CN104614082A - TeraHertz wave line width measurement device and method - Google Patents

Abstract

The invention belongs to the technical field of TeraHertz wave detection and discloses a scanning fabry-perot interferometer used for line width measurement at a TeraHertz wave band. According to the technical scheme, TeraHertz wave line width measurement device and method include that incidence TeraHertz wave is emitted to a fabry-perot interferometer endoscope in parallel after passing a first off-axis parabolic mirror plated with gold at the surface; a fabry-perot interferometer endoscope a and a fabry-perot interferometer endoscope b are fixed at positions made of high-resistance silicon material; a stepping mobile platform performs stepping movement along the TeraHertz wave propagation direction; the parallel incidence TeraHertz wave from the endoscope b is gathered through a second off-axis parabolic mirror plated with gold at the surface; the focal position of the second off-axis parabolic mirror plated with gold at the surface is provided with a chopper, the second off-axis parabolic mirror plated with gold at the surface outputs the TeraHertz wave, and the measurement result is output through the chopper, a pyroelectric detector and an AD converter. The TeraHertz wave line width measurement device and method are mainly used for the TeraHertz wave detection.

Description

The device and method of THz wave wire width measuring

Technical field

The invention belongs to THz wave detection technique field; Specifically, the device and method of THz wave wire width measuring is related to.

Technical background

Terahertz emission source much dissimilar is in recent years obtained for very large development, and is widely used in the field such as imaging, spectral analysis.At tera-hertz spectra analysis field, terahertz time-domain spectroscopic technology, owing to usually can only realize the spectrally resolved ability of tens of GHz, can not meet actual demand in certain applications.In this context, there has been proposed and utilize the narrow-linewidth single frequency THz source of frequency-tunable to carry out spectral detection.Emerge at present the single-frequency terahertz emission source of some narrow linewidths, such as, based on the terahertz emission source etc. of nonlinear difference or parametric oscillation technology.The output linewidth of narrow linewidth THz source can reach hundred MHz, close to the Fourier transform limit.Utilize this THz source to set up terahertz light spectral analysis system, the precision of spectral detection can reach MHz magnitude.Along with the development in terahertz emission source, the performance in terahertz emission source constantly promotes, and the measurement realizing comprising it every critical performance parameters of output linewidth has shown the importance constantly highlighted.In order to realize the Measurement accuracy of THz source radiation live width, search out the target that a kind of measuring accuracy THz wave line width measuring method high, easy to use becomes people's pursuit.

At traditional laser field, the live width using Fabry-Perot etalon to measure laser is current the most widely used a kind of technology.Observed the fine structure of the interference circle of laser after etalon by area array cameras, the live width size of testing laser can be obtained rapidly and accurately.In Terahertz field, the cost of area array cameras is far away higher than the cost of area array cameras in laser field, and thus this measuring method is not suitable for and directly promotes in Terahertz field.As a kind of improved form of Traditional Method F-P etalon, the long variable scanning Fabry-Perot interferometer of interference cavity can the fixing Fabry-Perot etalon of alternate thicknesses, realizes the observation of fine structure of spectral line under the prerequisite not using area array cameras.The scanning Fabry-Perot interferometer improved needs two extra equipment to realize the observation of interference fine structure, is respectively a high-precision displacement platform and a Terahertz power detection device.Along with the development of Terahertz Technology, THz wave power detection device has emerged a lot of different types of product, and the technology realizing THz wave power detected with high accuracy is at ambient temperature quite ripe.In addition, because Terahertz wavelength is longer, close to millimeter magnitude, the requirement of scanning Fabry-Perot interferometer to the mobile accuracy of displacement platform for terahertz wave band is corresponding lower.Therefore, the scanning Fabry-Perot interferometer realizing being applied to wire width measuring at terahertz wave band has possessed the condition of comparative maturity.

Summary of the invention

For overcoming the deficiencies in the prior art, the scanning Fabry-Perot interferometer being applied to wire width measuring is realized at terahertz wave band, for this reason, the technical scheme that the present invention takes is, the method of THz wave wire width measuring, utilize Fabry-Perot FP interferometer, record power transmitance to wavelength X, by formula:

$T\left(d\right)={[1+\frac{{4R}^2}{{(1-R)}^2}{\sin }^2(2\mathrm{\π}\mathrm{nd}\cos \mathrm{\θ}/\mathrm{\λ})]}^{-1}.$

Obtain the long d of interference cavity, in formula, R is the reflectivity of two reflectings surface, and n is the refractive index of filled media between reflecting surface, and θ is incident angle;

Expression formula according to the Free Spectral Range FSR of Fabry-Perot interferometer:

FSR＝c/2nd

Obtain FSR;

Again by formula:

Linewidth(FWHM)＝FSR/Finesse

Obtain the live width Linewidth (FWHM) of THz wave, in formula striped fineness Finesse be similar to be one not with the constant of interfering change of cavity length.

Fabry-Perot FP interferometer is utilized specifically to comprise the steps:

Utilize that incident THz wave reflects by surface gold-plating off axis paraboloidal mirror, exiting parallel is to Fabry-Perot interferometer chamber mirror;

High Resistivity Si material is adopted to be used as the fixing Fabry-Perot interferometer chamber mirror a in position, chamber mirror a two surface finish, mirror a two polished surfaces in chamber have the angle of wedge of about 1 degree to avoid inner formation FP resonator cavity, and the surface near Fabry-Perot interferometer chamber mirror b is vertical with incident THz wave;

Fabry-Perot interferometer chamber mirror b material and physical dimension identical with chamber mirror a, vertical with incident THz wave near the surface of chamber mirror a, chamber mirror b is installed on mobile platform 4;

Along THz wave direction of propagation stepping mobile platform;

Surface gold-plating off axis paraboloidal mirror is utilized the THz wave of the parallel incidence from Fabry-Perot interferometer chamber mirror to be assembled;

Chopper is placed in the focal position of surface gold-plating off axis paraboloidal mirror, the modulating frequency revising THz wave to be measured is the frequency of applicable rear end pyroelectric detector;

Pyroelectric detector, measures the power of transmission THz wave, and the voltage signal that output is directly proportional to probe power size is to data collecting card;

The simulating signal that pyroelectric detector exports is carried out AD conversion, and output digit signals is to computing machine;

Utilize computer run process of measurement, read the digital voltage value that data acquisition system (DAS) exports, work order is sent to step-wise displacement platform; For user calculates wire width measuring result.

The device of THz wave wire width measuring, comprises following structure:

Incident THz wave after the 1st surface gold-plating off axis paraboloidal mirror exiting parallel to Fabry-Perot interferometer chamber mirror;

Fabry-Perot interferometer chamber mirror a is fixed in the position of being made up of High Resistivity Si material, two surface finish, and two surface have the angle of wedge of about 1 degree, and the surface near chamber mirror b is vertical with incident THz wave;

Fabry-Perot interferometer chamber mirror b material and physical dimension identical with chamber mirror a, vertical with incident THz wave near the surface of chamber mirror a, chamber mirror b is installed on mobile platform 4;

Stepping mobile platform is along THz wave direction of propagation step motion;

THz wave from the parallel incidence of chamber mirror b is assembled through the 2nd surface gold-plating off axis paraboloidal mirror;

The focal position of the 2nd surface gold-plating off axis paraboloidal mirror is provided with chopper, and the 2nd surface gold-plating off axis paraboloidal mirror exports THz wave exports measurement result through chopper, pyroelectric detector, AD converter.

Compared with the prior art, technical characterstic of the present invention and effect:

The present invention proposes a kind of low cost, miniaturization, portable Terahertz wire width measuring meter, and there is measuring speed and higher measuring accuracy and reliability faster, can be widely used in being engaged in the laboratory of Terahertz association area.Terahertz wire width measuring meter based on Fabry-Perot interferometer has following advantage: 1. structure is simple, small volume, can use as miniaturization, portable instrument.2. manufacturing cost is lower.3. easy to operate, measure fast.4. measuring accuracy is higher.

Accompanying drawing explanation

Fig. 1 wire width measuring principle schematic.

Fig. 2 patent structure schematic diagram of the present invention.

In figure: 1. surface gold-plating off axis paraboloidal mirror; 2. Fabry-Perot interferometer chamber mirror a (position is fixed); 3. Fabry-Perot interferometer chamber mirror b (index glass) 4. stepping mobile platform; 5. surface gold-plating off axis paraboloidal mirror; 6 choppers; 7. pyroelectric detector; 8. data collecting card; 9. computing machine.

Fig. 3 wire width measuring working-flow sketch.

Fig. 4 two surfaces have the angle of wedge chamber mirror intention of about 1 degree.

Embodiment

Propose a kind of implementation of the Terahertz wire width measuring device based on scanning Fabry-Perot interferometer, this device has compact conformation, cost is lower and can work at ambient temperature, is applicable to the practical application area of Terahertz scientific research field and Terahertz Technology.

The object of the present invention is to provide a kind of scheme of monochromatic THz wave wire width measuring:

According to the Airy formula of multiple-beam interference, do not considering that under the condition absorbed, the saturating power transmitance to wavelength X of Fabry-Perot (FP) interferometer is

$T\left(d\right)={[1+\frac{{4R}^2}{{(1-R)}^2}{\sin }^2(2\mathrm{\π}\mathrm{nd}\cos \mathrm{\θ}/\mathrm{\λ})]}^{-1}.---\left(0.1\right)$

Wherein d is the distance between FP interferometer two reflectings surface, and R is the reflectivity of two reflectings surface, and n is the refractive index of filled media between reflecting surface, and θ is incident angle.When keeping other parameter constant, the transmissivity T of FP interferometer is the function of the long d of interference cavity, the former with the latter change curve as shown in Figure 1.As seen from the figure, curve has periodically, and this characteristic is determined by the sin quadratic term in (0.1) formula.

The present invention introduces striped fineness (Finesse) and Free Spectral Range (Free SpectralRange/FSR) two parameters of Fabry-Perot interferometer.The size of striped fineness is the ratio of the distance of adjacent two interference peaks and the full width at half maximum value (FWHM) of interference curve.The full width at half maximum value (FWHM) of curve as shown in Figure 1.For a specific FP interferometer, striped fineness Finesse can be similar to and think one not with the constant of interfering change of cavity length.The expression formula of the Free Spectral Range FSR of Fabry-Perot interferometer is

FSR＝c/2nd (0.2)

Wherein n is the refractive index of filled media in interference cavity.For the situation in chamber being air, the expression formula of Free Spectral Range can be similar to and be reduced to FSR=c/2d.The unit of Free Spectral Range is hertz (Hz).

The spectral line precision that FP interferometer can be differentiated is determined by its Free Spectral Range, and is determined by the chamber of interferometer is long by the size of the known Free Spectral Range of (0.2) formula.When the chamber length of FP interferometer is changed to 1000mm from 0.1mm, its Free Spectral Range can be reduced to 150MHz from 1.5THz.In the interference curve of Fig. 1, the interval that adjacent two interference peak points are corresponding is when the Free Spectral Range corresponding to ante-chamber length.And interference curve is at the FWHM of this position, be the live width of THz wave.The expression formula of wire width measuring result is,

Linewidth(FWHM)＝FSR/Finesse (0.3)

The present invention is further described below in conjunction with the drawings and specific embodiments.

The specific implementation of Terahertz wire width measuring device as shown in Figure 2.Title and the function of system components are expressed as follows:

1. surface gold-plating off axis paraboloidal mirror.Reflecting surface has the reflectivity close to 100% at terahertz wave band, and the reflecting surface of off axis paraboloid mirror type plays the effect of beam shaping, and incident THz wave is exiting parallel after paraboloidal mirror 1.

2. Fabry-Perot interferometer chamber mirror a (position is fixed).High Resistivity Si material, two surface finish, two surfaces have the angle of wedge of about 1 degree to avoid inner formation FP resonator cavity.The angle of wedge as shown in Figure 4.Without special requirement, as long as two of inboard surfaces are parallel just passable, outside two surperficial towards can be any.Surface near chamber mirror b is vertical with incident THz wave.

3. Fabry-Perot interferometer chamber mirror b (index glass).Material and physical dimension identical with chamber mirror a, vertical with incident THz wave near the surface of chamber mirror a.Chamber mirror b is installed on mobile platform 4.

4. stepping mobile platform.Along THz wave direction of propagation step motion, by computing machine 9 programmed control.

5. surface gold-plating off axis paraboloidal mirror.Identical with paraboloidal mirror 1, for the THz wave of parallel incidence is assembled.

6. chopper.Be placed in the focal position of paraboloidal mirror 5, the modulating frequency revising THz wave to be measured is the frequency of applicable rear end pyroelectric detector 7.

7. pyroelectric detector.Measure the power of transmission THz wave, the voltage signal that output is directly proportional to probe power size is to data collecting card 8.

8. data acquisition system (DAS).The simulating signal that pyroelectric detector exports is carried out AD conversion, and output digit signals is to computing machine 9.

9. computing machine.Operating measurement program, reads the digital voltage value that data acquisition system (DAS) exports, sends work order to step-wise displacement platform.For user calculates wire width measuring result.

The workflow diagram of wire width measuring system as shown in Figure 3.Whole system is controlled by computer program, first carries out initialization and is set by the user scanning step and number of samples.System sets according to hits subsequently, measures the raw data obtaining chamber length and intensity in transmission.The last live width size calculating THz wave to be measured according to live width result expression (0.3).

Claims (3)

1. a method for THz wave wire width measuring, is characterized in that, utilizes Fabry-Perot FP interferometer, records power transmitance to wavelength X, by formula:

$T\left(d\right)={[1+\frac{{4R}^2}{{(1-R)}^2}{\sin }^2(2\mathrm{\π}\mathrm{nd}\cos \mathrm{\θ}/\mathrm{\λ})]}^{-1}.$

Obtain the long d of interference cavity, in formula, R is the reflectivity of two reflectings surface, and n is the refractive index of filled media between reflecting surface, and θ is incident angle;

Expression formula according to the Free Spectral Range FSR of Fabry-Perot interferometer:

FSR＝c/2nd

Obtain FSR;

Again by formula:

Linewidth(FWHM)＝FSR/Finesse

Obtain the live width Linewidth (FWHM) of THz wave, in formula striped fineness Finesse be similar to be one not with the constant of interfering change of cavity length.

2. the method for THz wave wire width measuring as claimed in claim 1, is characterized in that, utilize Fabry-Perot FP interferometer specifically to comprise the steps:

Utilize that incident THz wave reflects by surface gold-plating off axis paraboloidal mirror, exiting parallel is to Fabry-Perot interferometer chamber mirror;

High Resistivity Si material is adopted to be used as the fixing Fabry-Perot interferometer chamber mirror a in position, chamber mirror a two surface finish, mirror a two surfaces in chamber have the angle of wedge of about 1 degree to avoid inner formation FP resonator cavity, and the surface near Fabry-Perot interferometer chamber mirror b is vertical with incident THz wave;

Fabry-Perot interferometer chamber mirror b material and physical dimension identical with chamber mirror a, vertical with incident THz wave near the surface of chamber mirror a, chamber mirror b is installed on mobile platform 4;

Along THz wave direction of propagation stepping mobile platform;

Surface gold-plating off axis paraboloidal mirror is utilized the THz wave of the parallel incidence from Fabry-Perot interferometer chamber mirror to be assembled;

Chopper is placed in the focal position of surface gold-plating off axis paraboloidal mirror, the modulating frequency revising THz wave to be measured is the frequency of applicable rear end pyroelectric detector;

Pyroelectric detector, measures the power of transmission THz wave, and the voltage signal that output is directly proportional to probe power size is to data collecting card;

The simulating signal that pyroelectric detector exports is carried out AD conversion, and output digit signals is to computing machine;

Utilize computer run process of measurement, read the digital voltage value that data acquisition system (DAS) exports, work order is sent to step-wise displacement platform; For user calculates wire width measuring result.

3. a device for THz wave wire width measuring, is characterized in that, structure is:

Incident THz wave after the 1st surface gold-plating off axis paraboloidal mirror exiting parallel to Fabry-Perot interferometer chamber mirror;

Fabry-Perot interferometer chamber mirror a is fixed in the position of being made up of High Resistivity Si material, two surface finish, and two polished surfaces have the angle of wedge of about 1 degree, and the surface near chamber mirror b is vertical with incident THz wave;

Fabry-Perot interferometer chamber mirror b material and physical dimension identical with chamber mirror a, vertical with incident THz wave near the surface of chamber mirror a, chamber mirror b is installed on mobile platform 4;

Stepping mobile platform is along THz wave direction of propagation step motion;

THz wave from the parallel incidence of chamber mirror b is assembled through the 2nd surface gold-plating off axis paraboloidal mirror;

The focal position of the 2nd surface gold-plating off axis paraboloidal mirror is provided with chopper, and the 2nd surface gold-plating off axis paraboloidal mirror exports THz wave exports measurement result through chopper, pyroelectric detector, AD converter.