CN100432643C - Femtosecond laser camera - Google Patents

Abstract

The present invention relates to a device for measuring various characteristics of a femtosecond pulse laser. The device of the present invention aims to solve the technical problems that the device can not accurately measure the width (vibration amplitude) of a femtosecond laser pulse, can not quickly measure the initial phase and the distribution thereof, can not visually detect the chirping state of the femtosecond laser pulse, the center frequency of carrier waves and the bandwidth of the spectrum, and can not draw out the waveform image of the femtosecond laser pulse. The device of the present invention has the technical scheme that a femtosecond laser camera is orderly provided with a mode converter, a lens and a spectrum phase modulator along the laser pulse direction of the laser input port of the camera, wherein one surface of the lens is used for transmission, and the other surface of the lens is used for reflection. The device of the present invention is also provided with a focusing lens and a Michelson interferometer with an attached time delay shutter, wherein the Michelson interferometer is arranged in the direction of the laser pulse reflected by the mode converter. The device of the present invention is orderly provided with the focusing lens, a frequency doubling crystal, a space filtering diaphragm, a gain selecting switch, a spectrograph and a video camera, wherein an interference autocorrelation receiver SHG is arranged in the direction of the laser pulse reflected by the gain selecting switch. In addition, the device of the present invention is matched with a computer.

Description

Femtosecond laser camera

Technical field

The present invention relates to a kind of device of measuring ultra-short pulse laser, especially can accurately measure pulsewidth, the quick device of the femtosecond pulse of Measurement Phase and characteristic such as warble.

Background technology

Ultra-short pulse laser is meant that generally pulse width is less than psec (ps, 10 at present ^-12Second) the following laser of magnitude.Since the sixties in last century, laser instrument came out, initial ultra-short pulse laser was several nanoseconds (ns, 10 that utilize the free-running laser generation of Q-switch ^-9Second) light of width, to the nineties, owing to invented kerr lens mode locking and orphan's mode-locking technique, and adopt the novel wide-band laser medium (as to mix titanium sapphire Ti:Al ₂O ₃) the solid self mode-locked laser, can directly produce several femtoseconds (fs, 10 ^-15Second) light of width.Because femtosecond pulse self has high time resolution characteristics and great peak energy, has been widely used in the research of various ultrafast phenomenas and the physical behavio(u)r under the high field.As the relaxation process of molecule, metabolic studies, reaction kinetics of photochemistry and the laser fusion etc. of biological cell.Yet the ultra-short pulse laser measuring technique but relatively lags behind at present.Up to now, owing to be subjected to the restriction (generally being about 1ps) of the time period resolution of electron detection technology, also without any a kind of instrument that can directly measure femtosecond pulse.In order to adapt to the measurement of the ultra-short pulse laser of doing narrower and narrower, people can only still adopt coherent detection technology.The basic thought of this technology is: utilize the measurement result that satisfies under optical coherence (or claiming relevant) condition, calculate the needed measurement information for the treatment of indirectly by mathematical method.Along with the develop rapidly of ultra-short pulse laser technology, the accurate measurement of femtosecond pulse has been become very urgent demand.Especially when pulse width very narrow (less than 10fs), not only need accurately to measure pulsewidth, and need measure information such as impulse phase and chirping characteristics simultaneously.Yet the traditional ultra-short pulse laser measurement mechanism (as two-photon fluorescence method, streak camera etc.) that can only measure pulsewidth can't be suitable for, and only has coherent method to be leveraged to the present.On the other hand, in the research field of femto-second laser,, must compensate as much as possible and warble in order to obtain burst pulse; Simultaneously, for fast and have the compensation of directivity ground to warble, compression pulse and improve pulse shape also needs the measurement mechanism that can measure impulse phase, chirping characteristics fast.Therefore, development and exploitation femtosecond pulse measuring technique, information such as intactly understand width, the phase place of femtosecond pulse and warble is most important content in the ultrafast technical research field.Explore through long-term, people have successively proposed many kinds of coherence detection.Wherein, topmost internationally recognized two kinds of standard femtosecond pulse measuring methods are: frequency resolution optical shoulder rotation (FROG) and the relevant direct electric field reconstruct method (SPIDER) in spectrum position.

Frequency resolution optical shoulder rotation (FROG) is a kind of coherence detection that can try to achieve information such as pulse width to be measured, phase place indirectly that proposes the nineties in last century.Its ultimate principle is: will be divided into two bundles by photometry, a branch of as surveying light, another bundle is introduced time delay τ as switch light, again two-beam is converged to produce in the nonlinear medium and interact, second order or the third-order non-linear effect of utilizing medium to produce, receive to survey light with switch light interactional and frequency light as flashlight, record the image (in fact it is a two-dimensional function relevant with time and frequency) of its light distribution through spectrometer and with ccd video camera again, utilize computing machine and adopt the interative computation just can be in the hope of measured pulse width and phase information.In the FROG method,, multiple different design proposal is arranged according to different photoswitch functions.Wherein, based on traditional second harmonic-frequency discrimination photoswitch method (SHG-FROG), be simple and easy to accent, highly sensitive, thereby be widely adopted.Specifically as shown in Figure 9: tested femtosecond pulse light beam G ₁Through beam splitter B ₁Be divided into two bundles: a branch ofly (comprise corner cube mirror M through Michelson interferometer ₁, M ₂, half-reflecting half mirror B ₁, mirror M ₃) in fixedly corner cube mirror M ₁, as surveying light; The movable corner cube mirror M of another bundle in Michelson interferometer ₂, as switch light (to introduce a time delay τ); And make that two-beam is parallel to be incided lens L1 and focus on nonlinear medium S ₁Produce in (BBO or KDP) and interact, after spectrometer T1 carries out spectral evolution, receive, thereby the intensity signal after obtaining interacting also is called SHG-FROG " trace spectrogram " by CCD.It is a series of different distributions that postpone the frequency spectrum of the moment, intensity autocorrelation signal along axle time delay, is expressed as with mathematical expression:

$I_{\mathrm{FROG}}(\mathrm{\ω},\mathrm{\τ})={\left|\underset{-\∞}{\overset{\∞}{\∫}}{E}_{\mathrm{sig}}(t,\mathrm{\τ})\exp \left(\mathrm{j\ωt}\right)\right|}^2={\left|E_{\mathrm{sig}}(\mathrm{\ω},\mathrm{\τ})\right|}^2$

Wherein: $E_{\mathrm{sig}}(t,\mathrm{\τ})=\tilde{E}\left(t\right)\tilde{E}(t-\mathrm{\τ})$ Envelope expression formula for flashlight.

$E\left(t\right)=\tilde{E}\left(t\right)\exp [-j\left({\mathrm{\ω}}_{c}t\right)-\stackrel{\→}{K}r]$ Be femtosecond pulse electric field expression formula to be measured.

ω _cBe center carrier frequencies,

Be wave vector,

Time domain complex envelope for femtosecond pulse to be measured.

In fact, I _FROG(ω τ) is E _Sig(t, the mould of Fourier transform τ) square.Thereby, by computing machine, and adopt iterative algorithm (normalized Gerchberg-Saxton algorithm) to obtain unique solution by SHG-FROG trace (take the photograph image) data, promptly can determine the pulsewidth and the phase information of femto-second laser pulse to be measured uniquely.Its advantage is that the result is accurate, and shortcoming is that speed is slower, is not suitable for real-time detection.

The relevant direct electric field reconstruct method of relevant direct electric field reconstruct method (SPIDER) in spectrum position or title self-reference spectrum position is a kind of method that can calculate impulse phase to be measured fast that proposes on the basis of spectrum coherent method the nineties in last century.Frenchman C.Froehly proposes the relevant notion of spectrum the earliest in the seventies in last century, its ultimate principle is, to satisfy the two-beam of coherent condition by the nonlinear medium effect, and with spectrometer (its effect is that the time domain light signal is transformed into the frequency domain light signal, being Fourier transform) (delay time T of the frequency interval of striped and two bundle coherent lights is inversely proportional to recording interference fringe, be 2 π/τ), if this interference fringe is carried out inverse fourier transform, and just can to obtain the spectrum phase of this two-beam poor, if the spectrum phase of known wherein a branch of reference light then can be obtained the spectrum phase of another bundle.But, in fact the spectrum phase of reference light also is unknown, so proposed self-reference spectrum coherent method again, be about to light pulse to be measured through Michelson interferometer, be copied into a pair of mirror image pulse with relative delay τ, but, still can't obtain the spectrum phase place of pulse because the spectrum phase difference between them is zero.Up to the nineties in last century, the self-reference spectrum coherent method of a kind of utilization " spectral tailoring " (being the SPIDER method) has solved the problems referred to above.The core of SPIDER method is: utilize the pulse strenching technology to manage to the additional known little frequency shift amount Ω of reference light, and make this frequency shift amount not influence the phase place of tested light pulse, utilize above-mentioned spectrum coherent method just can calculate the phase place of tested light pulse again.Specifically as shown in figure 10: measured laser pulse G ₂Through beam splitter B ₄Be divided into two-way, road light wherein reflexes to Michelson interferometer and (comprises fixedly corner cube mirror M ₄, and removable corner cube mirror M ₅, half-reflecting half mirror B ₂, B ₃) after be divided into that two bundles are identical to have a pulsed light that relative time postpones τ, this two beam pulse is photosynthetic and deliver to focus lamp L2 together; Another road pulsed light is by beam splitter B ₄Be transmitted through in the nonlinear medium as spectrum phase modulator J broadened, because the parameters such as abbe number as the dielectric material of spectrum phase modulator (also claiming stretcher) are known, so can realize as mentioned above to the additional known little frequency shift amount of reference light; Broadened and give the linear positive chirped pulse optical of frequency shift amount, through completely reflecting mirror M ₆, M ₇After the reflection, with the light pulse of last road to the parallel focus lamp L that incides ₂, and enter non-linear crystal S ₂Carry out frequency inverted, receive by spectrometer T2 afterwards; Because the time delay τ and the existence of warbling, make two beam pulse light on different frequencies and frequently, and produce a frequency difference at frequency domain, be called as spectrum shearing displacement (representing) with Ω; Spectrometer is noted the right interference spectum image (being also referred to as the SPIDER trace) of pulse that has spectrum shearing displacement Ω and is sent into computing machine and can draw phase value through simple operation.The mathematic(al) representation of SPIDER trace is:

$D(\mathrm{\ω},\mathrm{\τ})={\left|\tilde{E}({\mathrm{\ω}}_C-\mathrm{\Ω})\right|}^2+{\left|\tilde{E}\left({\mathrm{\ω}}_C\right)\right|}^2+2\left|\tilde{E}({\mathrm{\ω}}_C-\mathrm{\Ω})\right|\left|\tilde{E}\left({\mathrm{\ω}}_C\right)\right|\×\mathrm{COS}[\mathrm{\θ}\left({\mathrm{\ω}}_C\right)-\mathrm{\ω\τ}]$

Wherein

τ is that relative time postpones,

Be the 2nd order chromatic dispersion of stretcher,

With

Frequency-domain expression for the two-beam pulse.

Because the SPIDER method is less demanding to optical pulse energy, can be directly detect (need not the luminous power amplifier stage) from the output of laser instrument oscillator stage, and the processing computing of its reconstruct impulse phase does not need iterative algorithm, simple and fast, can be used as the instrument of the phase information of real-time detection light pulse, but the method can not directly provide information such as pulse width.

Summary of the invention

Technical matters to be solved by this invention is the deficiency that overcomes the above-mentioned background technology, a kind of femto-second laser pulse pick-up unit is provided, this device should be able to accurately be measured the width (amplitude) of femto-second laser pulse, measure initial phase and distribution thereof fast, the state of warbling, centre carrier frequency and the spectral bandwidth of visual inspection femto-second laser pulse, and can draw the waveform image of femto-second laser pulse.

The present invention has adopted following technical scheme:

Femtosecond laser camera, this camera has a laser input port, laser pulse direction along this port is disposed with mode converter, one side transmission another side catoptron and spectrum phase modulator, and a catoptron that transmits laser pulse is set between one side transmission another side catoptron institute's laser light reflected pulse direction and condenser lens, so that make this road laser pulse pass mode converter earlier, one side transmission another side catoptron is transported to the spectrum phase modulator and is carried out frequency and cut out, and is back to one side transmission another side catoptron then along former road and reflexes to condenser lens; Again at the Michelson interferometer of mode converter institute laser light reflected pulse direction setting with the time delay shutter, and set gradually described condenser lens in the laser pulse direction that Michelson interferometer is exported, frequency-doubling crystal BBO, the spatial filtering aperture, gain-selector switch and spectrometer, and interference autocorrelation receiver SHG is set in gain-selector switch institute laser light reflected pulse direction, also be furnished with computing machine and gamma camera CCD in addition, so that make another route pattern converter laser light reflected pulse pass Michelson interferometer earlier, and after merging, condenser lens enters that frequency-doubling crystal BBO carries out and frequently from parallel together being input to of Michelson interferometer output back and aforesaid road laser pulse that is reflected by one side transmission another side catoptron; Through restrainting laser pulses by being divided into two behind spatial filtering aperture, the gain-selector switch again with laser pulse frequently, the beam of laser pulse is passed gain-selector switch and is entered spectrometer, by gamma camera CCD shooting and deliver to the Computer Processing pictorial data, another bundle laser pulse is reflexed to by gain-selector switch and outputs signal to Computer Processing after interfering autocorrelation receiver SHG.

Be provided with the optical frames of the circle that can rotate around the center of circle in the described mode converter, wherein hemicycle is made completely reflecting mirror, hemicycle is made half-reflecting half mirror in addition, this mirror is by the precision electric motor drive and by computer control, so that the detected state of femtosecond laser camera is in perfect information pattern, instant phase pattern, warble state model or comparison pattern.

Be provided with the optical frames of the circle that can rotate around the center of circle in the described gain-selector switch, wherein 1/3 circle is made completely reflecting mirror, and 1/3 circle is made half-reflecting half mirror, and 1/3 circle is the full impregnated mirror, and this mirror is by the precision electric motor drive and by computer control.

Described time delay shutter comprises accurate screw rod leading screw, stepper motor, precise displacement sensor and the interlock circuit that is arranged in the oil-filled inner chamber, and is connected control with computing machine DN, also comprises the movable corner cube mirror in the Michelson interferometer.

Described spatial filtering aperture is a center pit area continuously controllable aperture, fixes with optics multidimensional adjusting bracket.

Described spectrum phase modulator comprises grating, corner cube mirror and the removable catoptron of mutual formation certain angle.

Pick-up unit provided by the invention has multiple measuring ability:

1, when mode converter is in " perfect information pattern ", the measuring ability with SHG-FROG method and SHG method.At this moment, the measured laser pulse is by the completely reflecting mirror regional reflex of the optical frames in the mode converter.Gain-selector switch can be selected two states: during the total transmissivity state, can measure the information of pulse width (amplitude), phase place, centre carrier frequency and the spectral bandwidth of tested femto-second laser pulse with the SHG-FROG method; When gain-selector switch selects half-reflection and half-transmission to penetrate state, can measure the information of pulse width (amplitude), centre carrier frequency and the spectral bandwidth of tested femto-second laser pulse with traditional SHG method.

2, when mode converter is in " state model of warbling ", has the status detection function of warbling.At this moment, the measured laser pulse is by the completely reflecting mirror regional reflex of the optical frames in the mode converter.Gain-selector switch can be selected the total reflection state, need enable the interference autocorrelation receiver again simultaneously, can completely accurately record the contained size of warbling of femto-second laser pulse and positive and negative, and can reach the effect of quantitative test.

3, when mode converter is in " instant phase pattern ", has SPIDER method measuring ability.At this moment, the half-reflecting half mirror zone of the optical frames in the mode converter is incided in the measured laser pulse, and gain-selector switch is selected the total transmissivity state, can obtain the phase information of measured laser pulse quickly and easily, can be used as real-time survey instrument.

4, when mode converter is in " comparison pattern ", have the detection and function relatively of same measured laser pulse being carried out SHG-FROG method, SPIDER method.At this moment, the mode converter that rotates by given pace is incided in the measured laser pulse, make that the measured laser pulse is well-regulated is back and forth penetrated by mode converter total reflection and half-reflection and half-transmission, gain-selector switch is the total transmissivity state, and can obtain the measurement result of two kinds of distinct methods (FROG method and SPIDER method).Therefore, can compare and measure result and judge its accuracy; Also the mean value that can adopt two kinds of resulting results of measuring method makes measurement data more near truth as final measurement.Thereby the present invention can be widely used in ultra-short pulse laser technology and application, the especially development of ultrashort pulse laser, production and debugging.

Description of drawings

Fig. 1 is a structural representation of the present invention.

Fig. 2 is the main TV structure synoptic diagram of the mode converter among the present invention.

Fig. 3 is the right TV structure synoptic diagram of this mode converter.

Fig. 4 is the structural representation of the time delay shutter among the present invention.

Fig. 5 is the main TV structure synoptic diagram of the gain-selector switch among the present invention.

Fig. 6 is the right TV structure synoptic diagram of this gain-selector switch.

Fig. 7 is the view of the present invention when being in " state model of warbling ".

Fig. 8 is the view of the present invention when being in " perfect information pattern ".

Fig. 9 is the schematic diagram of existing second harmonic frequency resolution optical shoulder rotation.

Figure 10 is the relevant direct electric field reconstruct ratio juris figure in existing spectrum position.

Embodiment

As shown in Figure 1, this femtosecond laser camera, having a laser pulse input port R (generally is the hollow aluminum pipe of one section inwall black coating, introducing path as the measured laser pulse, and MO becomes one with mode converter), input direction along the pulse of input port measured laser is disposed with mode converter MO, one side transmission another side catoptron BF and spectrum phase modulator (stretcher) GT, and the mirror M that a transmission laser pulse is given condenser lens L3 is set between one side transmission another side catoptron BF institute's laser light reflected pulse direction and condenser lens L3 ₁₂In mode converter institute laser light reflected pulse direction Michelson interferometer is set again and [comprises corner cube mirror M ₈, the movable corner cube mirror M that meets at right angles and arrange with this mirror ₉(for the part of time delay shutter YC) and beam splitter (also claiming half-reflecting half mirror) B ₆, B ₅], and set gradually described condenser lens L3, frequency-doubling crystal BBO, spatial filtering aperture GQ, gain-selector switch MG and spectrometer GPY in the laser pulse direction that Michelson interferometer is exported, and in gain-selector switch institute laser light reflected pulse direction interference autocorrelation receiver SHG is set, and is furnished with computing machine DN and gamma camera CCD.Arrow among the figure is the traffic direction of measured laser pulse, and arrow locations is the running route of measured laser pulse.

In Fig. 2, the mode converter shown in Figure 3, circular optical frames can rotate around central shaft, and becomes miter angle with input port hollow tubular center line and fixed by the function support.The hemicycle 2 of circular optical frames is made the total reflection minute surface, and hemicycle 1 is made the half-reflection and half-transmission minute surface in addition, and this mirror can be by stepper motor 3 driven rotary and by computer control.When needs were measured pulsewidth (amplitude), phase place, centre carrier frequency, the spectral bandwidth of pulse, the detected state of femtosecond laser camera should be in " perfect information pattern ", and this moment, mode converter was the total reflection minute surface; When needs were measured the pulse chirp characteristic, the detected state of femtosecond laser camera should be in " state model of warbling ", and this moment, mode converter also was the total reflection minute surface; When needs were measured impulse phase, the detected state of femtosecond laser camera should be in " instant phase pattern ", and this moment, mode converter was that half-reflection and half-transmission is penetrated minute surface; When needs are measured same pulse to be measured with two kinds of methods (FROG method and SPIDER method), the detected state of femtosecond laser camera should be in " comparison pattern ", at this moment, mode converter is one to be presented by given pace it by computer control to rotate, change into total reflection minute surface and half-reflection and half-transmission by turns and penetrate minute surface, the selection of above-mentioned pattern is decided as required by the operator.

Described spectrum phase modulator GT (also claiming stretcher) has various ways, as the deielectric-coating catoptron of nonlinear medium (being dispersive medium), Fabry-Perot etalon, special plated film and the grating+corner cube mirror of the present invention's employing etc. all is than mature technology, can directly adopt.Grating of the present invention+corner cube mirror structure, it comprises grating G (1200 lines/mm), the corner cube mirror M of mutual formation certain angle ₁₀And removable change is with respect to the completely reflecting mirror M of grating G distance ₁₁, wherein grating G and corner cube mirror M ₁₀Distance also adjustable.Enter the light of this phase-modulator GT, be by foregoing mode converter MO transmission by photometry.This light at first reflects the transmission plane of another side diaphotoscope BF through one side, incide the grating G among the described spectrum phase modulator GT and reflex to corner cube mirror M ₁₀, through M ₁₀Reflex to grating G, then reflexed to completely reflecting mirror M by grating G again ₁₁, by completely reflecting mirror M ₁₁Be back to grating G by former road, and reflex to corner cube mirror M by grating G by former road again ₁₀, again through M ₁₀The opposite grating G that is back to former direction, and, reflex to the reflecting surface that one side reflects another side diaphotoscope BF by the former light path that enters this phase-modulator GT.Therefore, the measured laser pulse in described phase-modulator GT altogether by optical grating reflection four times, then the mirror image light relative time that can calculate dispersion measure that phase-modulator GT provided, spectral tailoring amount Ω and described Michelson interferometer with the time delay shutter by known above-mentioned parameter such as relevant postpones the OK range value of τ, and it is stand-by to deposit computing machine in.

Described Michelson interferometer with the time delay shutter comprises corner cube mirror M ₈, the movable corner cube mirror M that meets at right angles and arrange with this mirror ₉And beam splitter (also claiming half-reflecting half mirror) B ₆, B ₅, wherein movable corner cube mirror M ₉It is the ingredient of time delay shutter YC, this time delay shutter (shown in Figure 4) comprises accurate screw rod leading screw 15, stepper motor 14, precise displacement sensor 11 and the interlock circuit that is arranged in the oil-filled inner chamber 13, and be connected control with computing machine DN, make stepper motor according to measuring the needs rotation and driving the screw rod leading screw and after the movable corner cube mirror M9 that links to each other moves corresponding distance, the CCD shutter is just taken once, carry out repeatedly successively, to obtain needed image with each correlation detection signal of time delay τ.

Described interference autocorrelation receiver SHG mainly comprises photodetector, A/D transducer.This interferes autocorrelation receiver SHG, after adding the Michelson interferometer part and computing machine among the present invention, the structure of being formed is just identical with existing Chinese patent (ZL200420110194.2), it can completely accurately record the contained size of warbling of femto-second laser pulse and positive and negative, can reach the effect of quantitative test, and can completely reproduce the complete waveform of " the humorous wave envelope of frequency discrimination auto-correlation secondary interference ", and it is, visual in image, be easy to understand into the people by the test result that image is expressed.

Described gain-selector switch MG, mainly be in order to enlarge the measuring ability of femtosecond laser camera, except as above-mentionedly make things convenient for, the visual inspection femto-second laser pulse chirping characteristics, " the completely reflecting mirror state " of described gain-selector switch MG and described autocorrelation receiver SHG, after adding the Michelson interferometer part and computing machine among the present invention, promptly formed the ultrashort laser pulse pick-up unit of traditional second harmonic auto-correlation (SHG) method.On the other hand, make it that flashlight that records is carried out beam splitting as required, perhaps carry out total reflection, total transmissivity to reach the loss that reduces the flashlight energy that records.As a kind of better simply structure, gain-selector switch MG can be the optical flat mirror of a collar plate shape that can rotate around central shaft, this optical frames minute surface becomes miter angle to place with the centerline direction of the introducing tube channel of femtosecond laser camera input port, and can finely tune on this direction or lock.This circle optics level crossing is equally divided into three equal parts, and wherein 1/3rd is that completely reflecting mirror 1/22nd, three is penetrated mirror the 1st/21st, three for half-reflection and half-transmission, empty (total transmissivity face 23).Gain-selector switch is by stepper motor 26 drives and by computer control, to adapt to the needs of measurement.

When being in " perfect information pattern " state at femtosecond laser camera when (state shown in Figure 8), the measured laser pulse is by mode converter MO, be totally reflected to described with in the Michelson interferometer of time delay shutter by MO, and be divided into two bundles by the beam splitter B6 in this interferometer, wherein a branch of fixedly corner cube mirror M8 that is entered into Michelson interferometer by beam splitter B6 reflection, its reflected light incides beam splitter B5 and is transmitted to described condenser lens L3 as detecting light beam; On the other hand, enter into light beam by beam splitter B6 transmission with the removable corner cube mirror M9 of the Michelson interferometer of time delay shutter, because of M9 is the ingredient of described time delay shutter YC, and can move respective distance along the oil-filled leading screw of precision according to measuring needs, thereby formed the light that has relative time delay τ with the detecting light beam of the above, with this light as switch light (obviously having just that relative time postpones τ and the mirror image pulse of not having any other difference) with above-mentioned detection light, reflex to reflection again behind the beam splitter B5 (make it and survey the light incident that is parallel to each other) to described condenser lens L3 by M9, the line focus lens incide be concerned with among the described frequency-doubling crystal BBO (or KDP) and conversion frequently after, again through the unwanted parasitic light of described spatial filtering aperture GQ filtering, what obtain incides described gain-selector switch MG[with the frequency flashlight and can select total transmissivity and half-reflection and half-transmission to penetrate two kinds of states (as shown in Figure 8, as to be represented by the flashlight with dashed lines arrow of MG half reflection) according to measuring needs MG]; When MG was total transmissivity, signal beams directly entered spectrometer GPY, and noted the two-dimentional spectrogram of intensity with respect to frequency and time by the CCD gamma camera.These data are after repeatedly interative computation is handled by computing machine, can obtain the information such as pulsewidth (amplitude), phase place, spectral bandwidth of measured laser pulse; When gain-selector switch MG is a half-reflection and half-transmission when penetrating, what obtain will be divided into two-way with the frequency signal beams: a route MG is transmitted to aforesaid spectrometer GPY and carries out aforesaid testing process, and another route MG reflexes to described completely reflecting mirror M ₁₃, and through M ₁₃Also output signal to Computer Processing after reflexing to described interference autocorrelation receiver SHG, provide the contained information of warbling of femto-second laser pulse.

When femtosecond laser camera is in " instant phase pattern ", incided mode converter MO by photometry after, present half-reflection and half-transmission and penetrate state, temporal gain selector switch MG is in the total transmissivity state.At this moment, the state of femtosecond laser camera is basic identical with Fig. 1, only is at temporal gain selector switch MG and completely reflecting mirror M ₁₃Between do not have flashlight.

When femtosecond laser camera is in " state model of warbling " (state shown in Figure 7), incided mode converter MO by photometry after, present the total reflection state, the temporal gain selector switch also is in the total reflection state, and opens and interfere autocorrelation receiver SHG.

When femtosecond laser camera was in " comparison pattern ", mode converter MO then rotated by given pace, makes by photometry alternately to be half-reflection and half-transmission and total reflection state, and the temporal gain selector switch is in the total transmissivity state.

Above-described all kinds of optical frames all should satisfy the spectral bandwidth requirement of measuring needs, and adopts the little quartz material of absorption loss.Wherein, the thickness of non-linear frequency-doubling crystal (BBO or KDP etc.) is about 100 μ m, and one side transmission another side catoptron in the wavelength coverage enough wide by the carrier wave center frequency-band of photometry, accomplishes to have consistent sufficiently high transmissivity and reflectivity as much as possible.It is worthy of note that accurate for the measurement result that makes instrument, the precision of each parts all will have higher requirements, satisfy the pacing items of optics as much as possible from Coherent Detection.For example, the mirror surface flatness should be better than 1/50 wavelength, delay system is guaranteed stable not shake, adopt oil-filled precision lead screw, delay shutter and spatial filtering aperture, corresponding optical frames to be installed on locking, coarse adjustment fine setting, the three-dimensional multidimensional minute adjustment frame, be convenient to install and regulate, important light path need be taked measures such as dustproof lucifuge, thus signal to noise ratio (S/N ratio) (S/N), accuracy of detection and the sensitivity that can improve measuring system.

Should be noted that: for guarantee detecting accurately, whole table apparatus should be arranged on the shockproof optical table, should guarantee during measurement that complete machine is airtight light tight, avoids surrounding environment to have the generation etc. of vibroseis also to be very important simultaneously as far as possible.

Still it should be noted that: remove gain-selector switch MG, mode converter, time delay soon outdoors, the equal buyable of all the other all components and parts and material obtains; Required computer software also can be worked out by ordinary procedure person.

Several testing process of the present invention is:

1, when " perfect information pattern ", tested femto-second laser pulse A enters from input port R, passes through mode converter MO (being the total reflection state) successively, with the Michelson interferometer of time delay shutter, wherein through fixed mirror corner cube mirror M ₈A branch of light as surveying light E (t), another is restrainted through removable corner cube mirror M ₉Introduce a relative time and postpone τ as switch light signal E (t-τ), two-beam line focus lens L3 is converged in the frequency-doubling crystal (BBO), thereby produce and frequency light Esig (t, τ), this is to detect needed flashlight, it should satisfy relation: Esig (t, τ) ∝ E (t) (t-τ) as can be known according to the nonlinear optics principle.Owing to also produce other light of different directions simultaneously in the nonlinear medium, therefore, utilize the described spatial filtering aperture GQ unwanted parasitic light of filtering to greatest extent, and with flashlight Esig (t, τ) be directly incident on spectrometer GPY (this moment, gain-selector switch should be in the total transmissivity state), and by the measured image (SHG-FROG trace) of gamma camera CCD record, image and related data are input to computing machine DN processing, utilize the interative computation program, just can obtain the amplitude (pulsewidth) of tested femto-second laser pulse, phase place, information such as spectral bandwidth, and can draw the waveform image.Obviously, this testing process is the described second harmonic frequency resolution optical of Fig. 9 shoulder rotation (SHG-FROG method).

2, " state model of warbling " (this moment, mode converter was a completely reflecting mirror, gain-selector switch is in the total reflection state) time, after mode converter is incided in the measured laser pulse, be totally reflected to the beam splitter in the Michelson interferometer of time delay shutter and be divided into two bundles, wherein a branch of warp is with the reflected light conduct " fixed light " of the fixedly corner cube mirror of the Michelson interferometer of time delay shutter, with the reflected light conduct " removable light " of another Shu Jing with the corner cube mirror of removable (the starting its accurate slow-motion retaining) of the Michelson interferometer of time delay shutter, under computer control, select minimum step, this " removable light " is scanned above-mentioned " fixed light ", and make the stepper motor revolution further gather data.Therefore, can access the distinguishable second harmonic auto-correlation of interference fringe plane curve figure, related data just can obtain intuitively contained size and the positive negative information of warbling of femto-second laser pulse by Computer Processing, reaches as effect as described in the Chinese patent (ZL200420110194.2).

3, when " instant phase pattern ", tested femto-second laser pulse A enters from input port R, pass through mode converter MO successively, mode converter was half-reflection and half-transmission and penetrated state this moment, make the measured laser pulse be divided into transmitted light and reflected light: the light of institute's transmission is by the transmission plane of one side transmission another side catoptron, incide spectrum phase modulator GT (stretcher) and give linear just warbling and modulated, be back to the reflecting surface of one side transmission another side catoptron then along former road, and reflex to completely reflecting mirror M ₁₂, reflex to condenser lens L3 again.On the other hand, in the measured laser pulse that mode converter reflected, pass Michelson interferometer, condenser lens, frequency-doubling crystal, spatial filtering aperture, gain-selector switch (gain-selector switch is the total transmissivity state) and spectrometer successively with the time delay shutter.The measured laser pulse is by the Michelson interferometer with the time delay shutter, produce the mirror image pulsed light beam with relative delay τ: E (t) and E (t-τ), and with aforementioned by having of one side transmission another side mirror reflects be endowed the linear light beam E ' that is just warbling (t) parallel incide condenser lens enter take place in the frequency-doubling crystal BBO relevant and frequently, because time delay τ and the existence of warbling, make the mirror image pulsed light beam be endowed linear light beam of just warbling on different frequency and frequently, therefore produce a frequency difference, this frequency difference is called as the spectral tailoring amount, represents with Ω.Light beam process spatial filtering aperture, gain-selector switch (this moment, gain-selector switch was the total transmissivity state) with behind the frequency enter spectrometer and write down the relevant interference fringe image of its spectrum by the CCD gamma camera, and its mathematic(al) representation is:

$D(\mathrm{\ω},\mathrm{\τ})={\left|\tilde{E}({\mathrm{\ω}}_C-\mathrm{\Ω})\right|}^2+{\left|\tilde{E}\left({\mathrm{\ω}}_C\right)\right|}^2+2\left|\tilde{E}({\mathrm{\ω}}_C-\mathrm{\Ω})\right|\left|\tilde{E}\left({\mathrm{\ω}}_C\right)\right|\×\mathrm{COS}[\mathrm{\θ}\left({\mathrm{\ω}}_C\right)-\mathrm{\ω\τ}]$

Wherein, D (ω, τ) for take the photograph the expression formula of interference fringe image;

And

It is the right frequency-domain expression of input pulse; Ω is the spectral tailoring amount, and

τ is time delay, It is the 2nd order chromatic dispersion of spectrum phase modulator; ω _cAnd ω _c-Ω is respectively the centre frequency of two pulses behind spectral tailoring.

The interference fringe image that above-mentioned spectrum is relevant (or claiming SPIDER trace data) is imported in the computing machine, and handles with the inversion algorithm of SPIDER, just can obtain the phase information of femto-second laser pulse.Because computing is simple, quick, thereby can obtain the instant phase information of measured laser pulse.

Obviously, this testing process is the relevant direct electric field reconstruct method (SPIDER method) in the described spectrum of Figure 10 position.

4, when " comparison pattern ", tested femto-second laser pulse A enters from input port R, this moment, mode converter rotated by given pace (measuring the needed separately time according to SHG-FROG method and SPIDER method that " perfect information pattern " is corresponding with " instant phase pattern "), make that the measured laser pulse is well-regulated is back and forth penetrated change (this moment, gain-selector switch was the total transmissivity state) by optical frames total reflection and half-reflection and half-transmission, then can measure same tested femto-second laser pulse by enough two kinds of distinct methods (FROG method and SPIDER method), compare and measure the result, and provide its mean value, thereby further improved the degree of accuracy of measuring.

Original state is provided with and adjusts:

(1) when initial measurement, adjust the correct incident angle that the measured laser pulse enters input port R, make the corresponding pilot lamp of observation display window of femtosecond laser camera bright.Make mode converter be in " perfect information pattern " (being the total reflection state) by computing machine, gain-selector switch is enabled half-reflection and half-transmission and is penetrated state, enable and interfere autocorrelation receiver SHG, and the fast moving retaining whole process of opening the Michelson interferometer of having the time delay shutter moves back and forth once, the measured laser pulse is via the light path of " perfect information pattern " as previously mentioned, can observe the maximal value of measured laser pulse autocorrelation signal on the observation display screen by femtosecond laser camera, thereby can determine that SHG-FROG measures needed optimal delay moment τ value and deposits computing machine in, is carried out by the time delay shutter when to be measured.Simultaneously, can measure the center carrier frequencies and the spectral bandwidth of measured laser pulse by spectrometer, photodetector, it is stand-by to deposit these parameters in computing machine.

(2) also needing to make mode converter be in " instant phase pattern " (be half-reflection and half-transmission and penetrate state), gain-selector switch by computing machine enables half-reflection and half-transmission and penetrates state, enables and interfere autocorrelation receiver SHG simultaneously, the measured laser pulse is via the light path of " instant phase pattern " as previously mentioned, and the fast moving retaining whole process of opening with the Michelson interferometer of time delay shutter moves back and forth, and adjusts the removable completely reflecting mirror M in the spectrum phase modulator (stretcher) simultaneously ₁₁With the distance (can change the value of its 2nd order chromatic dispersion amount) of grating, and can observe on the observation display screen by femtosecond laser camera measured laser pulse coherence light intensity to different delay time T and

Situation of change, thereby can determine that the SPIDER method measures the needed optimal delay span of τ and Ω constantly, deposit computing machine in and carry out by the time delay shutter when to be measured.

Claims (5)

1, femtosecond laser camera, it is characterized in that this camera has a laser input port R, laser pulse direction along this port is disposed with mode converter MO, one side transmission another side catoptron BF and spectrum phase modulator GT, and the mirror M of a transmission laser pulse is set between one side transmission another side catoptron BF institute's laser light reflected pulse direction and condenser lens L3 ₁₂, transport to spectrum phase modulator GT and carry out frequency and cut out so that make this road laser pulse pass mode converter MO, one side transmission another side catoptron BF earlier, be back to one side transmission another side catoptron BF then along former road and reflex to condenser lens L3; Again at the Michelson interferometer of mode converter MO institute laser light reflected pulse direction setting with the time delay shutter, and set gradually condenser lens L3 in the laser pulse direction that Michelson interferometer is exported, frequency-doubling crystal BBO, spatial filtering aperture GQ, gain-selector switch MG and spectrometer GPY, and interference autocorrelation receiver SHG is set in gain-selector switch MG institute laser light reflected pulse direction, also be furnished with computing machine DN and gamma camera CCD in addition, so that make the pulse of another route pattern converter MO laser light reflected pass Michelson interferometer earlier, and after merging, condenser lens L3 enters that frequency-doubling crystal BBO carries out and frequently from parallel together being input to of Michelson interferometer output back and aforesaid road laser pulse that is reflected by one side transmission another side catoptron BF; Through restrainting laser pulses by being divided into two behind spatial filtering aperture GQ, the gain-selector switch MG again with laser pulse frequently, the beam of laser pulse is passed gain-selector switch and is entered spectrometer GPY, by CCD gamma camera shooting and deliver to computing machine DN and handle pictorial data, another bundle laser pulse is reflexed to interfere by gain-selector switch and outputs signal to computing machine DN behind the autocorrelation receiver SHG and handle; Be provided with the optical frames of the circle that can rotate around the center of circle among the described mode converter MO, wherein hemicycle is made completely reflecting mirror (2), hemicycle is made half-reflecting half mirror (1) in addition, this mirror is by precision electric motor (3) drive and by computer control, so that the detected state of femtosecond laser camera is in perfect information pattern, instant phase pattern, warble state model or comparison pattern.

2, femtosecond laser camera according to claim 1, it is characterized in that being provided with among the described gain-selector switch MG optical frames of the circle that can rotate around the center of circle, wherein 1/3 circle is made completely reflecting mirror (22), 1/3 circle is made half-reflecting half mirror (21), 1/3 circle is full impregnated mirror (23), and this mirror is by the precision electric motor drive and by computer control.

3, femtosecond laser camera according to claim 1, it is characterized in that described time delay shutter comprises accurate screw rod leading screw (15), stepper motor (14), precise displacement sensor (11) and the interlock circuit that is arranged in the oil-filled inner chamber (13), and be connected control with computing machine DN, also comprise the movable corner cube mirror M in the Michelson interferometer ₉

4,, it is characterized in that described spatial filtering aperture GQ is a center pit area continuously controllable aperture, fixes with optics multidimensional adjusting bracket according to claim 1 or 2 or 3 described femtosecond laser cameras.

5, femtosecond laser camera according to claim 4 is characterized in that described spectrum phase modulator GT comprises the grating G of mutual formation certain angle, corner cube mirror M ₁₀With removable mirror M ₁₁

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