CN101871814A - Method for measuring pumping electrooptics of Terahertz impulse energy - Google Patents

Abstract

The invention belongs to the technical field of electrooptics, in particular to a method for measuring pumping electrooptics of Terahertz impulse energy. The method is characterized by comprising the following steps: firstly, acquiring Terahertz absolute electric field strength; then, collecting Terahertz light spot, and obtaining energy of Terahertz impulse through integral of the Terahertz light spot on certain area and impulse duration. The method solves the problem of energy measurement of Terahertz impulse to overcome the defect that the existing method can not directly measure the energy because of shortage of a direct Terahertz wave response element, provides an effectively technical proposal for Terahertz energy meter designing, and provides a reference calibrating method for high-power Terahertz radiation source study.

Description

The method for measuring pumping electrooptics of Terahertz impulse energy

Technical field

The present invention relates to field of photoelectric technology, be specifically related to a kind of method for measuring pumping electrooptics of Terahertz impulse energy.

Background technology

Tera-hertz spectra, imaging technique have obtained developing rapidly in recent years, only need know the relative electric field intensity of terahertz signal in these technology, so the measurement of the absolute electric field intensity of researchist's less relevance for a long time.In addition, up to the present, still lack the components and parts that terahertz pulse is directly responded in the practical experience of life, this also is a factor that causes directly measuring absolute electric field intensity of Terahertz and energy, also is to hinder the major reason that Terahertz Technology develops rapidly for a long time.

But along with the development and the application of Terahertz Technology, people recognize that the terahertz emission energy becomes the serious bottleneck of Terahertz Technology in application day by day.For the development that promotes the terahertz emission source and will develop faster and better and the Terahertz Technology that is about to grow up is applied in the practical experience of life, be necessary to study the method for demarcating or measuring the size of terahertz emission energy.

Summary of the invention

The object of the present invention is to provide a kind of method for measuring pumping electrooptics of Terahertz impulse energy, it can effectively measure the energy size of terahertz pulse, thereby has overcome the direct response element of current shortage THz wave and can't directly measure the problem of energy.

Realize the technical scheme of the object of the invention: a kind of method for measuring pumping electrooptics of Terahertz impulse energy may further comprise the steps:

(1) obtains exploring laser light spectrum: adopt single chirped pulse electro-optic detection method, regulate that angle becomes 45 degree between quarter-wave plate crystallographic axis and laser polarization direction, had respectively and the exploring laser light spectrum when not loading terahertz pulse;

(2) analyze the intensity in transmission of exploring laser light: according to obtain in the step (1) do not load terahertz pulse the time exploring laser light spectrum, analyze and survey optical transmission intensity when not loaded terahertz pulse:

$I_T^{\mathrm{THz}=0}=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="I"\; filenames="H2009101360094E0000021.png,H2009101360094E0000022.png"\; state="\{\{state\}\}">I</figure-callout>}}_0\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">T</figure-callout>}$ ①

Exploring laser light spectrum during according to the loading terahertz pulse that obtains in the step (1), analyze and survey optical transmission intensity when obtaining being loaded with terahertz pulse:

$I_T^{\mathrm{THz}\&NotEqual;0}=\frac{1}{2}(1+\sin {\mathrm{\&Gamma;}}_{\mathrm{THz}})I_0\&CenterDot;T$ ②

I in the formula ₀Be the light intensity of incident detecting light beam, T is the transfer coefficient of crystal and other optical elements, Г _THzFor loading the phase delay that terahertz pulse causes;

(3) the absolute electric field intensity of calculating terahertz pulse: 1., 2. obtain loading the phase delay that terahertz pulse causes according to formula:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\arcsin (\frac{I_T^{\mathrm{THz}\&NotEqual;0}}{I_T^{\mathrm{THz}=0}}-1)$ ③

Owing to for the zinc telluridse electro-optic crystal that is adopted in step (1) the electro-optic detection technology, have relational expression:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}{\mathrm{Ln}}^3{r}_{41}{E}_{\mathrm{THz}}$ ④

3., 4. combinatorial formula and is proofreaied and correct the reflection of terahertz pulse in conjunction with zinc telluridse electro-optic detection crystal and can be obtained the outer absolute electric field intensity of tested THz wave of plane of crystal and be:

$E_{\mathrm{THz}}=\frac{{\mathrm{\&Gamma;}}_{\mathrm{THz}}{\mathrm{\&lambda;}}_0}{2\mathrm{\&pi;}{\mathrm{Ln}}^3{r}_{41}}\&CenterDot;\frac{1}{1-{\mathrm{<figure-callout\; id="5"\; label="R\; THz"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{THz}}}$ ⑤

In the formula, λ ₀Centre wavelength for laser; L is the thickness of crystal; N is the refractive index of crystal to exploring laser light; r ₄₁Be the electrooptical coefficient of crystal,

Be the reflectance coefficient of Terahertz electric field at the electro-optic detection plane of crystal, wherein n _THzBe the refractive index of crystal to THz wave;

(4) gather the terahertz pulse hot spot, obtain terahertz pulse spot size size: the terahertz pulse hot spot is by off axis paraboloidal mirror THz wave to be converged on the zinc telluridse crystal, utilizes charge coupled array that the detection photoimaging is obtained by pumping detecting method and delustring technology then; Afterwards, by being carried out match on horizontal and vertical lines shape, the terahertz pulse hot spot obtains spot size;

(5) calculate the energy of terahertz pulse according to following formula:

$U_{\mathrm{THz}}={\mathrm{\&epsiv;}}_{0}c\underset{A,t}{\&Integral;\&Integral;}{E}_{\mathrm{THz}}^2\mathrm{<figure-callout\; id="6"\; label="dAdt"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">dAdt</figure-callout>}$ ⑥

In the formula, A is the terahertz pulse facula area, and t is the terahertz pulse duration, ε ₀Be permittivity of vacuum, c is the light velocity in the vacuum.

The method for measuring pumping electrooptics of aforesaid a kind of Terahertz impulse energy obtains the terahertz pulse hot spot and has adopted single chirped pulse electro-optic detection method and delustring technology in the step (4).

Effect of the present invention is: at first obtain the absolute electric field intensity of terahertz pulse, gather the hot spot of terahertz pulse then, by on the certain area of terahertz pulse hot spot and the integration on the duration of pulse obtain the energy of terahertz pulse, this method has solved the energy measurement problem of terahertz pulse, thereby overcome the direct response element of current shortage THz wave and can't directly measure the difficulty of energy, for the design of THz wave energy meter provides a kind of effective technology scheme, and provide a kind of benchmark calibration method for the research in high-power terahertz emission source.

Description of drawings

Fig. 1 adopts single chirped pulse electro-optic detection technology to survey the scheme synoptic diagram of the absolute electric field intensity of terahertz pulse among the embodiment;

Fig. 2 adopts single chirped pulse electro-optic detection technology to survey the scheme synoptic diagram of terahertz pulse spot size among the embodiment;

Exploring laser light spectrum when Fig. 3 loads the zinc telluridse crystal detection for the Terahertz electric field is arranged among the embodiment;

Exploring laser light spectrum when Fig. 4 loads the zinc telluridse crystal detection for there not being the Terahertz electric field among the embodiment.

Among the figure: 1 catoptron, 2 beam splitters, 3 light-balancing filters, 4 gratings, 5 off axis paraboloidal mirrors, 6 zinc telluridse crystal, 7 convex lens, 8 half-wave plates, 9 quarter-wave plates, 10 polarizing cubes, 11 photoconduction antennas, 12 spectrometers, 13 diaphragms, 14 charge-coupled image sensors.

Embodiment

Below in conjunction with drawings and Examples the present invention is further described.

In the experiment, adopting the centre wavelength of pumping laser is λ ₀=800nm, pulse width 60fs, repetition frequency 10Hz, the laser beam diameter is 4.5cm, the pulsed laser energy that is radiated on the terahertz light lead antenna is 6mJ.The method of utilizing the pumping electrooptics Detection Techniques to carry out the Terahertz impulse energy measurement may further comprise the steps:

(1) obtains exploring laser light spectrum: adopt single chirped pulse electro-optic detection scheme as shown in Figure 1, by adjusting the position of quarter-wave plate 9 and polarizing cube 10, make quarter-wave crystallographic axis and laser polarization direction in angle of 45 degrees, the detecting light beam of telling through beam splitter 2 passes through light-balancing filter 3, grating 4, off axis paraboloidal mirror 5, the zinc telluridse crystal 6, convex lens 7, half-wave plate 8, quarter-wave plate 9 is behind polarizing cube 10 elements such as grade, exploring laser light spectrum when spectrometer 12 measures respectively and do not have the Terahertz electric field to load the zinc telluridse crystal 6 is as Fig. 3, shown in Figure 4.

(2) analyze the intensity in transmission of exploring laser light: according to obtain in the step (1) do not have the Terahertz electric field to load the zinc telluridse crystal 6 time exploring laser light spectrum, analyze when not added carried terahertz signal, survey optical transmission intensity:

$I_T^{\mathrm{THz}=0}=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="I"\; filenames="H2009101360094E0000021.png,H2009101360094E0000022.png"\; state="\{\{state\}\}">I</figure-callout>}}_0\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">T</figure-callout>}$ ①

Exploring laser light spectrum when loading the zinc telluridse crystal 6 according to the Terahertz electric field that obtains in the step (1) is analyzed when obtaining being loaded with terahertz signal, surveys optical transmission intensity:

$I_T^{\mathrm{THz}\&NotEqual;0}=\frac{1}{2}(1+\sin {\mathrm{\&Gamma;}}_{\mathrm{THz}})I_0\&CenterDot;T$ ②

I in the formula ₀Be the light intensity of incident detecting light beam, T is the transfer coefficient of crystal and other optical elements, Г _THzFor the Terahertz electric field loads the phase delay that the zinc telluridse crystal 6 causes.

(3) the absolute electric field intensity of calculating Terahertz: 1., 2. obtain the Terahertz electric field according to formula and load the phase delay that the zinc telluridse crystal 6 causes:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\arcsin (\frac{I_T^{\mathrm{THz}\&NotEqual;0}}{I_T^{\mathrm{THz}=0}}-1)$ ③

Owing to for the zinc telluridse crystal 6 in the scheme shown in Figure 1, have relational expression:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}{\mathrm{Ln}}^3{r}_{41}{E}_{\mathrm{THz}}$ ④

3., 4. combinatorial formula and can obtain the outer absolute electric field intensity of tested THz wave of plane of crystal in conjunction with zinc telluridse electro-optic detection crystal to the reflection case of terahertz pulse and be:

$E_{\mathrm{THz}}=\frac{{\mathrm{\&Gamma;}}_{\mathrm{THz}}{\mathrm{\&lambda;}}_0}{2\mathrm{\&pi;}{\mathrm{Ln}}^3{r}_{41}}\&CenterDot;\frac{1}{1-{\mathrm{<figure-callout\; id="5"\; label="R\; THz"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{THz}}}$ ⑤

In the formula, λ ₀Be the centre wavelength of laser, λ ₀=800nm; L is the thickness of zinc telluridse crystal 6, L=200 μ m; N is the refractive index of zinc telluridse crystal 6 to exploring laser light, n=2.85; r ₄₁Be the electrooptical coefficient of this zinc telluridse crystal 6, r ₄₁=4.0 * 10 ¹²M/V; Because the zinc telluridse crystal is to the refractive index n of THz wave _THz≈ 3, thereby R is arranged _THz=0.5.

(4) gather the terahertz pulse hot spot, obtain terahertz pulse spot size size:

A, adopt single chirped pulse electro-optic detection scheme as shown in Figure 2, by paraboloidal mirror THz wave is converged on the zinc telluridse crystal 6, the detecting light beam of measuring the conllinear backpropagation by the mode of pump probe obtains the terahertz pulse spot size then.For obtaining the ratio of best signal background, quarter-wave plate 9 has been rotated 2 to 3 degree (near linear polarization).With convex lens 7 crystal is imaged on charge-coupled image sensor 14 (CCD) array.Imaging is that 200 microns fine wire is calibrated with a diameter, and its transformation factor that provides is 5.0 μ m/pixel.The hot spot of THz wave deducts by imaging when terahertz signal is arranged that imaging obtains when not having terahertz signal.

B, with the terahertz pulse hot spot that obtains, obtain spot size (e through over-fitting ^-2Radius doubly) be: the x direction is 1.22 ± 0.04mm; The y direction is 1.19 ± 0.08mm, and this correspondence the halfwidth (fwhm) of 1.4 ± 0.06mm.

(5) by on the Terahertz hot spot area A and the energy that can obtain terahertz pulse of the integration on the terahertz pulse duration t be:

$U_{\mathrm{THz}}={\mathrm{\&epsiv;}}_{0}c\&CenterDot;2\mathrm{\&pi;}\frac{{\left(\mathrm{fwhm}\right)}^2}{8\ln 2}\&CenterDot;\underset{t}{\&Integral;}{E}_{\mathrm{THz}}^2\left(0\right)\mathrm{dt}=(2.6\&PlusMinus;0.2)\&times;{10}^{-9}\mathrm{<figure-callout\; id="6"\; label="J"\; filenames="H2009101360094E0000011.png"\; state="\{\{state\}\}">J</figure-callout>}$ ⑥

The error of the value of a half width that the error among the result is mainly introduced when calculating spot size.

Obviously, those skilled in the art can carry out various changes and distortion to the present invention and not break away from the spirit and scope of the present invention.If these modifications and distortion belong within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and is out of shape interior.

Claims (2)

1. the method for measuring pumping electrooptics of a Terahertz impulse energy is characterized in that: may further comprise the steps:

(1) obtains exploring laser light spectrum: adopt single chirped pulse electro-optic detection method, regulate that angle becomes 45 degree between quarter-wave plate crystallographic axis and laser polarization direction, had respectively and the exploring laser light spectrum when not loading terahertz pulse;

(2) analyze the intensity in transmission of exploring laser light: according to obtain in the step (1) do not load terahertz pulse the time exploring laser light spectrum, analyze and survey optical transmission intensity when not loaded terahertz pulse:

$I_T^{\mathrm{THz}=0}=\frac{1}{2}{I}_0\&CenterDot;T$ ①

Exploring laser light spectrum during according to the loading terahertz pulse that obtains in the step (1), analyze and survey optical transmission intensity when obtaining being loaded with terahertz pulse:

$I_T^{\mathrm{THz}\&NotEqual;0}=\frac{1}{2}(1+\sin {\mathrm{\&Gamma;}}_{\mathrm{THz}})I_0\&CenterDot;T$ ②

I in the formula ₀Be the light intensity of incident detecting light beam, T is the transfer coefficient of crystal and other optical elements, Г _THzFor loading the phase delay that terahertz pulse causes;

(3) the absolute electric field intensity of calculating terahertz pulse: 1., 2. obtain loading the phase delay that terahertz pulse causes according to formula:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\arcsin (\frac{I_T^{\mathrm{THz}\&NotEqual;0}}{I_T^{\mathrm{THz}=0}}-1)$ ③

Owing to for the zinc telluridse electro-optic crystal that is adopted in step (1) the electro-optic detection technology, have relational expression:

${\mathrm{\&Gamma;}}_{\mathrm{THz}}=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}{\mathrm{Ln}}^3{r}_{41}{E}_{\mathrm{THz}}$ ④

3., 4. combinatorial formula and is proofreaied and correct the reflection of terahertz pulse in conjunction with zinc telluridse electro-optic detection crystal and can be obtained the outer absolute electric field intensity of tested THz wave of plane of crystal and be:

$E_{\mathrm{THz}}=\frac{{\mathrm{\&Gamma;}}_{\mathrm{THz}}{\mathrm{\&lambda;}}_0}{2\mathrm{\&pi;}{\mathrm{Ln}}^3{r}_{41}}\&CenterDot;\frac{1}{1-R_{\mathrm{THz}}}$ ⑤

In the formula, λ ₀Centre wavelength for laser; L is the thickness of crystal; N is the refractive index of crystal to exploring laser light; r ₄₁Be the electrooptical coefficient of crystal, Be the reflectance coefficient of Terahertz electric field at the electro-optic detection plane of crystal, wherein n _THzBe the refractive index of crystal to THz wave;

(4) gather the terahertz pulse hot spot, obtain terahertz pulse spot size size: the terahertz pulse hot spot is by off axis paraboloidal mirror THz wave to be converged on the zinc telluridse crystal, utilizes charge coupled array that the detection photoimaging is obtained by pumping detecting method and delustring technology then; Afterwards, by being carried out match on horizontal and vertical lines shape, the terahertz pulse hot spot obtains spot size;

(5) calculate the energy of terahertz pulse according to following formula:

$U_{\mathrm{THz}}={\mathrm{\&epsiv;}}_{0}c\underset{A,t}{\&Integral;\&Integral;}{E}_{\mathrm{THz}}^2\mathrm{dAdt}$ ⑥

In the formula, A is the terahertz pulse facula area, and t is the terahertz pulse duration, ε ₀Be permittivity of vacuum, c is the light velocity in the vacuum.

2. according to the method for measuring pumping electrooptics of the described a kind of Terahertz impulse energy of claim 1, it is characterized in that: obtain the terahertz pulse hot spot in the step (4) and adopted single chirped pulse electro-optic detection method and delustring technology.

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