CN110739603B - Medium-long wave infrared femtosecond pulse generating and amplifying device - Google Patents
Medium-long wave infrared femtosecond pulse generating and amplifying device Download PDFInfo
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- CN110739603B CN110739603B CN201910944967.8A CN201910944967A CN110739603B CN 110739603 B CN110739603 B CN 110739603B CN 201910944967 A CN201910944967 A CN 201910944967A CN 110739603 B CN110739603 B CN 110739603B
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Abstract
The invention discloses a medium-long wave infrared femtosecond pulse generating and amplifying device. The device amplifies near-infrared ultrashort pulse laser through double chirped pulse optical parameters to obtain narrow-band seed light with micro-focus level, and then the narrow-band seed light is directly injected into a holmium-doped crystal through amplifier for energy promotion and is used as pump light; meanwhile, the same near-infrared ultrashort pulse is used for splitting beams, medium-long wave broadband signal light is obtained through optical parametric conversion, and finally the medium-long wave broadband signal light and the pump light are amplified through an optical parametric process, so that amplified medium-long wave infrared femtosecond pulses are obtained, and a reliable driving source is provided for attosecond pulse generation. The device has the advantages of high conversion efficiency and high synchronization precision, and can greatly improve the pulse energy and the work repetition frequency of the medium-long wave infrared femtosecond pulse.
Description
Technical Field
The invention belongs to the technical field of ultrashort pulse generation and amplification, and relates to a medium-long wave infrared femtosecond pulse generation and amplification device.
Background
Attosecond (1as ═ 10)-18s) is the shortest time scale currently held by human beings, which advances human understanding of the microstructure of a micro-substance from the level of atoms, molecules and lattices to the level of internal electrons of atoms. It can clearly distinguish the time scale of electron and atomic nucleus motion, and is an important means for measuring and controlling the electron dynamics process. In 2001, f.kraussz, mappo, germany, produced isolated attosecond pulses of pulse width 650as for the first time in the laboratory. Since the birth of attosecond impulse, how to generate wider supercontinuum and further compress the spectrum to obtain shorter attosecond impulse has been the most central problem in attosecond science. The attosecond pulse with narrower pulse width and higher photon energy can be used for the electron dynamics research of the inner shell of the atom and becomes the most important basic of the disciplines of revealing atom/molecule physics, condensed state physics, chemistry and the likeA powerful tool for the process. For example: the electron action and movement of the atomic inner shell layer and the manipulation of the electron movement in the atom by the photoelectric field force are explored in the basic physical field.
According to the attosecond generation theory, the cut-off wavelength of the higher harmonic generation is proportional to the square of the driving laser wavelength, i.e.
The long wave drive source will obtain a wider XUV/soft X-ray spectrum, enabling the acquisition of narrower attosecond pulses. Therefore, the research on the longer wavelength attosecond driving source technology is becoming an important development direction of attosecond pulse light source and its application field. In addition, longer wavelength infrared pulsed lasers have important applications in many fields, such as: the volatile matter in the molecular fingerprint area can be quickly identified by adopting a mid-infrared light source without scanning; the vibration spectrum of the infrared molecule fingerprint area with the size of 2-25 mu m can provide the composition and structure information of molecules, so that the method is applied to the fields of safety, environment, biology and medicine.
In the light wave range of the medium-long wave infrared femtosecond pulse, a broadband and high-energy pulse laser gain medium is lacked. Moreover, if near-infrared ultrashort pulses are used for directly pumping the amplification of medium-long wave infrared, the conversion efficiency is very low. In particular, because of the limitation of the single pulse energy or repetition frequency of the near-infrared ultrashort pulse itself, the energy and power of the finally obtained medium-wavelength infrared pulse are low, and the requirements of the application such as attosecond pulse generation cannot be met.
Disclosure of Invention
The invention aims to: in order to generate higher photon energy, attosecond pulse with narrower pulse width and related application of medium-long wave infrared femtosecond pulse, a medium-long wave infrared femtosecond pulse generating and amplifying system is provided, and the system can remarkably improve the energy and power of the medium-long wave infrared femtosecond pulse, thereby providing a reliable driving source for attosecond pulse generation.
The basic principle of the invention is as follows:
near-infrared ultrashort pulse laser with single pulse energy above the milli-focus level is subjected to parametric amplification through double chirped pulse light to obtain micro-focus narrow-bandwidth 2.05 mu m seed light, and then the seed light is directly injected into a holmium-doped crystal through amplifier to be subjected to energy boosting and is used as pump light. Meanwhile, the beam splitting light of the same front-stage near-infrared ultrashort pulse is adopted to obtain medium-long wave broadband signal light with the wavelength larger than 2.5 microns through optical parametric conversion, and the broadband signal light is finally amplified through the optical parametric process of high-energy pulse pump light with the wavelength of 2.05 microns, so that the purposes of generating and amplifying medium-long wave infrared femtosecond pulses are achieved, and a reliable driving source is provided for attosecond pulse generation.
The invention adopts the following specific technical scheme for solving the technical problems:
the invention provides a medium-long wave infrared femtosecond pulse generating and amplifying device, which comprises a near-infrared ultrashort pulse laser source, a first beam splitter, a first reflector, a seed light generating and amplifying unit, a holmium-doped laser amplifying unit, a medium-long wave broadband signal light generating unit, a second reflector and a double-chirp amplifying unit, wherein the near-infrared ultrashort pulse laser source is connected with the first beam splitter;
the emergent light of the near-infrared ultrashort pulse laser light source is split into two paths after passing through the first beam splitter, one path of light beam enters the seed light generating and amplifying unit through the first reflector to generate narrow-band seed light, and then the narrow-band seed light enters the holmium-doped laser amplifying unit to become pump light; the other light path generates medium-long wave broadband signal light through a medium-long wave broadband signal light generating unit;
after the pumping light is reflected by the second reflector, the medium-long wave broadband signal light and the medium-long wave broadband signal light enter the double-chirp amplification unit together to generate medium-long wave infrared femtosecond pulses with energy reaching more than a millifocus level;
the working wavelength of the near-infrared ultrashort pulse laser source is 790nm or 1 μm, and the single pulse energy of the near-infrared ultrashort pulse laser source is more than the millijoule level and can reach dozens or even hundreds of millijoules;
the wavelength of the narrow-band seed light is 2.05 mu m, and the single pulse energy of the narrow-band seed light is greater than the micro-focus level;
the wavelength of the pump light is 2.05 mu m, the single pulse energy of the pump light is more than tens of times of that of narrow-band seed light, and the pump light can reach hundred millijoules;
the wavelength of the medium-long wave broadband signal light is more than 2.5 mu m, and the single pulse energy only needs a nano-focus level.
Specifically, the seed light generating and amplifying unit includes a second beam splitter, a third mirror, a first focusing mirror, a first spectrally spreading material, a first collimating mirror, a first dispersive element, a first difference frequency crystal, a filter, a second difference frequency crystal, a second dispersive element, a third beam splitter, a first mirror group, a fourth mirror, and a second mirror group;
an incident beam is divided into two beams of light by a second beam splitter, wherein a third reflector, a first focusing mirror, a first spectrum broadening material, a first collimating mirror, a first dispersion element, a first difference frequency crystal, a filter and a second difference frequency crystal are sequentially arranged on the light path of one beam of light;
another beam of light is divided into two beams of light again through a third beam splitter, and one beam of light is injected into the first difference frequency crystal after sequentially passing through the second dispersive element and the first reflector group;
and the other beam of light is injected into the second difference frequency crystal after passing through the third dispersive element, the fourth reflector and the second reflector group in sequence, so that narrow-band seed light is generated.
Specifically, the holmium-doped laser amplification unit is a one-pass holmium-doped laser amplifier, a two-pass holmium-doped laser amplifier, a multi-pass holmium-doped laser amplifier, or a combination amplifier of one-pass, two-pass and multi-pass.
Specifically, the medium-wavelength broadband signal light generating unit includes a fourth beam splitter, a fifth mirror, a second focusing mirror, a second spectral broadening material, a second collimating mirror, a fourth dispersive element, a third difference frequency crystal, a fifth dispersive element, and a third mirror group;
an incident beam is divided into two beams of light through a fourth beam splitter, wherein a fifth reflector, a second focusing mirror, a second spectrum broadening material, a second collimating mirror, a fourth dispersive element and a third difference frequency crystal are sequentially arranged on the light path of one beam of light;
the other beam of light is incident to the third difference frequency crystal through the fifth dispersion element and the third reflector group in sequence, so that the medium-wavelength broadband signal light is generated.
Specifically, the double-chirped amplification unit comprises a sixth dispersion element, a fourth difference frequency crystal, a dispersion compensation device, a seventh dispersion element and a fourth mirror group;
a sixth dispersion element, a fourth difference frequency crystal and a dispersion compensation device are sequentially arranged on the light path of the medium-long wave broadband signal light;
the pumping light sequentially passes through the seventh dispersion element and the fourth reflector group and then is incident to the fourth difference frequency crystal, so that the intermediate-wavelength infrared femtosecond pulse is generated.
Specifically, the near-infrared ultrashort pulse laser source is a solid or fiber ultrashort pulse laser.
Specifically, the first difference frequency crystal, the second difference frequency crystal and the third difference frequency crystal are all made of barium metaborate (BBO), bismuth metaborate (BI BO) or Periodically Poled Lithium Niobate (PPLN), and the fourth difference frequency crystal is made of phosphorus germanium zinc crystal (ZGP).
Specifically, the first dispersion element, the second dispersion element, the third dispersion element, the fourth dispersion element, and the fifth dispersion element are block materials, grating pairs, prism pairs, volume bragg gratings, or chirped mirrors.
Specifically, the sixth dispersive element and the seventh dispersive element are acousto-optic programmable logic devices (AOPDFs).
Specifically, the first spectrum broadening material is sapphire (Al)2O3) (ii) a The second spectrum broadening material adopts potassium titanyl arsenate (KTA) crystal or sapphire.
The invention has the beneficial effects that:
1. the invention generally adopts an optical parameter technology to obtain narrow-band 2.05 mu m seed light above micro-focus level, and the seed light is directly injected into holmium-doped through amplification to improve pulse energy for pumping medium-long wave infrared femtosecond pulse amplification. The method has the advantages of high conversion efficiency and high synchronization precision, and can greatly improve the pulse energy and the work repetition frequency of the medium-long wave infrared femtosecond pulse, thereby providing a reliable driving source for attosecond pulse generation and providing a powerful support for the application in the fields of biomedicine, strong field physics, terahertz and the like.
2. In the invention, the 2.05 μm seed light is generated, and the 2.05 μm seed light with narrow bandwidth and micro-focus magnitude is obtained by adopting a way of adjusting the dispersion amount by using a double-chirp optical parametric amplification technology. The narrow spectral bandwidth can well match the emission spectrum width of the holmium-doped crystal; and pulse energy of micro-focus magnitude can be directly amplified through holmium doping, so that high-precision synchronization of subsequent amplification is guaranteed.
3. The holmium-doped crystal direct amplification method has the advantages of energy improvement: the upper energy level of the holmium-doped crystal has long service life, 1.94 mu m of thulium-doped continuous laser pumping can be directly adopted, and the conversion efficiency is high; and the repetition frequency of the amplification of the holmium-doped crystal can be from kHz to MHz, so that high repetition frequency can be realized.
4. In the invention, 2.05 mu m pulse laser is used as pump light for amplifying the medium-long wave femtosecond pulse, and compared with the existing 790nm or 1 mu m wavelength ultrashort pulse, the conversion efficiency from the pump light to medium-long wave infrared is higher.
Drawings
FIG. 1 is a functional block diagram of the present invention;
FIG. 2 is a schematic diagram of a seed light generating and amplifying unit;
fig. 3 is a schematic structural diagram of a one-pass holmium-doped laser amplifier;
FIG. 4 is a schematic structural diagram of a two-way holmium-doped laser amplifier;
FIG. 5 is a schematic structural diagram of a multipass holmium-doped laser amplifier;
FIG. 6 is a schematic structural diagram of a medium-and-long-wavelength broadband signal light generating unit;
fig. 7 is a schematic structural diagram of a dual chirp amplification unit.
The reference numbers are as follows:
1-near infrared ultrashort pulse laser light source, 2-first beam splitter, 3-first reflector, 4-seed light generating and amplifying unit, 5-holmium-doped laser amplifying unit, 6-medium-long wave broadband signal light generating unit, 7-second reflector, 8-double-chirp amplifying unit, 10-second beam splitter, 11-third reflector, 12-first focusing mirror, 13-first spectrum broadening material, 14-first collimating mirror, 15-first dispersion element, 16-first difference frequency crystal, 17-filter, 18-second difference frequency crystal, 19-second dispersion element, 20-third dispersion element, 21-third beam splitter, 22-first reflector group, 23-fourth reflector, 24-second reflector group, 25-fourth beam splitter, 26-fifth reflector, 27-second focusing mirror, 28-second spectrum broadening material, 29-second collimating mirror, 30-fourth dispersion element, 31-third difference frequency crystal, 32-fifth dispersion element, 33-third reflector set, 34-sixth dispersion element, 35-fourth difference frequency crystal, 36-dispersion compensation device, 37-seventh dispersion element and 38-fourth reflector set.
01-chirp pulse stretcher, 02-optical isolator, 03-holmium-doped crystal, 04-fiber collimator and 05-pumping source; 06-chirped pulse compressor, 07-dichroic beam splitter; 08-sixth mirror, 09-polarization beam splitter, 010-quarter wave plate, 011-0o mirror and 012-seventh mirror.
M1, M2, M3, M4, M5, M6, M7, M8, M9, M10, M11, M12, M13-mirror.
Detailed Description
To make the objects, advantages and features of the present invention more apparent, a device for generating and amplifying mid-and-long-wavelength infrared femtosecond pulses according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It should be noted that: the drawings are in simplified form and are not to precise scale, the intention being solely for the convenience and clarity of illustrating embodiments of the invention; second, the structures shown in the drawings are often part of actual structures.
In order to realize the attosecond driving source in the middle infrared band, the generation and amplification of the middle-long wave femtosecond pulse with stable carrier envelope phase are realized based on a near-infrared ultrashort pulse laser source and by combining technical means such as double chirp and holmium-doped laser amplification. The basic implementation principle of the medium-long wave femtosecond pulse generating and amplifying device is shown in figure 1: the device comprises a near-infrared ultrashort pulse laser light source 1, a first beam splitter 2, a first reflector 3, a seed light generating and amplifying unit 4, a holmium-doped laser amplifying unit 5, a medium-long wave broadband signal light generating unit 6, a second reflector 7 and a double-chirp amplifying unit 8;
a femtosecond pulse (the pulse wavelength is 790nm or 1 μm, and the single pulse energy is above the millijoule level) output by a near-infrared ultrashort pulse laser light source 1 is divided into two beams by a first beam splitter 2, the first beam enters a seed light generating and amplifying unit 4 after passing through a first reflector 3 to obtain narrow-band seed light (the narrow-band seed light wavelength is 2.05 μm, the single pulse energy is greater than the microjoule level), then the narrow-band seed light enters a holmium-doped laser amplifying unit 5 to be subjected to pulse energy promotion, and picosecond pulses of several millijoules and even hundreds of millijoules are output after amplification as post-stage amplified pump light, the pump light wavelength is 2.05 μm, and the single pulse energy is more than tens of times of the narrow-band seed light;
the second beam passes through a medium-long wave broadband signal light generating unit 6 to obtain medium-long wave infrared broadband signal light, the wavelength of the medium-long wave infrared broadband signal light is more than 2.5 mu m, and the single pulse energy of the medium-long wave infrared broadband signal light only needs a nano focus level; finally, after the pumping light is reflected by the second reflector 7, the medium-long wave broadband signal light and the medium-long wave broadband signal light enter the double-chirp amplification unit 8 together to amplify the required medium-long wave infrared femtosecond pulse.
Based on the foregoing description of the basic structure of the device, the specific structure and operation of each optical device in the device will now be described in detail:
near-infrared ultrashort pulse laser light source
The near-infrared ultrashort pulse laser source is used as a preceding stage light source, the single pulse energy of the near-infrared ultrashort pulse laser source is more than the milli-focus level, the wavelength of the near-infrared ultrashort pulse laser source is mainly 1 μm and 790nm, and in the specific implementation process, the near-infrared ultrashort pulse laser source can be any one of a titanium sapphire femtosecond amplifier, an ytterbium-doped solid picosecond/femtosecond amplifier, an ytterbium-doped optical fiber picosecond/femtosecond amplifier or a neodymium-doped picosecond/femtosecond laser.
Seed light generating and amplifying unit
As shown in fig. 2, the seed light generating and amplifying unit includes a second beam splitter 10, a third reflector 11, a first focusing mirror 12, a first spectrally broadening material 13, a first collimating mirror 14, a first dispersive element 15, a first difference frequency crystal 16, a long pass filter 17, a second difference frequency crystal 18, a second dispersive element 19, a third dispersive element 20, a third beam splitter 21, a first reflector group 22, a fourth reflector 23, and a second reflector group 24;
an incident beam is divided into two beams of light by a second beam splitter 10, wherein a third reflector 11, a first focusing mirror 12, a first spectrum broadening material 13, a first collimating mirror 14, a first dispersive element 15, a first difference frequency crystal 16, a long-pass filter 17 and a second difference frequency crystal 18 are sequentially arranged on the light path of one beam of light;
another beam of light is divided into two beams of light again by the third beam splitter 21, and one beam of light is injected into the first difference frequency crystal 16 after passing through the second dispersive element 19 and the first reflector group 22 in sequence;
the other beam of light is injected into the second difference frequency crystal 18 after passing through the third dispersive element 20, the fourth reflecting mirror 23 and the second reflecting mirror group 24 in sequence, thereby generating narrow-band seed light.
The working principle is as follows: the femtosecond pulse output by the near-infrared ultrashort pulse laser source is split again by the second beam splitter 10, wherein one beam is focused into the first spectrum broadening material 13 (generally, a white gem stone) through the first focusing mirror 12 for spectrum broadening, and signal light with the wavelength of 1.29 μm is obtained. And then collimated by a first collimating mirror 14, and subjected to a first dispersive element 15 to obtain time domain broadening.
The other beam is split again by a third beam splitter 21, wherein one beam is adjusted in pulse width by a third dispersion element 20, is pumped to a first difference frequency crystal 16(BBO crystal) after being adjusted in delay by a first reflector group 22, obtains 2.05 μm pulse laser by utilizing the optical parametric process of 790nm and 1.29 μm pulses in the first difference frequency crystal 16, and enters the next stage of BBO double-chirped optical parametric amplification through a long pass filter 17. The pulse width of the other beam of 790nm fundamental frequency light is adjusted by the third dispersion element 20, and after the light is reflected by the fourth reflector 23, the second reflector group 24 is used for adjusting the time delay and then pumping the second difference frequency crystal 18, so that the amplification of 2.05 μm seed light is realized. Therefore, the seed light generating and amplifying unit adopts the principle of the double-chirp optical parametric amplifier, so that single-stage or multi-stage cascade use can be determined according to the actual amplification requirement in an experiment, and finally the single-pulse energy of the pulse laser with the output wavelength of 2.05 mu m reaches the micro-focus level.
Holmium-doped laser amplification unit
The holmium-doped laser amplification unit comprises any one of a one-pass holmium-doped laser amplifier, a two-pass holmium-doped laser amplifier, a multi-pass holmium-doped laser amplifier or a one-pass, two-pass and multi-pass combined amplifier. The holmium-doped crystal in the holmium-doped laser amplification unit is made of Ho-YLF crystal, Ho-YAG crystal or thulium-holmium co-doped crystal. The laser radiation energy level life of the holmium-doped crystal is about 10ms, so that pulse amplification with repetition frequency of more than hundreds of Hz can be realized by adopting continuous laser for pumping; and the same-band pump Ho/YLF crystal is carried out by adopting 1.94 mu m thulium-doped continuous laser, so that the optical conversion efficiency is very high.
The following brief descriptions of the one-way holmium-doped laser amplifier, the two-way holmium-doped laser amplifier or the multi-way holmium-doped laser amplifier are respectively made with reference to the accompanying drawings as follows:
(1) one-way holmium-doped laser amplifier
As shown in fig. 3, the one-pass holmium-doped laser amplifier includes a chirped pulse stretcher 01, an optical isolator 02, a holmium-doped crystal 03, a fiber collimator 04, a pump source 05, a chirped pulse compressor 06, a dichroic beam splitter 07, and a sixth mirror 08;
seed light of 2.05 μm generated by a previous unit (seed light generating and amplifying unit) is input into a chirped pulse stretcher 01 (a chirped Bragg grating is generally selected) to obtain a stretching amount of hundreds of picoseconds, and the seed light enters a holmium-doped crystal 03 for amplification after passing through an optical isolator 02; and finally, the light is reflected to a chirped pulse compressor 06 by the dichroic beam splitter 07 and a sixth reflecting mirror 08, and is output after pulse width compression. Wherein, the pumping source 05 is a thulium-doped continuous laser, the output of which is collimated by the optical fiber collimator 04 and enters the holmium-doped crystal 03 through the dichroic beam splitter 07 to realize pumping.
(2) Bi-pass holmium-doped laser amplifier
As shown in fig. 4, the two-pass holmium-doped laser amplifier includes a chirped pulse stretcher 01, an optical isolator 02, a polarization beam splitter 09, a holmium-doped crystal 03, a quarter-wave plate 010, a fiber collimator 04, a pump source 05, a chirped pulse compressor 06, a 0o mirror 011, a dichroic beam splitter 07, and a seventh mirror 012;
seed light of 2.05 μm generated by a previous unit (seed light generating and amplifying unit) is input into a chirped pulse stretcher 01 (chirped Bragg grating is generally selected) to obtain stretching amount of hundreds of picoseconds, and the seed light passes through an optical isolator 02 and a polarization beam splitter 09 and then enters a holmium-doped crystal 03 for amplification; then, the light is reflected by the dichroic beam splitter 07, passes through the quarter-wave plate 010 (the crystal axis direction and the laser polarization direction form 45 degrees), and reaches the 0-degree reflector 011, and the reflected light passes through the quarter-wave plate 010 again to rotate the polarization direction of the laser by 90 degrees; thereafter, the laser light will be amplified again in the reverse direction by the dichroic beam splitter and the holmium-doped crystal 03; finally, the reflected light is reflected by the polarization beam splitter 09 to the seventh mirror 012, and then reflected to the chirp pulse compressor 06 for pulse width compression and output. Wherein, the pumping source 05 is a thulium-doped continuous laser, the output of which is collimated by the optical fiber collimator 04 and enters the holmium-doped crystal 03 through the dichroic beam splitter 07 to realize pumping.
(3) Multi-pass holmium-doped laser amplifier
As shown in fig. 5, the multipass holmium-doped laser amplifier (5-pass in the figure may be more than or less than 5-pass depending on specific parameters) includes a chirped pulse stretcher 01, an optical isolator 02, a holmium-doped crystal 03, a fiber collimator 04, a pump source 05, a chirped pulse compressor 06, a mirror M1, a mirror M2, a mirror M3, a mirror M4, a mirror M5, a mirror M6, a mirror M7, a mirror M8, a mirror M9, a mirror M10, a mirror M11, and a mirror M12;
seed light of 2.05 μ M generated by a previous unit (seed light generating and amplifying unit) is input into a chirped pulse stretcher 01 (a chirped Bragg grating is generally selected) to obtain stretching amount of hundreds of picoseconds, and the seed light is reflected by mirrors M6 and M3 after passing through an optical isolator 02 and enters a holmium-doped crystal 03 for amplification; then the pulse is reflected by mirrors M9, M7, M5, M2, M10, M8, M4 and M1 in sequence, amplified by the holmium-doped crystal 03 for multiple times, and finally reflected by the mirrors M11 and M12 to a chirp pulse compressor 06 for pulse width compression and output. Wherein, the pumping source 05 is a thulium-doped continuous laser, and the output of the thulium-doped continuous laser enters the holmium-doped crystal 03 to realize pumping after being collimated by the optical fiber collimator 04. The figure shows a 5-way amplification structure, and the number of amplification ways can be increased or decreased by increasing or decreasing the number of reflectors according to the actual amplification requirement.
Medium-long wave broadband signal light generation unit
As shown in fig. 6, the medium-long wavelength broadband signal light generating unit includes a fourth beam splitter 25, a fifth mirror 26, a second focusing mirror 27, a second spectrally broadening material 28, a second collimating mirror 29, a fourth dispersive element 30, a third difference frequency crystal 31, a fifth dispersive element 32, and a third mirror group 33;
an incident beam is divided into two beams of light by a fourth beam splitter 25, wherein a fifth reflector 26, a second focusing mirror 27, a second spectrum broadening material 28, a second collimating mirror 29, a fourth dispersion element 30 and a third difference frequency crystal 31 are sequentially arranged on the light path of one beam of light;
the other beam of light sequentially passes through the fifth dispersion element 32 and the third mirror group 33 to enter the third difference frequency crystal 31, thereby generating a medium-long wave broadband signal light.
The working principle is as follows: the femtosecond pulse (the pulse wavelength is 800nm or 1 μm, and the single pulse energy is above the milli-focus level) output by the near-infrared ultrashort pulse laser source is divided into two beams by the fourth beam splitter 25. One of the laser beams is reflected by a fifth reflector 26, and then is focused by a second focusing mirror 27 into a second spectrum broadening material 28 (such as a KTA crystal) to realize spectrum broadening, and then is collimated by a second collimating mirror 29, and then is subjected to adjustment of the dispersion amount contained in the pulse by a fourth dispersion element 30; the other laser beam enters the fifth dispersion element 32 to adjust the dispersion amount and passes through the third mirror group to adjust the optical delay. Finally, the two laser beams realize time synchronization and space coincidence in the third difference frequency crystal 31, and the long-wave spectral components in the ultra-wide spectrum and the near-infrared pulse are subjected to a difference frequency process to obtain signal light with the wavelength of more than 2.5 mu m. The third mirror group 33 is an optical delay line, which adjusts the precise coincidence of the two lights in terms of time. In addition, in order to finally obtain a broad-spectrum, narrow-pulse-width femtosecond pulse output of >2.5 μm, the key of this part is to adjust the dispersion amounts of the fourth and fifth dispersion elements 30 and 32, and to achieve phase matching of the broad spectrum in the third difference frequency crystal 31.
A long-wave attosecond driving source is researched, and the attosecond pulse generating technology needs the driving source to have the characteristics of narrow pulse width and stable carrier envelope phase as far as possible. The intermediate-long wave signal light is idle frequency light with the wavelength of 2.5 microns generated by the spread spectrum of the front-stage ultrashort pulse amplification pulse light through a difference frequency process, and the carrier envelope phase of the idle frequency light is passively stable.
Double chirp amplification unit
As shown in fig. 7, the double-chirped amplification unit includes a sixth dispersive element 34, a fourth difference frequency crystal 35, a dispersion compensation device 36, a seventh dispersive element 37, and a fourth mirror group 38;
a sixth dispersion element 34, a fourth difference frequency crystal 35 and a dispersion compensation device 36 are sequentially arranged on the light path of the medium-long wave broadband signal light; the pumping light sequentially passes through the seventh dispersion element 37 and the fourth mirror group 38 and then enters the fourth difference frequency crystal 35, so as to generate the medium-long wave infrared femtosecond pulse.
The working principle is as follows: the generated time-domain broadened light of the 2.5 μm intermediate-long wave broadband signal light and the 2.05 μm pump light after passing through the sixth dispersive element 34 and the seventh dispersive element 37 respectively is amplified to 2.5 μm intermediate-long wave infrared femtosecond pulses through an optical parametric process in the fourth difference frequency crystal 35, and time synchronization can be realized by adjusting the fourth reflector group 38. Finally, the dispersion compensation device 36 is used to perform dispersion compensation to achieve the purpose of compressing the pulse width. The compressor formed by the dispersion compensation device 36 can adopt a grating pair, a prism pair, a block material, a volume Bragg grating and a chirped mirror. And the fourth difference frequency crystal 35 can adopt a phosphorus germanium Zinc (ZGP) crystal, and utilizes a 2.05 μm picosecond pulse pump ZGP crystal amplified by a front-stage Ho: YLF to perform wide spectrum amplification on signal light with the wavelength of more than 2.5 μm. The sixth dispersion element 34 may employ a commercially available acousto-optic programmable logic device (AOPDF) for dispersion adjustment to broaden the pulse width to several picoseconds before the signal light enters the double-chirped optical parametric amplification. As AOPDF introduces negative dispersion in the wave band, the signal light is negative chirp pulse, and positive dispersion is provided by using bulk material silicon (Si) for compensation in the compression stage; and the high-order dispersion introduced by the silicon material can achieve the purpose of pre-compensation through the dispersion adjustable function of the AOPDF. The 2.05 μm pump light of the double-chirp optical parametric amplification can be inserted into a positive dispersion or negative dispersion material as the seventh dispersion element 37 to adjust the chirp amount thereof, thereby optimizing the spectral width and energy of the >2.5 μm amplified pulse.
Finally, it should be noted that the above description is only for describing the preferred embodiments of the present invention, and not for limiting the scope of the present invention, and that any changes and modifications made by those skilled in the art according to the above disclosure are all within the scope of the appended claims.
Claims (10)
1. A medium-long wave infrared femtosecond pulse generating and amplifying device is characterized in that: the device comprises a near-infrared ultrashort pulse laser light source, a first beam splitter, a first reflector, a seed light generating and amplifying unit, a holmium-doped laser amplifying unit, a medium-long wave broadband signal light generating unit, a second reflector and a double-chirp amplifying unit;
emergent light of the near-infrared ultrashort pulse laser light source is split into two paths after passing through the first beam splitter, one path of light beam enters the seed light generating and amplifying unit adopting the double-chirp light parametric amplification structure through the first reflector to generate narrow-band seed light, and then the narrow-band seed light enters the holmium-doped laser amplifying unit to become pump light; the other light path generates medium-long wave broadband signal light through a medium-long wave broadband signal light generating unit;
after the pumping light is reflected by the second reflector, the medium-long wave broadband signal light and the medium-long wave broadband signal light enter the double-chirp amplification unit together to generate medium-long wave infrared femtosecond pulses with energy reaching more than a millifocus level;
the working wavelength of the near-infrared ultrashort pulse laser source is 790nm or 1 mu m, and the single pulse energy is above the milli-focus level;
the wavelength of the narrow-band seed light is 2.05 mu m, and the single pulse energy of the narrow-band seed light is greater than the micro-focus level;
the wavelength of the pump light is 2.05 μm, and the single pulse energy can reach hundred millijoules;
the wavelength of the medium-long wave broadband signal light is more than 2.5 mu m, and the single pulse energy only needs a nano-focus level.
2. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 1, wherein: the seed light generating and amplifying unit comprises a second beam splitter, a third reflector, a first focusing mirror, a first spectrum broadening material, a first collimating mirror, a first dispersion element, a first difference frequency crystal, a filter, a second difference frequency crystal, a second dispersion element, a third beam splitter, a first reflector group, a fourth reflector and a second reflector group;
an incident beam is divided into two beams of light by a second beam splitter, wherein a third reflector, a first focusing mirror, a first spectrum broadening material, a first collimating mirror, a first dispersion element, a first difference frequency crystal, a filter and a second difference frequency crystal are sequentially arranged on the light path of one beam of light;
another beam of light is divided into two beams of light again through a third beam splitter, and one beam of light is injected into the first difference frequency crystal after sequentially passing through the second dispersive element and the first reflector group;
and the other beam of light is injected into the second difference frequency crystal after passing through the third dispersive element, the fourth reflector and the second reflector group in sequence, so that narrow-band seed light is generated.
3. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 2, wherein: the holmium-doped laser amplification unit is a one-way holmium-doped laser amplifier or a two-way holmium-doped laser amplifier or a multi-way holmium-doped laser amplifier or a one-way, two-way and multi-way combined amplifier.
4. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 3, wherein: the medium-long wave broadband signal light generating unit comprises a fourth beam splitter, a fifth reflector, a second focusing mirror, a second spectrum broadening material, a second collimating mirror, a fourth dispersion element, a third difference frequency crystal, a fifth dispersion element and a third reflector group;
an incident beam is divided into two beams of light through a fourth beam splitter, wherein a fifth reflector, a second focusing mirror, a second spectrum broadening material, a second collimating mirror, a fourth dispersive element and a third difference frequency crystal are sequentially arranged on the light path of one beam of light;
the other beam of light is incident to the third difference frequency crystal through the fifth dispersion element and the third reflector group in sequence, so that the medium-wavelength broadband signal light is generated.
5. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 4, wherein: the double-chirp amplification unit comprises a sixth dispersion element, a fourth difference frequency crystal, a dispersion compensation device, a seventh dispersion element and a fourth reflector set;
a sixth dispersion element, a fourth difference frequency crystal and a dispersion compensation device are sequentially arranged on the light path of the medium-long wave broadband signal light;
the pumping light sequentially passes through the seventh dispersion element and the fourth reflector group and then is incident to the fourth difference frequency crystal, so that the intermediate-wavelength infrared femtosecond pulse is generated.
6. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 5, wherein: the near-infrared ultrashort pulse laser light source is a solid ultrashort pulse laser.
7. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 6, wherein: the first difference frequency crystal, the second difference frequency crystal and the third difference frequency crystal are all made of barium metaborate, bismuth metaborate or periodically poled lithium niobate materials, and the fourth difference frequency crystal is made of phosphorus germanium zinc crystal.
8. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 7, wherein: the first dispersion element, the second dispersion element, the third dispersion element, the fourth dispersion element and the fifth dispersion element are block materials or grating pairs or prism pairs or chirped mirrors.
9. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 8, wherein: the sixth dispersive element and the seventh dispersive element are acousto-optic programmable logic devices.
10. The apparatus for generating and amplifying mid-wavelength infrared femtosecond pulses according to claim 9, wherein: the first spectrum broadening material adopts white gem; the second spectrum broadening materials are all made of potassium titanyl arsenate crystals or white gems.
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