CN2630843Y - Super rapid process detecting device - Google Patents

Abstract

An ultra-fast process detection facility is provided, the composition and the position relation is that: a light source is divided into a transmitted pumping light and a reflected probe light by a first spectroscope, the pumping light is reflected by a first whole reflector and passes a first aggregating lens then radiates vertically on the sample being measured after passing a pulse broadening device and a first delay light path system, the probe light is focused on the sample by a second aggregating lens after passing a second whole reflector and a third whole reflector, the probe light is provided with a first detector on the relative sample reflected light path, a second detector is arranged in the transmissive direction of the probe light passing the sample, the pulse width of the pumping light is broadened to plural times, plural tens of times or plural hundreds of times of the probe light pulse width by the pulse broadening device, the probe light and the pumping light share focus. The utility model mainly used in measuring the ultra-fast process of the bulk material and the nano-structure material such as the semiconductor and the transparent medium under the effect of the ultra-short pulse laser, especially suits to measure the excitation process.

Description

The sniffer of ultrafast process

Technical field:

The utility model relates to the ultrafast process of material and measures, it is the sniffer of ultrafast process under a kind of ultra-short pulse laser effect, mainly be applicable to and block materials and the ultrafast process of nano structural material under the ultra-short pulse laser effect such as measuring semiconductor and transparent medium especially be applicable to measurement excitation process.

Background technology:

Pumping-probe unit is widely used in measuring the ultrafast process of semiconductor body material under femtosecond, picosecond laser irradiation.Middle nineteen nineties, pumping-probe unit begins to be used to measure the ultrafast process of transparent medium block materials and nano structural material again.It mainly passes through the temporal evolution of reflectivity, transmissivity and the luminescent spectrum of measurement material, the ultrafast nonlinear optical response of research material, and electronics, lattice excites and relaxation mechanism in the exploration material.

The ultimate principle of studying excited state electron number density evolution by the variation of measurement of reflectivity is the dispersion theory of dielectric material.The reflection coefficient of material and the pass of refraction coefficient are

$r_s=\frac{{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1\cos \mathrm{\&phi;}-{(N_2^2-{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2\mathrm{si}{n}^2\mathrm{\&phi;})}^{1/2}}{{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1\cos \mathrm{\&phi;}+{(N_2^2-{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2\mathrm{si}{n}^2\mathrm{\&phi;})}^{1/2}}---\left(1\right)$

$r_p=\frac{N_2^2\cos \mathrm{\&phi;}-{(N_2^2{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2-{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^4{\sin }^2\mathrm{\&phi;})}^{1/2}}{N_2^2\cos \mathrm{\&phi;}+{(N_2^2{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2-{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="Y0322859000081.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^4{\sin }^2\mathrm{\&phi;})}^{1/2}}$

Here r _sAnd r _pBe respectively S ripple and P wave reflection coefficient, n ₁And N ₂Be respectively the complex index of refraction of incident medium and sample,  is an incident angle.

The real part ε of sample specific inductive capacity ₁With imaginary part ε ₂With the pass of sample refractive index n and extinction coefficient k be

ε ₁＝n ²-k ² (2)

ε ₂＝2nk

The change amount of specific inductive capacity and the pass of conduction band electron number density are

${\mathrm{\&Delta;\&epsiv;}}_1=-\frac{n_e{e}^2{\mathrm{\&tau;}}^2}{m^{*}(1+{\mathrm{\&omega;}}^2{\mathrm{\&tau;}}^2){\mathrm{\&epsiv;}}_0}---\left(3\right)$

${\mathrm{\&Delta;\&epsiv;}}_2=-\left(\frac{1}{\mathrm{\&omega;\&tau;}}\right)\frac{n_e{e}^2{\mathrm{\&tau;}}^2}{m^{*}(1+{\mathrm{\&omega;}}^2{\mathrm{\&tau;}}^2){\mathrm{\&epsiv;}}_0}$

Here n _eBe the number density of excited state electronics, m ^*Be its effective mass, e is an electron charge, and τ is the time constant of electronics-electronics, electronics-lattice point collision, ε ₀Be permittivity of vacuum, ω is the angular frequency of laser.

According to formula (1～3),, just can record near the temporal evolution of the excited state electron number density of sample surfaces as long as record the variation of S ripple and P wave reflection rate.Utilize the variation and the characteristic that excited state electron number density is directly proportional of transmissivity, can record the average number density of conduction band electron in the material and life-span etc.

Under the ultra-short pulse laser effect, the dynamic behavior of material can be divided into excitation process and the relaxation process of laser pulse after the past in the laser irradiation process.Compare with relaxation process, the excitation process of material is even more important, because it is not only the part of the whole dynamic process of material, also directly influences the relaxation process of back simultaneously, is the basis of the ultrafast dynamic behavior of research material.The excitation process of the excitation process of material, especially transparent material and wide band gap semiconducter and nano structural material is the non-linear process of a complexity under the femtosecond laser effect.The ground state electronics excited mechanism such as multiphoton excitation and collision excitation.So measuring the excitation process of material under the ultra-short pulse laser effect is extremely important, an anxious to be solved problem.

Formerly in the technology (referring to document: A.Othonos, Journal of Applied Physics, Vol.83, P 1789,1998; T.Kom, A.Franke-Wiekhorst, et.al., Journal of Applied Physics, Vol.91, P 2333,2002) light source (being generally the femtosecond pulse bundle) is divided into pump light and probe light with spectroscope, through the time-delay light path that two-beam is confocal on sample then.Because formerly the pulse width of pump light and probe light is identical in the technology, thus in the time interval of pump light irradiation material, utilize probe light can only record a distinguishable reflectivity of time (or transmissivity), can not detailed measurements excitation process.

Summary of the invention:

The technical problems to be solved in the utility model is to overcome the deficiency in the above-mentioned technology formerly, a kind of ultrafast process sniffer is provided, it can not only measure block materials and the relaxation processes of nano structural material under the ultra-short pulse laser effect such as semiconductor and transparent medium, especially can also at length measure excitation process.

The basic design (as shown in Figure 1) of the utility model technical solution problem is: at first utilize spectroscope that light source is divided into pump light and probe light.The pulse width of probe light remains unchanged.Utilize dispersion element with the pump light pulse width from tens femtosecond broadenings to hundreds of femtosecond, several psecs etc.Like this, in pump light acts on time interval of material, can record several, tens even distinguishable reflectivity of a hundreds of time (or transmissivity), thereby can at length measure the excitation process of material.

The concrete technical solution (seeing also shown in Figure 2) of the utility model is as follows:

A kind of sniffer of ultrafast process, its formation and position relation is as follows: light source (1) is divided into the pump light of transmission and the probe light of reflection through first spectroscope (2).This pump light through the pulse strenching device (3) and the first time-delay light path system (4) after, by first be all-trans that light microscopic (5) reflects and through first plus lens (7) vertical irradiation on sample (11).This probe light is all-trans and is focused on the sample (11) by second plus lens (13) behind the light microscopic (14) through second light microscopic (15) and the 3rd that is all-trans.This probe light is provided with first detector (10) with respect to the reflected light path of sample (11), is provided with second detector (12) in the transmission direction of this probe light by sample (11).The pulse width of described pump light is broadened through pulse stretcher spare (3) to be several times, tens times or hundred times of probe optical pulse width.Described probe light and pump light are confocal.

Be positioned at first spectroscope (2) and second in the described probe light path and be all-trans and be provided with second spectroscope (17) between the light microscopic (15), this second spectroscope (17) is divided into first probe light of reflection and the second probe light of transmission with probe light.This first probe light shines the 4th light microscopic (6) that is all-trans through the second time-delay light path system (16), incides on the sample (11) with less incident angle through the 3rd plus lens (8).The first probe light is provided with second detector (9) with respect to the reflected light path of sample (11); The second probe light then shines sample (11) along former probe light path, and is surveyed by first, second detector (10,12).

Described pulse strenching device (3) can by grating pair, prism to or these dispersion elements of glass bar of high index of refraction form.

Described detector can be photomultiplier, spectrometer or energy meter.

Described Pu optical pulse broadening device can by grating pair, prism to or the chromatic dispersion elements such as glass bar of high index of refraction form.A Gauss pulse through the forward and backward pulse width ratio of dispersion element is

Here t _mAnd t _OutBe respectively the forward and backward pulse width of laser pulse process dispersion element, is the position phase of laser.Here

ω is the angular frequency of laser.

Adopt the grating of two laid parallels can stretched pulse, its GVD (Group Velocity Dispersion) be

${\cos }^2\mathrm{\&beta;}=1-{(\frac{2\mathrm{\&pi;c}}{\mathrm{\&omega;d}}-\sin \mathrm{\&alpha;})}^2$

Here d is the distance between centers of tracks of grating, and b is the vertical range of two blocks of gratings, and α and β are respectively incident angle and angle of diffraction, and c is the light velocity in the vacuum.

If adopt parallel prism to stretched pulse, its GVD (Group Velocity Dispersion) is

Here L is two distances between the prism, and δ is the deflection angle of light, ω ₀It is the central angle frequency of laser beam.

If the glass bar that adopts high index of refraction is as dispersion element, then its GVD (Group Velocity Dispersion) is

Here n is the material refractive index, and g is the length of glass bar, and λ is an optical maser wavelength.

Utilize formula (4-8) can calculate the width of pump light through the dispersion element afterpulse of different parameters, in conjunction with concrete measured object, the user can select dispersion element.

Compare with technology formerly, the utility model has the advantages that: pumping-probe unit of the present utility model can be with the pulse width of pump light according to user's needs broadening easily; Do not reduce under the situation of temporal resolution in assurance, the scope that the utility model device is used is more extensive.It can not only measure block materials and the relaxation processes of nano structural material under the ultra-short pulse laser effect such as semiconductor and transparent medium, particularly can also at length measure excitation process.

Description of drawings

Fig. 1 is the synoptic diagram of pump light-probe light relative delay and pump light pulse width broadening.

Fig. 2 is the structural representation of the utility model ultrafast process sniffer most preferred embodiment.

Fig. 3 is the synoptic diagram that S ripple and P ripple probe light reflectivity change with the pump light irradiation time.

Embodiment

See also Fig. 1 and Fig. 2 earlier.Fig. 1 is the synoptic diagram of pump light-probe light relative delay.Time is t, probe optical pulse 01, pump light pulse 02 in the technology formerly, the pump light pulse 03 of the utility model device.Formerly the pulse width of pump light and probe light is identical in the technology, can not carefully measure the excitation process of material.As seen from the figure, pump light pulse 03 of the present utility model is several times of probe optical pulse 01.We can also utilize dispersion element that the pump light pulse width is become tens times at broadening, even hundred times is in the pulse width of probe light.

Fig. 2 is the structural representation of the utility model ultrafast process sniffer most preferred embodiment.Its structure is as follows: light source 1 (being generally femto-second laser pulse) is divided into a branch of pump light (shown in the thick dotted line) of transmission and the probe light (shown in the fine line) of reflection through first spectroscope 2.Pump light through the pulse strenching device 3 and the first time-delay light path system 4 after, by first be all-trans light microscopic 5 reflections and through first plus lens, 7 vertical irradiations to sample 11.Probe light is divided into first probe light of reflection and the second probe light of transmission through second spectroscope 17.The first probe light shines second light microscopic 6 that is all-trans behind the light path system 16 through second time-delay, incides on the sample 11 with less angle through second plus lens 8.The second probe light is all-trans and is focused on the sample 11 by the 3rd plus lens 13 behind the light microscopic 14 through the 3rd light microscopic 15 and the 4th that is all-trans, and incident angle is general bigger.Two bundle probe light and pump light are confocal.Make two bundle probe light arrive sample simultaneously by regulating the second time-delay light path system 16.By regulating the relative time that the first time-delay light path system 4 changes pump light and probe light, utilize first detector 9 and second detector 10 to measure the temporal evolution of the first probe light and the second probe reflection of light rate respectively, the evolution that utilizes the 3rd detector 12 to measure the first probe light transmission.Described detector can be a photomultiplier.

The use of the utility model device illustrates as follows:

At first utilize autocorrelation function analyzer measurement two bundle probe light to arrive the mistimings of sample surfaces,, made for two bundle probe light whiles, confocal in sample surfaces by regulating the second time-delay light path system 16 (Fig. 2).Through pulse strenching device 3 (Fig. 2), can with autocorrelation function analyzer measure earlier by the pulse width behind the broadening for pump light.The pump light vertical irradiation is to sample surfaces, and confocal with probe light.The focal spot of probe light should be less than pump light, and this can realize by utilizing short lens of focal length or parabolic mirror.By regulating the relative time that the first time-delay light path system 4 (Fig. 2) changes pump light-probe light, utilize the variation of detector 9,10,12 measuring probe reflection of light rates and transmissivity.According to formula (1-3), the evolution of excited state electron number density in the research material discloses the physical mechanism that material excites.For the variation that makes the reflectivity that detects reflects the evolution of excited state electron number density in the material more delicately, can utilize polaroid to change the polarization direction of light beam, making the first probe light is the S ripple, and with less angle incident (being generally less than 20 degree).The second probe light is the P ripple, with near brewster angle incidence.

Titanium with 800nm, 40fs: sapphire laser irradiation quartz glass is an example, provides concrete scheme and the notional result of utilizing pumping of the present utility model-probe unit to measure material excitation process.Absorb processes such as the speed of laser energy or impact ionization in order to study under the femtosecond laser effect conduction band electron in the transparent medium, the pump light pulse width answers broadening to 500-800fs, so both can keep the interactional essential characteristic of femtosecond laser and material, again much larger than the pulse width of probe light, thereby can measure excitation process in more detail.At this moment, select the glass bar broadening pump light pulse easily of high index of refraction.The result who utilizes autocorrelation function analyzer to measure shows, is that the glass bar of ZF7 can be the laser pulse stretching of 40 femtoseconds, wavelength 800nm to the 500-800 femtosecond with long 15-20mm, model, and the while keep the Gaussian waveform of pulse again preferably.

The first probe light (S ripple) is with 15 ° angle incident, and the second probe light (P ripple) is with 55 ° angle incident.Pump light pulse width broadening is to 800fs, and the focus strength of sample surfaces pump light is adjusted to 2.6J/cm ²The notional result that two bundle probe reflection of light rates change with the pump light irradiation time as shown in Figure 3, the peak value with the pump light pulse arrives sample surfaces as time zero here.When pump light irradiation time during near 400 femtoseconds, S ripple probe reflection of light rate (shown in Fig. 3 round dot) descends and is close to zero since 3.7%, rises rapidly then, at last near 50%.P ripple probe reflection of light rate (shown in Fig. 3 diamond point) also begins to rise and arrive about 40% after the pump light irradiation time surpasses 400 femtoseconds.Here considered that conduction band electron absorbs the influence that laser energy causes impact ionization.When not considering impact ionization, S ripple and P wave reflection rate change hardly (respectively shown in dotted line and solid line among Fig. 3).Utilize device of the present utility model,, can study the evolution of conduction band electron number density, and then disclose the light absorption of conduction band electron and the physical mechanism of impact ionization by measuring the variation of S ripple and P ripple probe light reflectivity.

Claims (4)

1. the sniffer of a ultrafast process, it is characterized in that its formation and position relation is as follows: light source (1) is divided into the pump light of transmission and the probe light of reflection through first spectroscope (2), this pump light is delayed time through pulse strenching device (3) and first behind the light path system (4), by first be all-trans light microscopic (5) reflection and through first plus lens (7) vertical irradiation on sample (11), this probe light is all-trans and is focused on the sample (11) by second plus lens (13) behind the light microscopic (14) through second light microscopic (15) and the 3rd that is all-trans, this probe light is provided with first detector (10) with respect to the reflected light path of sample (11), be provided with second detector (12) in the transmission direction of this probe light by sample (11), the pulse width of described pump light is broadened through pulse stretcher spare (3) to be several times of probe optical pulse width, tens times or hundred times, described probe light and pump light are confocal.

2. ultrafast process sniffer according to claim 1, it is characterized in that it also is positioned at first spectroscope (2) and second and is all-trans and is provided with second spectroscope (17) between the light microscopic (15) in described probe light path, this second spectroscope (17) is divided into first probe light of reflection and the second probe light of transmission with probe light, this first probe light shines the 4th light microscopic (6) that is all-trans through the second time-delay light path system (16), incide on the sample (11) with less incident angle through the 3rd plus lens (8), the first probe light is provided with second detector (9) with respect to the reflected light path of sample (11), the second probe light then shines sample (11) along former probe light path, and by first, second detector (10,12) survey.

3. ultrafast process sniffer according to claim 1 and 2, it is characterized in that described pulse strenching device (3) can by grating pair, prism to or these dispersion elements of glass bar of high index of refraction form.

4. ultrafast process sniffer according to claim 3 is characterized in that described detector can be photomultiplier, spectrometer or energy meter.

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