CN1693861A - Measuring device using supershort pulse frequency resolution optical switch method - Google Patents

Abstract

The invention relates to a measuring device using ultrashort impulse frequency distinguish optical switch method that includes beam separator, micro-checker controlled by computer, lens, non-linear crystal, diaphragm, and spectroscopic instrument. The feature is that the beam separator is made up of the first reflecting type Daman grating and the second reflecting Daman grating and the third reflecting Daman grating. The second reflecting Daman grating is set on the computer controlled micro-checker. The invention is tightly structure and easy to manufacture.

Description

Measuring device using supershort pulse frequency resolution optical switch method

Technical field

The present invention relates to ultrashort laser pulse, particularly a kind of measuring device using supershort pulse frequency resolution optical switch method, it is the ultrashort pulse measuring device of the single-shot frequency resolution optical shoulder rotation of a kind of employing reflective dammann (Dammann) grating, this device is double-deck three optical grating constructions, and one of them grating is as transfer arm.

Background technology

Ultrashort pulse femtosecond (fs=10 particularly since nineteen nineties ^-15Second) laser technology has obtained development fast, because femto-second laser pulse has the ultrashort characteristic of time domain, can carry out the research of ultrafast phenomena to fields such as physics, chemistry, biology, medical science.Simultaneously, femto-second laser pulse also has high peak power, is the strong instrument that carries out various non-linear phenomena researchs.

The research of various phenomenons realizes by the femtosecond pulse measuring technique under the femto-second laser pulse effect, obtains the physical essence of femtosecond dynamic system response by the measurement to the characteristics such as time domain, frequency domain and transmission of femtosecond light.Simultaneously, the development of measuring technique also has huge impetus to the development of femtosecond laser technology itself, and the laser pulse that produces the shorter duration is had huge directive function.

The femto-second laser pulse measurement has a variety of methods, frequency resolution optical shoulder rotation (frequency-resolved optical gating wherein, FROG) [referring to technology 1 " Frequency-Resolved optical Gating:The Measurement ofUltrashort Laser Pulses " Rick Trebino formerly, 2002 Kluwer AcademicPublishers] with relevant electric field reconstruct method (the spectral phaseinterferometry for direct electric-field reconstruction in spectrum position, SPIDER) [referring to technology 2 " Spectral phase interferometryfor directelectric-field reconstructionof ultrashort optical pulses " C.Iaconis formerly, A.Walmsley, Optics Letters, Vol.23 Issue 10 1998] all be the two kinds of more methods that adopt at present.

Frequency resolution optical shoulder rotation measurement mechanism basic structure is that femtosecond pulse is made it to be divided into two-beam by semi-transparent semi-reflecting beam splitter, and a branch of light is as direct impulse, and another Shu Guang is as switching pulse.Focus on two beam pulse light on the nonlinear crystal at a certain angle then, produce frequency inverted, change the light path of switching pulse light and utilize the frequency inverted light of spectrometer measurement correspondence, obtain the two-dimensional map (FROG Trace) of intensity with respect to time and frequency, the amplitude that collection of illustrative plates using iterative algorithm [participating in technology 1 formerly] is obtained femtosecond pulse and position are mutually.

Fig. 1 is the standard measuring equipment of frequency resolution optical shoulder rotation, and this device has adopted semi-transparent semi-reflecting beam splitter 1.The particularly very short pulse of femto-second laser pulse has very wide frequency spectrum, and therefore desirable beam splitter should have following character:

1. the reflectance coating of beam splitter has smooth reflectivity to wide spectrum.

2. beam splitter is as far as possible little to the time domain broadening of transmitted light, absorbs as far as possible little.

3. the reflectivity of beam splitter is irrelevant with the polarization of incident light state.

But in fact present beam splitter is difficult to reach above-mentioned requirements, for example, and for the following ultrashort pulse of 20 femtoseconds, in order to reduce time domain broadening to transmitted light, require reflecting optics thickness to be no more than 50 microns, and will guarantee surface smoothness and substrate intensity, this is more unmanageable.In addition, the semi-transparent semi-reflecting rete with wide spectrum also is difficult to be coated with, and cost is also very high.

Frequency resolution optical shoulder rotation measuring method need guarantee that two pulses have identical light path in addition, and the catoptron of Shi Yonging is more as seen from Figure 1, and this has also increased the difficulty that light path is regulated.

Summary of the invention

The objective of the invention is to overcome the shortcoming of above-mentioned prior art, a kind of measuring device using supershort pulse frequency resolution optical switch method is provided, should have and to eliminate the broadening of hosqt media, easy to process, compact conformation, the advantage that light path is easy to adjust and cost is low femtosecond pulse.

Technical solution of the present invention is as follows:

A kind of measuring device using supershort pulse frequency resolution optical switch method, comprise beam splitter, computer-controlled micropositioner, lens, nonlinear crystal, diaphragm and spectrometer, it is characterized in that described beam splitter is by the one 1 * 2 reflective dammann grating, the 21 * 2 reflective dammann grating and the 31 * 2 reflective dammann grating stereoscopic configurations and the reflective dammann grating beam splitter that constitutes, described the 21 * 2 reflective dammann grating places on the computer-controlled micropositioner, its position relation is: when a branch of femtosecond pulse light in perpendicular and to incide the cycle with a low-angle be d, the degree of depth is λ _cOn/4 first reflective 1 * 2 Darman raster, in surface level, be divided into-1 grade of P light beam and+1 grade of G bundle light, this two-beam is placed on distance L place, back respectively and at conplane second reflective 1 * 2 Darman raster and three-mirror reflective 1 * 2 Darman raster institute diffraction, produce the P-1 level again respectively, P+1 level two-beam and G-1 level, G+1 level two-beam, wherein the P+1 level light beam of second reflective 1 * 2 Darman raster diffraction is covered by first baffle plate, the G-1 level light of three-mirror reflective 1 * 2 Darman raster institute diffraction is covered by second baffle, and G light+1 of the P-1 level light beam of second reflective 1 * 2 Darman raster diffraction and three-mirror reflective 1 * 2 Darman raster institute diffraction grade is incided lens abreast, converge at nonlinear crystal, received by spectrometer by diaphragm.

Described low-angle is less than 2 °.

Described second reflective 1 * 2 Darman raster and three-mirror reflective 1 * 2 Darman raster and the distance L of first reflective 1 * 2 Darman raster should guarantee by first reflective 1 * 2 Darman raster produce+1 grade of light can spatially separate with-1 grade of light.

Technique effect of the present invention is as follows:

1, the core of apparatus of the present invention is to adopt three Darman rasters, is easy to realize the aplanatism of pulse, has compact conformation, the advantage that light path is easy to adjust.

2, owing to adopt reflective dammann grating to replace beam splitter, can eliminate the broadening of beam splitter hosqt media, because the manufacturing technology of Darman raster and microelectronic processing technique compatibility mutually, have easy processing, advantage that cost is low femtosecond pulse.

Description of drawings

Fig. 1: the measuring device using supershort pulse frequency resolution optical switch method structural representation of existing standard.

Fig. 2 is a measuring device using supershort pulse frequency resolution optical switch method structure schematic top plan view of the present invention.

Fig. 3 shows side view for Fig. 2 measurement mechanism.

Fig. 4: the collection of illustrative plates that utilizes measuring device using supershort pulse frequency resolution optical switch method of the present invention to measure.

Fig. 5: the collection of illustrative plates that utilizes measuring device using supershort pulse frequency resolution optical switch method to measure.

Fig. 6: the amplitude of the pulse that calculates according to collection of illustrative plates 2 and 3 and position are mutually.

Scheme wherein: the 1-beam splitter; The 2-micropositioner; 3-rigging-angle cone catoptron; 4 is the anti-mirror of rigging-angle cone; 5 is catoptron; 6 is lens; 7 is nonlinear crystal; 8 is diaphragm; 9 is spectrometer; 11-the one 1 * 2 reflective dammann grating; 12-the 21 * 2 reflective dammann grating; 13-the 31 * 2 reflective dammann grating; The computer-controlled micropositioner of 2-; 31-first shadow shield; 32-second shadow shield.

Embodiment

The invention will be further described below in conjunction with accompanying drawing.

See also Fig. 2 and Fig. 3 earlier, measuring device using supershort pulse frequency resolution optical switch method of the present invention, comprise beam splitter 1, computer-controlled micropositioner 2, lens 6, nonlinear crystal 7, diaphragm 8 and spectrometer 9, it is characterized in that described beam splitter 1 is by the one 1 * 2 reflective dammann grating 11, the 21 * 2 reflective dammann grating 12 and the 31 * 2 reflective dammann grating 13 stereoscopic configurations and the reflective dammann grating beam splitter that constitutes, described the 21 * 2 reflective dammann grating 12 places on the computer-controlled micropositioner 2, its position relation is: when a branch of femtosecond pulse light in perpendicular and to incide the cycle with a low-angle less than 2 ° be d, the degree of depth is λ _cOn/4 first reflective 1 * 2 Darman raster 11, in surface level, be divided into-1 grade of P light beam and+1 grade of G bundle light, this two-beam is placed on distance L place, back respectively and at conplane second reflective 1 * 2 Darman raster 12 and 13 diffraction of three-mirror reflective 1 * 2 Darman raster, produce the P-1 level again respectively, P+1 level two-beam and G-1 level, G+1 level two-beam, wherein the P+1 level light beam of second reflective 1 * 2 Darman raster, 12 diffraction is covered by first baffle plate 31, the G-1 level light of 13 diffraction of three-mirror reflective 1 * 2 Darman raster is covered by second baffle 32, and G light+1 of the P-1 level light beam of second reflective 1 * 2 Darman raster, 12 diffraction and 13 diffraction of three-mirror reflective 1 * 2 Darman raster grade is incided lens 6 abreast, converge at nonlinear crystal 7, received by spectrometer 9 by diaphragm 8.

Technique effect to apparatus of the present invention is analyzed as follows:

Darman raster is [referring to technology 3 " Numerical study of Dammann arrayilluminators " Changhe Zhou formerly, and Liren Liu Applied Optics, Vol.34, No.26 1995] be a kind of diffraction optical device, be widely used in matrix lamp at present.Position and position by the flex point in the control Darman raster one-period are worth the control that realizes incident beam mutually, and Darman raster can easily be beamed into a branch of incident light m * n (m, n are integer) bundle.

When a branch of centre wavelength is the laser vertical of λ when to incide aperture efficiency be 1: 2 the grating of reflective dammann, reflected light can be divided into the identical two-beam of intensity, and the angle of emergent light and grating normal is

θ＝sin ^-1(λ/d) (1)

Grating degree of depth h is relevant with catoptrical diffraction efficiency

$\mathrm{\&eta;}=I_{+1}=I_{-1}=I_0\frac{4}{{\mathrm{\&pi;}}^2}{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A20051002655500102.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\frac{\mathrm{\&phi;}}{2}---\left(2a\right)$

$\mathrm{\&phi;}=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}h---\left(2b\right)$

I wherein _{+ 1}, I _-1Be respectively+1 grade and-1 grade of catoptrical intensity I ₀Be the incident pulse light intensity, h is the degree of depth of grating.Can be drawn by formula 2 that every bundle reflected light has the highest diffraction efficiency 40.5% when the h=λ/4, total diffraction efficiency is 81%.

The vertical view of measuring device using supershort pulse frequency resolution optical switch method structural representation of the present invention and side view are respectively as Fig. 2, shown in Figure 3, and a branch of centre wavelength is λ _c, width is τ ₀Femtosecond pulse light the cycle of inciding is d with a low-angle (less than 2 degree) in perpendicular, the degree of depth is λ _cOn/4 first reflective 1 * 2 Darman raster 11, in surface level, be divided into-1 grade of P and+1 grade of G two-beam, this two-beam is placed on distance L place, back respectively and by at conplane second reflective 1 * 2 Darman raster 12 and 13 diffraction of three-mirror reflective 1 * 2 Darman raster, produce two-beam respectively, utilize first baffle plate 31 and second baffle 32 respectively with light beam P+1 grade of light,-1 grade of light of G covers, according to grating equation as can be known-1 grade of light of light beam P and G+1 only parallel and aplanatic.In addition according to [technology 4 Guowei Li formerly, Changhe Zhou, andEnwen Dai, " Splitting of femtosecond laser pulses by using aDammann grating and compensation gratings ", J.Opt.Soc.Am.A, 22 (2005)] can draw pulsed light through the pulse width behind the grating pair.

$\mathrm{\&tau;}=\sqrt{{\mathrm{\&tau;}}_0^2+\frac{{\left(2k{\mathrm{\&beta;}}^{2}L\right)}^2}{{\mathrm{\&tau;}}_0^2}}---\left(3\right)$

Wherein $\mathrm{\&beta;}={\mathrm{\&lambda;}}_{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002655500102.png"\; state="\{\{state\}\}">c</figure-callout>}}^2/\left(2\mathrm{\&pi;cd}\right),$ K=2 π/λ _c, c is the light velocity.

Darman raster 12 is fixed on the computer-controlled micropositioner 2, and micropositioner 2 can be regulated the position of second reflective 1 * 2 Darman raster 12, thereby can change the optical path difference of two pulses.Two-beam is focused in the nonlinear crystal 7 by lens 6 and produces flashlight, and flashlight is received by spectrometer 9 by shadow shield 8 and produces frequency discrimination, utilizes micropositioner 2 to change light path and realizes optical switch, can obtain the FROG collection of illustrative plates.

In sum, the present invention has realized the ultrashort pulse photo measure of total-reflection type with three reflection Darman rasters, thereby eliminated the influence of traditional saturating/reflecting light beam splitter paired pulses light, simultaneously the manufacturing technology of Darman raster is compatible mutually with microelectronic processing technique, so has easy processing, advantage that cost is low.

Utilize the second harmonic FROG method of the reflective dammann grating of cycle d=100 μ m surface gold-plating to measure.

Consider the ultrashort pulse central wavelength lambda _cThe situation of=818nm time domain width 77 femtoseconds.Can obtain according to formula (1), the catoptrical angle theta of two bundles is 1.4724 °, when the degree of depth of grating is λ/4=0.2045 μ m, and catoptrical centre wavelength diffraction efficiency maximum.Can obtain 77.004 femtoseconds according to formula (3) during L=300mm.Bbo crystal has very high conversion efficiency of second harmonic, can measure more weak femtosecond pulse light, so nonlinear crystal 7 adopts BBO as changing crystal on the frequency.Change light path and obtain the FROG collection of illustrative plates by computer-controlled micropositioner 2 with spectrometer 9 measurements and frequency light.As shown in Figure 4.Fig. 5 is the collection of illustrative plates that obtains with standard FROG measurement mechanism.Fig. 6 be the amplitude that utilizes the pulse that technology 1 formerly calculates according to collection of illustrative plates 4 and Fig. 5 with the position mutually.

Concrete experimental result is as follows:

Time domain full width at half maximum spectrum width error

Dammam FROG 77.3fs 19.54nm 0.00094

Standard FROG 77.1fs 19.42nm 0.00188

As can be seen at λ _c=818nm, Dammam FROG and standard FROG have very approaching measurement result in the spectrum width 20nm scope, proved the validity of this device in this spectral range, because the reflectivity of gold all has smooth reflectivity in very wide spectral range, therefore can guarantee that this device remains effective to other spectral ranges.

Claims (3)

1, a kind of measuring device using supershort pulse frequency resolution optical switch method, comprise beam splitter (1), computer-controlled micropositioner (2), lens (6), nonlinear crystal (7), diaphragm (8) and spectrometer (9), it is characterized in that described beam splitter (1) is by the one 1 * 2 reflective dammann grating (11), the 21 * 2 reflective dammann grating (12) and the 31 * 2 reflective dammann grating (13) stereoscopic configurations and the reflective dammann grating beam splitter that constitutes, described the 21 * 2 reflective dammann grating (12) places on the computer-controlled micropositioner (2), its position relation is: when a branch of femtosecond pulse light in perpendicular and to incide the cycle with a low-angle be d, the degree of depth is on first reflective 1 * 2 Darman raster (11) of λ c/4, in surface level, be divided into-1 grade of P light beam and+1 grade of G bundle light, this two-beam is placed on distance L place, back respectively and at conplane second reflective 1 * 2 Darman raster (12) and three-mirror reflective 1 * 2 Darman raster (13) institute diffraction, produce the P-1 level again respectively, P+1 level two-beam and G-1 level, G+1 level two-beam, wherein the P+1 level light beam of second reflective 1 * 2 Darman raster (12) diffraction is covered by first baffle plate (31), the G-1 level light of three-mirror reflective 1 * 2 Darman raster (13) institute diffraction is covered by second baffle (32), and G light+1 of the P-1 level light beam of second reflective 1 * 2 Darman raster (12) diffraction and three-mirror reflective 1 * 2 Darman raster (13) institute diffraction grade is incided lens (6) abreast, converge at nonlinear crystal (7), received by spectrometer (9) by diaphragm (8).

2, measuring device using supershort pulse frequency resolution optical switch method according to claim 1 is characterized in that described low-angle is less than 2 °.

3, measuring device using supershort pulse frequency resolution optical switch method according to claim 1, it is characterized in that described second reflective 1 * 2 Darman raster (12) and three-mirror reflective 1 * 2 Darman raster (13) and the distance L of first reflective 1 * 2 Darman raster (11) should guarantee by first reflective 1 * 2 Darman raster (11) produce+1 grade of light can spatially separate with-1 grade of light.

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