A method and apparatus for generating an ultra-short single attosecond pulse
By using generalized dual optical gating technology, the laser field components are separated using quartz waveplates, Brewster waveplates, and β-BBO crystals to generate asymmetric driving field components. This solves the problem of generating ultrashort single attosecond pulses in existing technologies, and achieves high-throughput and wide-bandwidth attosecond pulse output, which is suitable for IAP-NIR pump detection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-14
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies struggle to efficiently generate ultrashort single attosecond pulses in the laboratory, and the long-term locking of the carrier envelope phase CEP and the reduced flux of attosecond pulses generated by mid-infrared lasers limit their applications.
Using generalized dual-optical gating technology, the laser field components are separated and synthesized by short-wavelength pulsed lasers, quartz waveplates, Brewster waveplates and β-BBO crystals to generate asymmetric driving field components, forming a gating gate, and outputting an ultrashort single attosecond pulse.
It achieves high-throughput ultrashort single attosecond pulse generation that is independent of carrier envelope phase stability, overcomes the saturation ionization phenomenon of short-wavelength driving light, broadens the bandwidth of attosecond pulses, and is suitable for IAP-NIR pump-probe experiments.
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Figure CN119481921B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of stimulated radiation, in particular to a method and device for generating ultra-short single attosecond pulse. BACKGROUND
[0002] In order to obtain an ultra-high time resolution single attosecond pulse, a gating technique is required. This technique allows the emission of high-order harmonics only in half of the cycle by suppressing the emission of high-order harmonics in most of the fundamental light period, thereby selecting an isolated attosecond pulse. For example, the amplitude gating technique is a method for precisely controlling laser pulses, in which the width of the laser pulse is less than two optical periods, and the carrier envelope phase (CEP) can be precisely controlled. In this technique, due to the difference in electric field intensity in each optical period, only the half cycle in which the driving laser intensity reaches the peak value can generate an attosecond pulse with the highest photon energy (i.e. the spectral cutoff region). In contrast, when the driving laser is in other periods with weaker electric field intensity, the photon energy of the generated attosecond pulse will be relatively low. In short, this technique selectively uses the strongest part of the laser pulse to generate high-energy attosecond pulses, while ignoring the lower-energy parts.
[0003] The current laboratory scheme for generating ultra-short single attosecond pulses has strict requirements and corresponding technical drawbacks. On the one hand, it is difficult to achieve long-term locking of the carrier envelope phase (CEP) of the driving optical pulse in experimental techniques. On the other hand, most of the nearly 50 as ultra-short single attosecond pulses reported internationally are generated by increasing the wavelength of the driving light to improve the bandwidth. However, the flux of attosecond pulses generated by mid-infrared laser will also be sharply reduced, further limiting the application of attosecond pulses. SUMMARY
[0004] Therefore, the present application provides a method and device for generating ultra-short single attosecond pulses. The technical scheme provided by the present application introduces a generalized double optical gating device, which can generate a large flux of ultra-short single attosecond pulses under the driving of short-wavelength pulsed laser without carrier envelope phase (CEP) stabilization.
[0005] The present application provides a method for generating an ultra-short single attosecond pulse, comprising:
[0006] generating a few-cycle femtosecond pulse based on a femtosecond laser output module; the number of optical periods in the envelope of the few-cycle femtosecond pulse is not more than two; the few-cycle femtosecond pulse is linearly polarized near-infrared light;
[0007] processing the few-cycle femtosecond pulse based on a generalized double optical gating device to output a laser field pulse;
[0008] focusing the laser field pulse to a reaction cell to form a high-intensity laser field to ionize the gas in the reaction cell and generate an ultra-short single attosecond pulse.
[0009] The laser field pulse has a front part, a middle part and a tail part, the front part and the tail part are circularly polarized, the middle part is linearly polarized, forms a gate, the ultra-short single attosecond pulse is generated in the gate, and the width of the gate is less than 1 / 5 of the pulse width of the few-cycle femtosecond pulse.
[0010] Specifically, the step of processing the few-cycle femtosecond pulse based on the generalized double optical gate comprises:
[0011] The few-cycle femtosecond pulse is divided into a driving field component and a gating field component based on a quartz wave plate; the polarization direction of the driving field component is parallel to the polarization direction of the few-cycle femtosecond pulse, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-cycle femtosecond pulse; the phase delay between the driving field component and the gating field component is an integer multiple of an optical period;
[0012] A portion of the driving field component is reflected using a Brewster wave plate;
[0013] A second harmonic is generated based on a beta-BBO crystal, and a laser field pulse is output;
[0014] The second harmonic has the same polarization direction as the driving field component, and the second harmonic and the driving field component are combined to form an asymmetric driving field component; the laser field pulse comprises the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than a quarter of an optical period and changes over time.
[0015] Further, the step of reflecting a portion of the driving field component using a Brewster wave plate comprises:
[0016] The thickness of the Brewster wave plate is selected so that the attenuation rate of the driving field component is between 20% and 40%.
[0017] The application also provides an apparatus for generating an ultra-short single attosecond pulse, which generates the ultra-short single attosecond pulse using the above method, and comprises a femtosecond laser output module, a generalized double optical gate and an excitation generation module;
[0018] The femtosecond laser output module comprises a femtosecond laser and a pulse compression module, and is used to generate a few-cycle femtosecond pulse; the few-cycle femtosecond pulse is a near-infrared short-wave pulse;
[0019] The generalized double optical gate is used to process the few-cycle femtosecond pulse to generate a laser field pulse; the generalized double optical gate comprises a Brewster wave plate; the gate width of the generalized double optical gate is less than 1 / 5 of the pulse width of the few-cycle femtosecond pulse.
[0020] The excitation generation module comprises an optical converging element and a reaction cell, which are used for focusing the laser field pulse to ionize the gas of the reaction cell to generate the ultra-short single attosecond pulse.
[0021] Specifically, the generalized double optical gating device comprises a quartz wave plate, a Brewster wave plate and a beta-BBO crystal arranged along an optical axis.
[0022] The quartz wave plate comprises a first quartz wave plate and a second quartz wave plate, which are used for dividing the incident few-cycle femtosecond pulse into a driving field component and a gating field component; the polarization direction of the driving field component is parallel to the polarization direction of the few-cycle femtosecond pulse, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-cycle femtosecond pulse; the phase delay between the driving field component and the gating field component is an integer multiple of an optical period.
[0023] The Brewster wave plate is arranged at a Brewster angle relative to the optical axis, and is used for reflecting a part of the driving field component.
[0024] The beta-BBO crystal is a type-I phase-matched beta-barium borate crystal, which is used for generating a second harmonic to output a laser field pulse.
[0025] The second harmonic has the same polarization direction as the driving field component, and the second harmonic and the driving field component are combined to form an asymmetric driving field component; the laser field pulse comprises the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than one fourth of an optical period and changes with time; the laser field pulse has a front part, a middle part and a tail part, the front part and the tail part are circularly polarized, and the middle part is linearly polarized to form a gating device, and the ultra-short single attosecond pulse is generated in the gating device.
[0026] Preferably, the femtosecond laser outputs a pulse with a pulse repetition frequency of 1 kHz, a center wavelength of 800 nm, a pulse width of 25 fs and a maximum output energy of 4.2 mJ; the few-cycle femtosecond pulse has a pulse width of 5 fs.
[0027] Preferably, the first quartz wave plate has a thickness of 178 μm, the second quartz wave plate has a thickness of 445 μm, the Brewster wave plate is a glass sheet with a thickness of 0.5 mm, and the beta-BBO crystal has a thickness of 141 μm.
[0028] Preferably, the optical converging element comprises a concave silver mirror, and the concave silver mirror has a focal length of 350 mm; the reaction cell comprises a neon gas cell.
[0029] The above technical solution provided by the application has the following beneficial effects:
[0030] The technical scheme of the present application transforms the traditional double optical gating into a generalized double optical gating, by setting the width of the generalized double optical gating, not only can the generation of single attosecond pulse be ensured not to be affected by the carrier envelope phase stability of the driving pulse, but also the ionization effect of gas molecules on the rising edge of the driving pulse is reduced, the saturated ionization phenomenon that cannot be overcome by the short wavelength driving pulse is avoided, so that the bandwidth and flux of the generated single attosecond pulse are simultaneously enhanced, and the ultra-short single attosecond pulse based on short wavelength driving is realized.
[0031] For femtosecond pulses, the carrier envelope phase stabilization technology is complex and difficult to operate, the technical scheme provided by the present application reduces the difficulty of generating ultra-short single attosecond pulse. More importantly, the ultra-short single attosecond pulse generated by using the technical scheme provided by the present application is phase-locked with the driving pulse, and is suitable for IAP-NIR pump-probe experiment. BRIEF DESCRIPTION OF DRAWINGS
[0032] Figure 1 It is a flowchart of the method for generating ultra-short single attosecond pulse of the embodiment of the present application;
[0033] Figure 2 It is a flowchart of the method for processing the few-cycle femtosecond pulse of the embodiment of the present application;
[0034] Figure 3 It is a waveform diagram of the gating field component and the driving field component of the embodiment of the present application;
[0035] Figure 4 It is a structural schematic diagram of the generating device of the ultra-short single attosecond pulse of the embodiment of the present application;
[0036] Figure 5 It is a structural schematic diagram of the generalized double optical gating of the embodiment of the present application;
[0037] Figure 6 It is a pulse width diagram of the ultra-short single attosecond pulse of the embodiment of the present application;
[0038] The various reference numerals in the drawings represent:
[0039] 21, first quartz wave plate; 22, second quartz wave plate; 23, Brewster wave plate; 24, beta-BBO crystal; 31, concave silver mirror; 32, neon gas cell; 41, zirconium film; 42, gold-plated tire mirror; 43, hollow beam combining mirror; 44, focusing lens; 45, neon gas target; 46, time-of-flight spectrometer; 101, few-cycle femtosecond pulse; 201, laser field pulse; 301, single attosecond pulse; 401, fringe field. DETAILED DESCRIPTION
[0040] With reference to the drawings and embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.
[0041] Embodiment one
[0042] Please refer to the drawings Figure 1 , Figure 1 is a flowchart of a method for generating an ultra-short single attosecond pulse 301 provided by the present application. The method in the embodiments of the present application can be applied to an ultra-short single attosecond pulse 301 generating device. As can be seen from the figure, the method for generating an ultra-short single attosecond pulse 301 in the embodiments of the present application comprises:
[0043] S10: generating a few-cycle femtosecond pulse 101 based on a femtosecond laser output module;
[0044] In one or other embodiments of the present application, the number of optical cycles of the envelope of the few-cycle femtosecond pulse 101 is not more than two; the few-cycle femtosecond pulse 101 is linearly polarized near-infrared light;
[0045] S20: processing the few-cycle femtosecond pulse 101 based on a generalized double optical gating, and outputting a laser field pulse 201;
[0046] S30: focusing the laser field pulse 201 to a reaction cell to form a high-intensity laser field to ionize the reaction cell gas, and generating an ultra-short single attosecond pulse 301;
[0047] In one or other embodiments of the present application, the width of the gating is less than 1 / 5 of the pulse width of the few-cycle femtosecond pulse.
[0048] Please refer to the drawings Figure 2 , Figure 2 is a flowchart of a method for processing the few-cycle femtosecond pulse 101 according to the embodiments of the present application. As can be seen from the figure, the specific steps of the method for processing the few-cycle femtosecond pulse 101 based on a generalized double optical gating according to the embodiments of the present application comprise:
[0049] S201: splitting the few-cycle femtosecond pulse 101 into a driving field component and a gating field component based on a quartz wave plate; the polarization direction of the driving field component is parallel to the polarization direction of the few-cycle femtosecond pulse 101, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-cycle femtosecond pulse 101; the phase delay between the driving field component and the gating field component is an integer multiple of an optical period;
[0050] S202: reflecting a part of the driving field component by using a Brewster wave plate 23;
[0051] S203: generating a second harmonic based on a barium borate crystal, and outputting a laser field pulse 201;
[0052] wherein the second harmonic has the same polarization direction as the driving field component, and the second harmonic and the driving field component synthesize an asymmetric driving field component; the laser field pulse 201 includes the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than one fourth of an optical period and changes over time. In the above steps, since the Brewster wave plate 23 reflects a part of the driving field component, the intensity of the gating field component relatively increases, and thus the intensity of the second harmonic generated by the gating field component also relatively increases, so that the asymmetry of the synthesized asymmetric driving field component is enhanced, the ionization effect of the front part of the laser field pulse 201 on the gas molecules is reduced, more gas molecules can be excited within the narrow interval of the gating gate, the short-wavelength driving is compensated for the disadvantage of easy saturation ionization, the bandwidth of the generated single attosecond pulse 301 is increased, and thus the super-short single attosecond pulse 301 is generated.
[0053] Please refer to the accompanying drawings Figure 3 , Figure 3 The figure is a waveform diagram of the gating field component and the driving field component of the embodiment of the present application. In the figure, the gray line represents the driving field component, the black line represents the gating field component, the horizontal coordinate is time in femtoseconds, and the vertical coordinate is electric field intensity (arbitrary unit). See Figure 3 (a), after the few-cycle femtosecond pulse 101 passes through the first quartz wave plate 21, it is split into the gating field component and the driving field component with perpendicular polarization directions and a phase difference of two optical periods, wherein the electric field amplitude of the driving field component presents an up-down symmetric shuttle shape, and the maximum amplitude of the gating field component is weaker than that of the driving field component, and presents a shape of large at both ends and zero in the middle in the time domain. See Figure 3 (b), the second quartz wave plate 22 additionally introduces a phase delay of five optical periods. See Figure 3(c), the phase delay of the driving field component and the gating field component is compensated in the β-BBO crystal 24. In one or other embodiments of the present application, the driving field component is reduced by about 30% of the energy, and is combined with the second harmonic to form an asymmetric driving field component. In one or other embodiments of the present application, the gating field component generates the second harmonic after passing through the β-BBO crystal 24, and the remaining part forms a very narrow gating window near the time zero.
[0054] In addition, the generalized double optical gating window of the embodiments of the present application sets a gating window width small enough, in one embodiment of the present application, the gating window width is set to 1 fs, and in one or other embodiments of the present application, the gating window width can be set shorter. In this way, the process of generating the ultra-short single attosecond pulse 301 is not affected by the carrier envelope phase stability in the few-cycle femtosecond pulse 101, so that a shorter wavelength few-cycle pulse can be used as the driving light of the ultra-short single attosecond pulse 301, and the flux of the generated ultra-short single attosecond pulse 301 is improved.
[0055] The e light propagates faster than the o light in the β-BBO crystal 24, and in the β-BBO crystal 24 of the embodiments of the present application, a quarter of the phase delay is generated between the o light and the e light, that is, after passing through the β-BBO crystal 24, the phase delay of the gating field component and the asymmetric driving field component changes, and due to the introduction of the second harmonic, the phase delay of the gating field component and the asymmetric driving field component changes with time. Therefore, the laser field pulse 201 composed of the gating field component and the asymmetric driving field component is divided into a front part, a middle part and a tail part due to the change of the phase delay. In the central region of the middle part of the laser field pulse 201, the gating field component is zero, at this time, the laser field pulse 201 is linearly polarized. In the front part and the tail part of the laser field pulse 201, it is circularly polarized. The input few-cycle femtosecond pulse 101 is pre-chirped to compensate, and the gating field component and the driving field component become shorter when propagating in the optical device.
[0056] In one or other embodiments of the present application, the step of reflecting a part of the driving field component using the Brewster wave plate 23 includes selecting the thickness of the Brewster wave plate 23, so that the attenuation rate of the driving field component is between 20% and 40%.
[0057] Embodiment two
[0058] Please refer to the accompanying Figure 4 and the accompanying Figure 5 , Figure 4 is a structure schematic diagram of an ultra-short single attosecond pulse 301 generating device of an embodiment of the present application, Figure 5It is a schematic structural diagram of a generalized dual-optical gating device according to an embodiment of the present application. As shown in the figure, the device comprises a femtosecond laser output module, a generalized dual-optical gating device and an excitation generation module.
[0059] The femtosecond laser output module comprises a femtosecond laser and a pulse compression module, and is configured to generate a few-cycle femtosecond pulse 101.
[0060] In one or other embodiments of the present application, the femtosecond laser is a commercial titanium-sapphire laser, the output pulse repetition frequency of which is 1 kHz, the center wavelength is 800 nm, the pulse width is 25 fs, and the maximum output energy is 4.2 mJ. The infrared femtosecond pulse generated by the femtosecond laser is subjected to spectral broadening processing and pulse width compression processing by the pulse compression module, and a few-cycle femtosecond pulse 101 is output, the pulse width of the few-cycle femtosecond pulse 101 being 5 fs. In the embodiment of the present application, the few-cycle femtosecond pulse 101 is linearly polarized light.
[0061] The generalized dual-optical gating device is configured to process the few-cycle femtosecond pulse 101 to generate a laser field pulse 201.
[0062] Specifically, in one or other embodiments of the present application, the generalized dual-optical gating device comprises a quartz wave plate, a Brewster wave plate 23 and a β-BBO crystal 24 arranged along an optical axis.
[0063] The quartz wave plate comprises a first quartz wave plate 21 and a second quartz wave plate 22, and is configured to divide the incident few-cycle femtosecond pulse 101 into a driving field component and a gating field component; the polarization direction of the driving field component is parallel to the polarization direction of the few-cycle femtosecond pulse 101, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-cycle femtosecond pulse 101; the phase delay between the driving field component and the gating field component is an integer multiple of an optical period.
[0064] The Brewster wave plate 23 is arranged at a Brewster angle with respect to the optical axis, and is configured to reflect a portion of the driving field component.
[0065] The β-BBO crystal 24 is a type-I phase-matched barium borate crystal, and is configured to generate a second harmonic to output the laser field pulse 201.
[0066] Preferably, in one or other embodiments of the present application, the thickness of the first quartz wave plate 21 is 178 μm, the thickness of the second quartz wave plate 22 is 445 μm, the Brewster wave plate 23 is a glass sheet with a thickness of 0.5 mm, and the thickness of the β-BBO crystal 24 is 141 μm.
[0067] The second harmonic wave is the same as the polarization direction of the driving field component, and the second harmonic wave and the driving field component synthesize an asymmetric driving field component; the laser field pulse 201 includes the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than one fourth of the optical period, and changes over time; wherein the laser field pulse 201 has a front part, a middle part and a tail part, the front part and the tail part are circularly polarized, the middle part is linearly polarized, forming a gating, and the super-short single attosecond pulse 301 is generated in the gating, and the width of the gating is less than 1 / 5 of the pulse width of the few-cycle femtosecond pulse.
[0068] The excitation generation module includes an optical focusing element and a reaction cell, which is used to focus the laser field pulse 201 to ionize the gas in the reaction cell, and generate a super-short single attosecond pulse 301.
[0069] In one or other embodiments of the present application, the optical focusing element includes a concave silver mirror 31, and the focal length of the concave silver mirror 31 is 350 mm. In one or other embodiments of the present application, the reaction cell includes a neon gas cell 32. The laser field pulse 201 is focused into the neon gas cell 32 through the concave silver mirror 31, and reaches a high-intensity laser electric field of 4PW / cm2, thereby generating a single attosecond pulse 301.
[0070] The embodiment of the present application can generate a near-50-as super-short single attosecond pulse 301 through a generalized double optical gating, so that the entire process can generate a near-50-as super-short single attosecond pulse 301 without relying on the CEP-stable near-infrared pulse, and in the entire process, the width of the generalized double optical gating can be set to be narrow enough to ensure that the driving light for generating the super-short single attosecond pulse 301 does not rely on the carrier envelope phase CEP, while reducing the ionization effect of the rising edge of the near-infrared pulse, effectively overcoming the limitations of short-wavelength driving light in saturated ionization, and thereby significantly widening the bandwidth of the attosecond pulse. Therefore, not only does it open up a novel and efficient way to prepare a near-50-as super-short single attosecond pulse 301, but it also indicates great potential in improving the optical flux of the super-short attosecond pulse in the future. Optionally, generating a carrier envelope phase-stable femtosecond pulse is a complex and difficult technical operation, and the method of the present application for generating a near-50-as super-short single attosecond pulse 301 without relying on the CEP-stable near-infrared pulse greatly simplifies the difficulty of generating a super-short single attosecond pulse 301. More importantly, the super-short single attosecond pulse 301 generated by the method is phase-locked with the near-infrared driving pulse, and therefore is suitable for use in IAP-NIR pump-probe experiments.
[0071] Embodiment three
[0072] The embodiment of the present application provides an attosecond pulse characterization module for acquiring and detecting the pulse width and other parameters of the attosecond pulse generated in the embodiment one and the embodiment two.
[0073] Please refer to the accompanying drawings Figure 4 , Figure 4 The light pulse output from the reaction cell in the embodiment passes through the zirconium film 41, and on one hand, the chirp compensation is performed to eliminate the group dispersion effect within the single attosecond pulse 301, and on the other hand, the residual femtosecond pulse light can be isolated. In one or other embodiments of the present application, the intensity at the focal point of the laser field pulse 201 is adjusted to 2.5 PW / cm2, so that the photon energy is kept at 150 eV. The chirp compensation is performed by using the negative group delay dispersion characteristics of the zirconium film 41 below 150 eV. In the embodiment of the present application, the single attosecond pulse 301 and the stripe field 401 after the chirp compensation are focused to the neon gas target 45 by the gold-coated tire mirror 42, the hollow beam combiner 43 and the focusing lens 44, and then the electron spectrum is measured by using the time-of-flight spectrometer 46 with a step length of 211 as in the time delay range of 10.9 fs.
[0074] In one or other embodiments of the present application, the metal zirconium film 41 with a thickness of 200 nm is used to filter the residual few-cycle femtosecond pulse 101 and compensate the inherent chirp of the attosecond pulse. The attosecond pulse is focused to the neon gas target 45 by using the tire mirror with a focal length of 270 mm. At the same time, another focused near-infrared pulse (usually referred to as the stripe field 401) is combined with the attosecond pulse by the hollow silver mirror. The electron beam is generated by modulating the single-photon ionization of neon atoms by the stripe field 401, and the electron spectrum is measured by using the time-of-flight spectrometer 46 with the change of the IAP-NIR delay, that is, the attosecond stripe. The spectrum phase can be inverted from the attosecond stripe spectrum by various inversion methods, and then the time-domain waveform of the single attosecond pulse 301 is reconstructed, so that the time-domain characterization of the single attosecond pulse 301 is realized.
[0075] Due to the instability of the CEP, the electron counting rate is very low, and the electron spectrum at each delay is measured by integrating 50000 laser shots. The pump-probe time delay belongs to active phase locking, and the root mean square of the measured time jitter is 25 as. The electric field, pulse width, phase and other parameters of the single attosecond pulse 301 are obtained by using the fast inversion algorithm for the broadband attosecond pulse, so that the pulse width of the single attosecond pulse 301 is determined. Please refer to the accompanying drawings Figure 6 , Figure 6 The figure is the pulse width diagram of the ultra-short single attosecond pulse 301 in the embodiment of the present application. As shown in the figure, the pulse width of the attosecond pulse obtained by the ultra-short single attosecond pulse 301 generating device in the embodiment one and the embodiment two of the present application is about 51 as.
[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features therein can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims
1. A method for generating an ultrashort single attosecond pulse, characterized in that, The method includes: The few-period femtosecond pulses are generated based on a femtosecond laser output module; the number of optical periods in the envelope of the few-period femtosecond pulses is less than two; the few-period femtosecond pulses are linearly polarized near-infrared short-wave pulses. The few-period femtosecond pulse is processed using a generalized dual optical gating gate to output a laser field pulse; the laser field pulse includes a driving field component, a gating field component, and a second harmonic; the processing steps include reflecting a portion of the driving field component using a Brewster waveplate. The laser pulse is focused onto the reaction cell to form a high-intensity laser field that ionizes the gas in the reaction cell, generating an ultrashort single attosecond pulse. The laser field pulse has a front, a middle and a tail. The front and the tail are circularly polarized, and the middle is linearly polarized, forming a gating gate. The ultrashort single attosecond pulse is generated within the gating gate, and the width of the gating gate is no greater than 1 / 5 of the pulse width of the few-period femtosecond pulse.
2. The method for generating an ultrashort single attosecond pulse according to claim 1, characterized in that, The step of processing the few-period femtosecond pulse based on the generalized dual optical gating gate further includes: The few-period femtosecond pulse is divided into a driving field component and a gating field component based on a quartz waveplate; the polarization direction of the driving field component is parallel to the polarization direction of the few-period femtosecond pulse, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-period femtosecond pulse; the phase delay between the driving field component and the gating field component is an integer multiple of the optical period. The second harmonic is generated based on the barium borate crystal, and a laser field pulse is output. Wherein, the second harmonic and the driving field component have the same polarization direction, and the second harmonic and the driving field component combine to form an asymmetric driving field component; the laser field pulse includes the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than one-quarter of the optical period and varies with time.
3. The method for generating an ultrashort single attosecond pulse according to claim 2, characterized in that, The step of using a Brewster waveplate to reflect a portion of the driving field component includes: The thickness of the Brewster waveplate is selected such that the attenuation rate of the driving field component is between 20% and 40%.
4. A device for generating an ultrashort single attosecond pulse, comprising generating an ultrashort single attosecond pulse using the method described in claim 1, characterized in that, Includes a femtosecond laser output module, a generalized dual optical gating gate, and an excitation generation module; The femtosecond laser output module includes a femtosecond laser and a pulse compression module, used to generate short-period femtosecond pulses; the short-period femtosecond pulses are near-infrared short-wave pulses. The generalized dual optical gating gate is used to process few-period femtosecond pulses to generate laser field pulses; the generalized dual optical gating gate includes a Brewster waveplate; the gating gate width of the generalized dual optical gating gate is no greater than 1 / 5 of the pulse width of the few-period femtosecond pulse; The excitation generation module includes an optical focusing element and a reaction cell, used to focus the laser field pulse to excite the reaction cell to generate an ultrashort single attosecond pulse.
5. The device for generating an ultrashort single attosecond pulse according to claim 4, characterized in that, The generalized dual optical gate also includes a quartz waveplate and a barium metaborate crystal arranged along the optical axis; The quartz waveplate includes a first quartz waveplate and a second quartz waveplate, used to divide the incident few-period femtosecond pulse into a driving field component and a gating field component; the polarization direction of the driving field component is parallel to the polarization direction of the few-period femtosecond pulse, and the polarization direction of the gating field component is perpendicular to the polarization direction of the few-period femtosecond pulse; the phase delay between the driving field component and the gating field component is an integer multiple of the optical period; The Brewster waveplate is set at a Brewster angle relative to the optical axis to reflect a portion of the driving field component; The barium metaborate crystal is a type I phase-matched barium metaborate crystal, used to generate second harmonics and output laser field pulses. Wherein, the second harmonic and the driving field component have the same polarization direction, and the second harmonic and the driving field component combine to form an asymmetric driving field component; the laser field pulse includes the gating field component and the asymmetric driving field component; the phase delay between the gating field component and the asymmetric driving field component is less than one-quarter of the optical period and varies with time; wherein, the laser field pulse has a front part, a middle part and a tail part, the front part and the tail part are circularly polarized, the middle part is linearly polarized, forming a gating gate, and the ultrashort single attosecond pulse is generated within the gating gate.
6. The device for generating an ultrashort single attosecond pulse according to claim 4, characterized in that, The femtosecond laser outputs a pulse repetition frequency of 1 kHz, a center wavelength of 800 nm, a pulse width of 25 fs, and a maximum output energy of 4.2 mJ; the few-period femtosecond pulse has a pulse width of 5 fs.
7. The device for generating an ultrashort single attosecond pulse according to claim 5, characterized in that, The first quartz waveplate has a thickness of 178 μm, the second quartz waveplate has a thickness of 445 μm, the Brewster waveplate is a glass plate with a thickness of 0.5 mm, and the barium metaborate crystal has a thickness of 141 μm.
8. The device for generating an ultrashort single attosecond pulse according to claim 5, characterized in that, The optical focusing element includes a concave silver mirror with a focal length of 350 mm; the reaction cell includes a neon gas cell.