonic ellipsometry with the intensity ratio.

The ellipsometry of the higher harmonic is measured in the experiment by an ultraviolet polarization analyzer, and the circularity of the ellipsometric higher harmonic is calculated by a strong field approximation theoretical model.

As shown in fig. 1, the present invention provides a method for generating and adjusting ellipsometry of extreme ultraviolet light using linearly polarized bichromatic light, comprising the steps of:

(1) and (4) building an experimental light path. As shown in FIG. 1, the fundamental frequency field passes through beta-phase barium metaborate (beta-BaB)₂O₄BBO) crystal to generate frequency doubling field, calcite to compensate group velocity dispersion between fundamental frequency field and frequency doubling field in whole optical path, first wedge mirror and second wedge mirrorThe dual-color gas nozzle is used for adjusting the relative phase between a fundamental frequency field and a frequency doubling field, the first dual-color half-wave plate and the wire grid polarizer are combined to adjust the intensity of the fundamental frequency field, the second dual-color half-wave plate is used for adjusting the polarization included angle between the fundamental frequency field and the frequency doubling field, the dual-color field interacts with gas sprayed out of the gas nozzle after being focused by the focusing mirror to radiate higher harmonics, the ultraviolet polarization analyzer is used for detecting the polarization state of the higher harmonics, and the slit, the grating and the micro-channel plate assembly are combined to detect higher harmonic signals.

(2) The intensity ratio of the fundamental frequency field and the frequency doubling field can be changed by adjusting the angle of the first dichroic half-wave plate relative to the wire grid polarizer; the polarization angle of the fundamental frequency field and the frequency doubling field can be changed by adjusting the angle of the second dichroic half-wave plate relative to the wire grid polarizer. And then, higher harmonic signals of fundamental frequency fields and frequency doubling fields in different intensity ratios and different polarization included angles can be detected on the microchannel plate.

(3) And detecting the polarization state of the higher harmonic by an ultraviolet polarization analyzer. According to Malus' law, the intensity of a beam of principal axes is I₀The light intensity of the polarized light with the ellipsometry of epsilon after passing through the ultraviolet polarization analyzer can be expressed as:

wherein phi represents the included angle between the optical axis of the ultraviolet polarization analyzer and the polarization main axis of the light beam, R_sAnd R_pRespectively, the reflectivity of the uv polarization analyzer for the s and p polarization components of the beam. According to the formula, the intensity change of the light beam and the minimum value I of the light intensity can be detected by rotating the angle of the ultraviolet polarization analyzer_minAnd maximum value I_maxCan be expressed as:

I_min＝(R_p+R_s·ε²)·I₀

and:

I_max＝(R_s+R_p·ε²)·I₀

(4) determination of R by measuring linear polarization_p/R_sA ratio. When the beam is linearly polarized, epsilon is 0,

from the step (3), the extinction ratio R of the ultraviolet polarization analyzer to the p-and s-polarized components of the light beam_p/sComprises the following steps:

(5) extracting the light beam ellipsometry. Combining the steps (3) and (4), the ellipsometry epsilon can be obtained as follows:

wherein R is an intermediate amount,

(6) by repeating the above operations (2) - (5), the ellipsometry of the extreme ultraviolet light was adjusted and measured.

The present invention will be further explained by taking the higher harmonic waves radiated by the interaction of the femtosecond laser and the Ar atoms as an embodiment with reference to the attached drawings:

in the following description, the fundamental wavelength of the two-color field is 800nm, and the frequency doubling wavelength is 400nm, which are only used as examples, and the wavelength of the two-color field is not limited at all.

In one embodiment of the present invention, as shown in fig. 1, a bundle of fundamental frequency fields with a center wavelength of 800nm, a pulse width of 35fs, and a repetition frequency of 1kHz passes through BBO to generate a frequency doubling field with a center wavelength of 400 nm. Calcite of different thicknesses was used to compensate for group velocity dispersion between 400nm and 800nm throughout the optical path, and sum frequency BBO (not shown) was used to observe the 266nm sum frequency signal at the gas nozzle, ensuring that 400nm and 800nm coincide in the time domain. The insertion depth of the second wedge-shaped mirror is adjusted to make the relative phase of 400nm and 800nm be 0.5 pi, namely the position where the higher harmonic signal is most intense. The intensity ratio of 400nm to 800nm is controlled by adjusting the first dichroic half-wave plate, and the polarization included angle of 400nm to 800nm is controlled to be changed between 0 and 90 degrees by adjusting the second dichroic half-wave plate. Ar atomic gas is introduced into the vacuum chamber through an air nozzle with the diameter of 250 mu m, and interacts with the bicolor field to radiate higher harmonics. The generated higher harmonic is diffracted by the grating and then displayed on a display screen of the microchannel plate. The ultraviolet polarization analyzer composed of three gold-plated film reflectors is arranged on a rotating device, the rotation angle of the ultraviolet polarization analyzer is controlled by an electric control rotating platform, and the rotating platform is adjusted to measure the intensity change of the higher harmonic signals. Specifically, sum frequency BBO belongs to one of BBOs.

FIG. 2(a) shows the harmonic signals of different intensity ratios of 400nm and 800nm driving lights, the order of the harmonic is 14 to 23, and the ratio of the 400nm to 800nm driving light intensity is 0.1:1 to 1.6: 1. FIG. 2(b) shows higher harmonic spectra at 400nm to 800nm driving light intensity ratios of 0.1:1, 0.4:1, 0.7:1, 1.0:1, 1.3:1 and 1.6:1, with normalization of the higher harmonic spectra at each intensity ratio.

FIG. 3 shows the polarization states of the 14 th to 22 th higher harmonics of the Ar atomic radiation at a driving light intensity ratio of 1.3:1 of 400nm to 800nm measured by the present invention, wherein the solid line is drawn by ellipsometry extracted from experimental data, and the error bar indicates the accuracy in the experimental measurement. In FIG. 3, H denotes the higher harmonics, and H14-H22 indicate the 14 th to 22 th harmonics, respectively.

FIG. 4 shows ellipsometry of the 15 th and 16 th harmonics of the 400nm and 800nm driving light at different polarization angles when the ratio of the 400nm to 800nm driving light intensity measured by the present invention is 1.3:1, and the error bars show the accuracy in the experimental measurement. The ellipsometry of the higher harmonic wave is gradually increased as the included angle between the polarization of the 400nm driving light and the polarization of the 800nm driving light changes from 0 degree to 90 degrees.

FIG. 5 shows ellipsoids of 14 th to 23 th harmonics of Ar atomic radiation at different intensity ratios of 400nm and 800nm when the polarization included angle of the driving lights of 400nm and 800nm measured by the present invention is 80 degrees, and the size of the shaded area shows the accuracy in the experimental measurement. The ellipsometry of the higher harmonics increases gradually with increasing ratio of 400nm to 800nm driving light intensity.

FIG. 6(a) shows the ellipsometry of the higher harmonics at 400nm to 800nm driving light intensity ratios of 1.0:1, 1.3:1, and 1.6:1, with the signs of the ellipsometry indicating handedness to the right and left, respectively, as calculated in theoretical simulations. FIG. 6(b) is the intensity ratio of the even harmonic to the odd harmonic obtained by the present invention at different intensity ratios of 400nm and 800nm driving light, wherein the even harmonic is the sum of the intensities of the 14 th, 16 th, 18 th, 20 th and 22 th harmonics, and the odd harmonic is the sum of the intensities of the 15 th, 17 th, 19 th, 21 th and 23 th harmonics. The scatter points represent experimental measurement results, the error bars represent experimental measurement accuracy, and the dotted lines represent theoretical simulation calculation results.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.