CN110471234B - Device and method for generating broadband optical radiation based on chirp nonlinear crystal - Google Patents
Device and method for generating broadband optical radiation based on chirp nonlinear crystal Download PDFInfo
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- CN110471234B CN110471234B CN201910794797.XA CN201910794797A CN110471234B CN 110471234 B CN110471234 B CN 110471234B CN 201910794797 A CN201910794797 A CN 201910794797A CN 110471234 B CN110471234 B CN 110471234B
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- G—PHYSICS
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- 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
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
- G02F1/3544—Particular phase matching techniques
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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
- G02F1/355—Non-linear optics characterised by the materials used
- G02F1/3551—Crystals
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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
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
- G02F1/3544—Particular phase matching techniques
- G02F1/3548—Quasi phase matching [QPM], e.g. using a periodic domain inverted structure
Abstract
The invention discloses a device and a method for generating broadband optical radiation based on a chirped nonlinear crystal, wherein the device is a synchronous pump optical parametric oscillator of a quasi-phase matching second-order nonlinear crystal designed based on a chirped period so as to generate broadband optical radiation; the quasi-phase matching second-order nonlinear crystal designed by the chirp period has different period lengths at different positions, and different periods correspond to phase matching at different wavelengths; when the pump light generated by the pump source passes through the crystal, different signal wavelengths are generated at different positions of the crystal; in addition, cavity mirrors are respectively arranged at the two ends of the crystal; the cavity has a dispersion function that provides dispersion to reduce the net dispersion in the cavity. Particularly, the quasi-phase matching second-order nonlinear crystal based on the chirp period design is adopted, so that compared with the prior art, the problems that a broadband light radiation device is high in component requirement function or complex in structure and the like can be effectively solved.
Description
Technical Field
The invention belongs to the technical field of broadband light radiation control, and particularly relates to a device and a method for generating broadband light radiation based on a chirped nonlinear crystal.
Background
The space coherent ultra-wideband light source has wide application in the fields of scientific research, component measurement, material component detection, medical diagnosis, imaging and the like. For example, a spatially coherent broadband mid-infrared light source may be used to enable high sensitivity identification and quantitative detection of multi-component gases.
The mid-infrared light source based on the optical parametric oscillator is the most commonly used broadband light source which has both correlation and high spectral brightness at present. There are three main methods currently in use for optical parametric oscillators to generate broadband optical radiation in the mid-infrared in excess of 1000 nm. One is that a short second-order nonlinear crystal is pumped by a pumping source with the pulse width of only tens of femtoseconds, the method has higher requirement on the pumping source, and the working pulse width is only tens of femtoseconds, so the stability is difficult to control [ S.C. Kumar et al, "Few-cycle, broadband, mid-isolated optical parameter oscillator pumped by a 20-fs Ti: sapphire Laser," Laser Photonics Rev.8, L86(2014) ]; secondly, it works in a degenerate mode, in which the pump wavelength must be half the generated wavelength, so that the mode is limited to a few bands [ n.leindecker et al, "Broadband generated OPO for mid-not-contaminated frequency comb generation," opt.express 19,6296(2011) ]; third, the Chirped pulse optical parametric oscillator, however, this mode requires the introduction of an additional third-order nonlinear crystal as an intracavity element and an additional focusing cavity, and its structure is relatively complex [ Pei Liu and zhaoweii Zhang, "Chirped-pulse optical parametric oscillators," opt. Lett.43,4735-4738(2018) ].
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, an object of the present invention is to provide an apparatus and a method for generating broadband optical radiation based on chirped nonlinear crystal, wherein by improving various components of the apparatus and their working relationship, etc., and especially by using a quasi-phase matching second-order nonlinear crystal designed based on chirped period, the problems of high requirements on components, complex structure, etc. of a broadband optical radiation apparatus can be effectively solved compared with the prior art. According to the invention, by setting a quasi-phase matching second-order nonlinear crystal with a chirp period design in a synchronous pump optical parametric oscillator, gain regions of signals with different wavelengths are spatially separated, and chirp pulses with broadband spectrums can be generated; broadband optical radiation can be achieved even under the restriction of the signal pulses by the pump pulses of the synchronous pump optical parametric oscillator.
To achieve the above object, according to one aspect of the present invention, there is provided an apparatus for generating a broadband optical radiation based on a chirped nonlinear crystal, characterized in that the apparatus is a synchronous pump optical parametric oscillator of a quasi-phase-matched second-order nonlinear crystal designed based on a chirp period so as to be able to generate a broadband optical radiation; the bandwidth of the broadband light radiation is not lower than the spectral bandwidth of the pump light;
the synchronous pump optical parametric oscillator adopts a quasi-phase matching second-order nonlinear crystal with a chirp period design as a material for carrying out nonlinear frequency conversion in the synchronous pump optical parametric oscillator; the crystal has different period lengths at different positions, and different periods correspond to phase matching at different wavelengths; when pump light generated by a pump source in the synchronous pump light parametric oscillator passes through a quasi-phase matching second-order nonlinear crystal designed by the chirp period, different signal wavelengths are generated at different positions of the crystal;
cavity mirrors are further respectively arranged at two ends of the quasi-phase matching second-order nonlinear crystal designed according to the chirp period so that a resonant cavity can be established, and the cavity mirrors are further used for providing positive feedback to signal light; the resonant cavity is provided with a dispersion functional element, the dispersion functional element is used for compensating dispersion introduced by the quasi-phase matching second-order nonlinear crystal of the chirp period design and can provide dispersion to reduce net dispersion in the resonant cavity; the dispersion function element is at least one of the cavity mirror and an intracavity dispersion management element independently arranged in the cavity;
the synchronous pump optical parametric oscillator comprises a quasi-phase matching second-order nonlinear crystal designed by the chirp period and the dispersion functional element, and can generate the broadband optical radiation under the pumping of a pumping source.
As a further preferred aspect of the present invention, for the quasi-phase-matching second-order nonlinear crystal designed with the chirp period, because different periods of the crystal correspond to phase matching at different wavelengths, specifically, the period lengths corresponding to the crystal are respectively calculated according to the shortest wavelength and the longest wavelength of broadband light radiation required to be generated and are used as the start period and the end period of the crystal;
preferably, the start period and the end period both satisfy:
Λ＝1/(np/λp-ns/λs-ni/λi)；
wherein Λ represents the start period or the end period, np、nsAnd niRespectively representing the refractive indices of the pump, signal and idler light, lambdap、λsAnd λiRespectively representing the wavelengths, λ, of the pump, signal and idler lightsTaking the value as the shortest wavelength or the longest wavelength of broadband light radiation required to be generated; under the pumping of a pumping source, the synchronous pump light parametric oscillator generates broadband idler frequency light simultaneously besides generating the broadband optical radiation as signal light through the combined action of the quasi-phase matching second-order nonlinear crystal designed by the chirp period and the dispersion functional element.
As a further preferred aspect of the present invention, for the quasi-phase-matching second-order nonlinear crystal designed with the chirp period, the quasi-phase-matching period from the start period to the end period of the crystal increases linearly or decreases linearly along the crystal, or increases nonlinearly or decreases nonlinearly.
As a further preferred aspect of the present invention, the broadband optical radiation is chirped pulses;
the chirped pulse has a pulse width not less than L (beta)pump-βsignal) Wherein L is the length of the quasi-phase-matching second-order nonlinear crystal designed according to the chirp period, betapumpAnd betasignalThe pulse width of the pump light is not less than the pulse width of the chirp pulse, and accordingly, the group velocity of the pump light and the group velocity of the signal light corresponding to the initial period in the second-order nonlinear crystal are inverse.
As a further preferred aspect of the present invention, when the dispersion function element includes an intracavity independently provided intracavity dispersion management element, the intracavity independently provided intracavity dispersion management element is a prism pair, a grating pair or a chirped mirror.
As a further preferred aspect of the present invention, the broadband optical radiation is a chirped pulse, and the chirped pulse is further pulse-compressed by an extra-cavity dispersion management element, where the extra-cavity dispersion management element is a prism pair, a grating pair, or a chirped mirror.
According to another aspect of the present invention, the present invention provides a method for generating broadband optical radiation by using the above apparatus, wherein the method is characterized in that the apparatus for generating broadband optical radiation by using the chirp nonlinear crystal is used, and the pump light generated by the pump source is subjected to the combined action of the quasi-phase matching second-order nonlinear crystal designed by chirp period and the dispersion function element to generate broadband optical radiation; the bandwidth of the broadband light radiation is not lower than the spectral bandwidth of the pump light.
Compared with the prior art, the technical scheme of the invention has the advantages that the quasi-phase matching second-order nonlinear crystal designed by the chirp period is used as a functional component for nonlinear frequency conversion (the period lengths at different positions in the crystal are different, and different periods correspond to phase matching at different wavelengths), when pump light generated by a pump source in the synchronous pump light parametric oscillator passes through the quasi-phase matching second-order nonlinear crystal designed by the chirp period, different signal wavelengths are generated at different positions of the crystal), and the broadband light radiation with the bandwidth not lower than the spectral bandwidth of the pump light can be generated by utilizing the resonant cavity dispersion functional element, particularly the broadband light radiation with the bandwidth more than 1000nm can be generated in a middle infrared band. By using the device and the corresponding method, the bandwidth range can be controlled by the chirp design of the second-order nonlinear crystal, and the broadband light radiation can be realized in any wave band for implementing quasi-phase matching. And the dispersion management element outside the cavity can be further utilized and used for compressing the chirped pulse output by the oscillator to obtain the ultrashort pulse.
The broadband light radiation generated by the device and the method is chirp pulse, and the requirement on the synchronism is low, so the stability is good; because the quasi-phase matching second-order nonlinear crystal adopting the chirp design can realize high gain and large bandwidth at the same time, the efficiency is high and the threshold value is low.
The cavity mirrors respectively arranged at two ends of the quasi-phase matching second-order nonlinear crystal designed in the chirp period can be used for providing positive feedback to signal light and providing certain dispersion so as to reduce net dispersion in the resonant cavity (at the moment, the cavity mirrors are used as dispersion functional elements). Further, the net dispersion in the oscillator cavity should be as close to zero as possible to ensure the bandwidth of the broadband optical radiation. If the chromatic dispersion provided by the cavity mirror can not compensate the chromatic dispersion introduced by the quasi-phase matching second-order nonlinear crystal with the chirp period design, the invention can additionally and independently set an intracavity dispersion management element (such as a prism pair, a grating pair and the like) so that the net dispersion in the resonant cavity is close to zero (at the moment, the cavity mirror and the intracavity dispersion management element are simultaneously used as dispersion functional elements); of course, the cavity mirror may also be completely non-dispersive (providing no dispersion), with the net dispersion within the cavity being close to zero by arranging the intra-cavity dispersion management element (in which case the intra-cavity dispersion management element will act solely as a dispersive function).
The invention can obtain the chirped pulse optical radiation with certain pulse width but far wider spectral bandwidth than the pumping bandwidth in the optical parametric oscillator under the limit of the pumping pulse width to the oscillation pulse width by using the quasi-phase matching second-order nonlinear crystal with chirped design. The mechanism of generation of broadband signal light in a single-resonance optical parametric oscillator is as follows: the quasi-phase matching second-order nonlinear crystal designed by the chirp period has different period lengths at different positions and different corresponding phase matching wavelengths, and when a pump pulse passes through the quasi-phase matching second-order nonlinear crystal, different signal wavelengths can be generated at different positions of the crystal; because the generated signal light is separated from the pump light in the crystal, the wavelength of the signal generated firstly is not overlapped with that of the signal generated later in space, and the generated signal pulse is a chirp pulse; and when the total net dispersion of the oscillator is close to zero, the generated chirped pulse can be continuously circulated in the oscillator to maintain stability, so that broadband light radiation is realized.
The invention designs the quasi-phase matching second-order nonlinear crystal with the chirp period, and simultaneously controls the net dispersion of the oscillator to be near zero, thereby realizing the generation of chirp pulses with broadband spectrum.
Compared with the three main methods in the prior art that an optical parametric oscillator is used for generating broadband light radiation with the middle infrared of more than 1000nm, the first method in the prior art adopts a pumping source with the pulse width of only tens of femtoseconds to pump a short second-order nonlinear crystal, the method has higher requirement on the pumping source, and the stability is difficult to control because the working pulse width is only tens of femtoseconds; the second method in the prior art is to work in a degenerate mode, in which the pump wavelength is half of the generated wavelength, so that the mode is limited to a few bands, and the invention has no obvious wavelength limitation and can be applied to all bands capable of adopting quasi-phase matching crystals; the third method in the prior art is a chirped pulse photoparametric oscillator, however, in the mode, an additional third-order nonlinear crystal needs to be introduced as an intracavity element and an additional focusing cavity, the structure is relatively complex, only one crystal needs to be adopted, and the structure of a cavity is greatly simplified.
The broadband optical radiation generated by the oscillator is a chirped pulse, and the pulse width of the chirped pulse is approximately equal to the group velocity mismatch of the pump wavelength and the phase matching wavelength corresponding to the starting period of the second-order nonlinear crystal in the second-order nonlinear crystal. The pulse width of the pump light in the invention is not less than that of the chirp pulse.
In addition, the chirped pulse can realize pulse compression through dispersion management outside the cavity, thereby obtaining an ultrashort pulse. For dispersion management components outside the cavity, such as a prism pair, a grating pair, a chirped mirror and the like, the conventional method of pulse compression can be used for reference, for example, the pulse width after compression is measured by continuously changing the interval of the prism pair, the grating pair or the number of the chirped mirrors, and finally ultrashort pulses close to the conversion limit are obtained; in this way, the chirped pulses may be pulse compressed by a dispersion management element outside the cavity to obtain ultrashort pulses corresponding to the near-conversion limit of the generated broadband spectrum.
In summary, it is obvious that the device and method for generating broadband optical radiation by using the synchronous pump optical parametric oscillator based on the quasi-phase matching second-order nonlinear crystal designed based on the chirp period in the present invention can generate broadband optical radiation by using the synchronous pump optical parametric oscillator, and the method is simple and effective.
Drawings
Fig. 1 is a schematic structural diagram of a synchronous pump optical parametric oscillator of a quasi-phase matching second-order nonlinear crystal designed based on a linear chirp period in embodiment 1 of the present invention.
Fig. 2 is a polarization period distribution diagram of a quasi-phase-matching second-order nonlinear crystal of the linear chirp period design used in embodiment 1 of the present invention.
FIG. 3 is a spectral plot of broadband optical radiation generated in example 1 of the present invention.
Fig. 4 is a time-domain distribution diagram of the chirped pulse generated in embodiment 1 of the present invention and the ultrashort pulse obtained after the extra-cavity dispersion management.
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.
The invention generally relates to a method for generating chirp pulses with broadband spectrum by designing a quasi-phase matching second-order nonlinear crystal with a chirp period and controlling the net dispersion of an oscillator to be near zero. The device for generating the broadband light radiation based on the chirped nonlinear crystal can be carried out according to the following steps when specific parameters of each element are set or designed:
(1) according to the central wavelength of the required broadband light radiation, selecting pump light with the wavelength less than the central wavelength and a transparent quasi-phase matching second-order nonlinear crystal capable of realizing phase matching on the pump light, the signal light and the idler frequency light. For example, if the center wavelength is 1.5 μm, 1 μm may be selected as the pump light while the periodically poled lithium niobate crystal is selected as the quasi-phase-matched second order nonlinear crystal.
(2) According to the required widthWith the longest and shortest wavelengths of the light radiation, by Λ ═ 1/(n)p/λp-ns/λs-ni/λi) (where Λ represents the polarization period corresponding to the quasi-phase matching, n represents the refractive index, λ represents the wavelength, and subscripts p, s, i represent the pump light, the signal light, and the idler light, respectively) determining the initial and final polarization period lengths of the corresponding quasi-phase matching second-order nonlinear crystal; then determining the quasi-phase matching period length between the starting period and the ending period of the crystal according to a certain rule (linearly increasing or decreasing, or nonlinearly increasing or decreasing, but the slope of the sign is the same as that of the starting period and the ending period); the total length of the crystal can be determined according to actual conditions, and the shorter the crystal, the higher the required pump source power and the shorter the pulse width are, and the total length can be designed through numerical calculation.
(3) The width of the pump pulse used should correspond to the length of the second order nonlinear crystal determined in step (2) and the wavelength for which the start period is designed to be phase-matched, i.e. the pump pulse width should be as close as possible to the group velocity mismatch of the wavelength for which the end period is phase-matched and the pump wavelength.
(4) The total dispersion in the oscillator other than the quasi-phase-matched second-order nonlinear crystal should compensate the dispersion of the quasi-phase-matched second-order nonlinear crystal as much as possible.
In the oscillator, cavity mirrors are respectively arranged at two ends of a second-order nonlinear crystal to form a resonant cavity; the cavity mirror can provide certain dispersion to reduce the net dispersion in the resonant cavity, so that the net dispersion in the resonant cavity is close to zero, and if the dispersion provided by the cavity mirror cannot compensate the dispersion introduced by the quasi-phase matching second-order nonlinear crystal with the chirp period design, the invention can further arrange a dispersion management element (such as a prism pair, a grating pair, a chirp mirror and the like; not shown in figure 1) in the cavity, so that the net dispersion in the resonant cavity is close to zero.
Of course, the cavity mirror may also be completely non-dispersive (i.e. not providing any dispersion), with the net dispersion within the cavity being close to zero by arranging the intra-cavity dispersion management element (in which case the intra-cavity dispersion management element will act solely as a dispersive function).
Further, the method can comprise the following steps:
(5) the generated chirped pulse can realize pulse compression through dispersion management outside the cavity, so that an ultrashort pulse is obtained. For example, the conventional method of pulse compression can be used for reference, such as measuring the pulse width after compression by continuously changing the prism pair, the grating pair interval or the number of chirped mirrors, and finally obtaining the ultra-short pulse close to the conversion limit; in this way, the chirped pulses may be pulse compressed by a dispersion management element outside the cavity to obtain ultrashort pulses corresponding to the near-conversion limit of the generated broadband spectrum.
Example 1:
FIG. 1 is a schematic diagram of the process of the present invention. The invention relates to a quasi-phase matching second-order nonlinear crystal and a cavity mirror with chirp period design in a resonant cavity of an optical parametric oscillator. The quasi-phase matching second-order nonlinear crystal designed by the chirp period provides gains for signal light with different wavelengths at different crystal positions, so that the signal light can oscillate in a cavity; the cavity mirror is used for providing positive feedback and providing certain dispersion, and if the dispersion provided by the cavity mirror cannot compensate the dispersion introduced by the crystal, the dispersion can also be compensated by other dispersion management elements, such as a prism pair, a grating pair and the like, so that the net dispersion in the cavity is close to zero.
The cavity mirror can provide certain dispersion, and the dispersion introduced by the cavity mirror can be optimized through calculation due to the fact that the reflection of the coated film of the cavity mirror is accompanied with the dispersion, so that the compensation of crystal dispersion can be achieved.
The following is a detailed description of a numerical simulation example.
The selected quasi-phase matching second-order nonlinear crystal is a periodically polarized lithium niobate crystal. The pump light comes from the mode-locked fiber laser and amplifier system, the center wavelength is 1058nm, the pulse width is about 230fs, and the repetition frequency is 90 MHz. The crystal length was about 2mm, its central polarization period was 28.11 μm, and the chirp slope was 2 × 107The polarization periods are specifically distributed as shown in fig. 2. When the pumping power is 3W and the net second-order dispersion in the cavity is 180fs2The resulting spectra of the signal and idler are shown in fig. 3. At this time, the signalThe-30 dB bandwidth of the optical spectrum is 310nm, and the-30 dB bandwidth of the idler frequency optical spectrum is 1982 nm. Because the chirp characteristics of the generated chirp pulses are caused by the quasi-phase matching second-order nonlinear crystal of the chirp design, pulse compression can be realized through dispersion management outside the cavity, and the chirp pulses with the original full width at half maximum of 344 femtoseconds are compressed into ultrashort pulses of only 28 femtoseconds by using a 132mm fused quartz material in simulation.
The invention adopts the quasi-phase matching second-order nonlinear crystal designed by the chirp period in the optical parametric oscillator, controls the net dispersion in the cavity to be close to zero, can realize the output of the chirp pulse with a wide instantaneous bandwidth spectrum, can realize ultrashort pulse through dispersion management outside the cavity, and has important potential application value.
In addition to the quasi-phase-matching second-order nonlinear crystal designed according to the linear chirp period adopted in embodiment 1, the synchronous pump optical parametric oscillator may also adopt a quasi-phase-matching second-order nonlinear crystal designed according to a nonlinear chirp period; in this case, other elements in the synchronous pump optical parametric oscillator may be similarly arranged.
The invention forms the resonant cavity by respectively arranging the cavity mirrors at the two ends of the second-order nonlinear crystal, the specific structure of the resonant cavity can be designed by referring to the resonant cavity in the prior art, and the resonant cavity can be in a diversified structure. The extra dispersion management element can be divided into an intracavity dispersion management element and an extracavity dispersion management element, wherein the intracavity dispersion management element is used for compensating dispersion introduced by the crystal so as to play a role in controlling net dispersion in the cavity, and the extracavity dispersion management element is used for compressing chirped pulses output by the oscillator so as to obtain ultrashort pulses; in addition, the positions of the intracavity dispersion management element and the extra-cavity dispersion management element are different, but the specific elements can be the same and can comprise a prism pair, a grating pair or a chirped mirror.
The quasi-phase matching second-order nonlinear crystal designed by the chirp period (such as the quasi-phase matching second-order nonlinear crystal designed by a linear or nonlinear chirp period) can be prepared by referring to the prior art; the chirp related characteristic parameters can be regulated and controlled by referring to the prior art; for example, reference may be made to G.D. Miller, "periodic polar nitrile: modifying, hybridization, and nonlinear-optical performance," Ph.D. thesis (Stanford University, 1998).
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.
Claims (7)
1. An apparatus for generating broadband optical radiation based on a chirped nonlinear crystal is characterized in that the apparatus is a synchronous pump optical parametric oscillator of a quasi-phase matching second-order nonlinear crystal designed based on a chirped period so as to generate broadband optical radiation; the bandwidth of the broadband light radiation is not lower than the spectral bandwidth of the pump light;
the synchronous pump optical parametric oscillator adopts a quasi-phase matching second-order nonlinear crystal with a chirp period design as a material for carrying out nonlinear frequency conversion in the synchronous pump optical parametric oscillator; the crystal has different period lengths at different positions, and different periods correspond to phase matching at different wavelengths; when pump light generated by a pump source in the synchronous pump light parametric oscillator passes through a quasi-phase matching second-order nonlinear crystal designed by the chirp period, different signal wavelengths are generated at different positions of the crystal; because the generated signal light has a walk-off effect with the pump light in the crystal, the wavelength of the signal generated firstly is not overlapped with that of the signal generated later in space, and the generated signal pulse is a chirp pulse;
cavity mirrors are further respectively arranged at two ends of the quasi-phase matching second-order nonlinear crystal designed according to the chirp period so that a resonant cavity can be established, and the cavity mirrors are further used for providing positive feedback to signal light; the resonant cavity is provided with a dispersion functional element, the dispersion functional element is used for compensating dispersion introduced by the quasi-phase matching second-order nonlinear crystal of the chirp period design and can provide dispersion to reduce net dispersion in the resonant cavity; the dispersion function element is at least one of the cavity mirror and an intracavity dispersion management element independently arranged in the cavity;
the synchronous pump optical parametric oscillator comprises a quasi-phase matching second-order nonlinear crystal designed by the chirp period and the dispersion functional element, and can generate the broadband optical radiation under the pumping of a pumping source.
2. The apparatus for generating broadband optical radiation based on chirped nonlinear crystal according to claim 1, wherein for the quasi-phase-matched second-order nonlinear crystal designed based on the chirped period, due to the fact that different periods of the crystal correspond to phase matching at different wavelengths, the period lengths corresponding to the crystal are respectively calculated according to the shortest wavelength and the longest wavelength of the broadband optical radiation to be generated and are used as the starting period and the ending period of the crystal;
the start period and the end period both satisfy:
Λ＝1/(np/λp-ns/λs-ni/λi)；
wherein Λ represents the start period or the end period, np、nsAnd niRespectively representing the refractive indices of the pump, signal and idler light, lambdap、λsAnd λiRespectively representing the wavelengths, λ, of the pump, signal and idler lightsTaking the value as the shortest wavelength or the longest wavelength of broadband light radiation required to be generated; under the pumping of a pumping source, the synchronous pump light parametric oscillator generates broadband idler frequency light simultaneously besides generating the broadband optical radiation as signal light through the combined action of the quasi-phase matching second-order nonlinear crystal designed by the chirp period and the dispersion functional element.
3. The apparatus for generating broadband optical radiation based on chirped nonlinear crystals according to claim 2, wherein for the chirped period designed quasi-phase-matched second-order nonlinear crystal, the quasi-phase-matching period from the start period to the end period of the crystal is linearly increased or linearly decreased along the crystal, or is non-linearly increased or non-linearly decreased.
4. The apparatus for generating broadband optical radiation based on a chirped nonlinear crystal according to claim 3, wherein the broadband optical radiation is chirped pulses.
5. The apparatus for generating broadband optical radiation based on a chirped nonlinear crystal according to claim 1, wherein when the dispersion function element comprises an intracavity independently disposed intracavity dispersion management element, the intracavity independently disposed intracavity dispersion management element is a prism pair, a grating pair, or a chirped mirror.
6. The apparatus for generating broadband optical radiation based on a chirped nonlinear crystal according to claim 1, wherein the broadband optical radiation is chirped pulses, and the chirped pulses are further pulse compressed by an extra-cavity dispersion management element, the extra-cavity dispersion management element being a prism pair, a grating pair, or a chirped mirror.
7. A method for generating broadband optical radiation by using the device according to any one of claims 1 to 6, wherein the device for generating broadband optical radiation based on the chirped nonlinear crystal according to any one of claims 1 to 6 is used, and the pump light generated by the pump source, the quasi-phase matching second-order nonlinear crystal designed by the chirped period and the dispersion function element are used together to generate broadband optical radiation; the bandwidth of the broadband light radiation is not lower than the spectral bandwidth of the pump light.
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