CN208847653U - Real-time polarization sensitive terahertz time-domain ellipsometer - Google Patents
Real-time polarization sensitive terahertz time-domain ellipsometer Download PDFInfo
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- CN208847653U CN208847653U CN201821465541.1U CN201821465541U CN208847653U CN 208847653 U CN208847653 U CN 208847653U CN 201821465541 U CN201821465541 U CN 201821465541U CN 208847653 U CN208847653 U CN 208847653U
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Abstract
The utility model discloses a real-time polarization sensitive terahertz time domain ellipsometer, its device includes femto second laser instrument, optics beam splitting piece BS, array photoconductive antenna, off-axis parabolic mirror, terahertz polarizer, reflection module, electro-optic crystal, mechanical delay line, optics polarizer, quarter wave plate, detection device, and wherein detection device comprises optics beam splitting piece NPB, half wave plate, Wollaston prism, detection end. The real-time polarization-sensitive terahertz time-domain ellipsometer combines the terahertz time-domain ellipsometer with real-time polarization-sensitive detection, and the P-polarization component and the S-polarization component of a terahertz pulse electric field can be simultaneously obtained by single measurement. The real-time polarization sensitive terahertz time-domain ellipsometer is used for measuring the optical constants of the sample, so that the experimental efficiency and the data precision are improved.
Description
Technical field
The utility model relates to Terahertz Technology fields, ellipse more particularly to a kind of terahertz time-domain of real-time polarization sensitivity
Inclined instrument.Industrial quick obtaining be can be applied in the thickness of optics and infrared band opaque medium.
Background technique
Terahertz (THz) is electromagnetic wave of the frequency in 0.1THz-10THz.The vibration of atom and molecule and rotation energy in substance
Grade generally all falls in this wave band, thus to material characterization and mechanism study in have very important status.However, this
The limitation of one waveband radiation source and detector keeps the exploitation of its spectral instrument equipment still immature.Terahertz based on femtosecond laser
Hereby time-domain spectroscopic technology can simultaneously measuring amplitude item and phase term, without Kramers-Kronig relationship or physics
Model is obtained with the optical constant of substance.In the substance of terahertz wave band " optics thickness (Optically dense) ", generally
Using terahertz time-domain reflection spectrometry.But inevitable phase error leads to not directly lead in this spectral technique
The method for crossing experiment obtains the optical constant of substance.
Terahertz time-domain oval thickness spectrometry is that one kind is expected to solve the technology of the measurement of " optics is thick " sample.As a kind of phase
Dry detection means, the time domain impulse for only needing to obtain S-polarization and P polarization can be completed to measure.Currently, DATA REASONING
The accuracy (accuracy) of precision (precision) and system limits the development of terahertz time-domain ellipsometer.The accuracy of system
The problem of be due to existing terahertz wave band optical component quality not enough and optical system beam Propagation direction it is incomplete
Caused by the reasons such as calibration.Solve the problems, such as this, laboratory technician needs system calibration and Optical System Design early period from the later period
These two aspects is set about.The precision problem of DATA REASONING is since the polarization of the detector of traditional terahertz time-domain spectroscopy system selects
Caused by property.Obtain S-polarization and P polarization information, the rotation Terahertz polarizer that general very important person is.Therefore, one is determined
Print optical constant just needs to measure S-polarization and P-polarization component respectively.Conventional efficient is not only reduced in this way, and can be introduced
The unstability of spectroscopy equipment itself.
Utility model content
Based on this, the purpose of this utility model is the realization single measurement Terahertz electric field in terahertz time-domain ellipsometer
P polarization and S-polarization component determine the optical constant of sample, improve the precision of conventional efficient and data.
The purpose of this utility model is achieved through the following technical solutions:
A kind of terahertz time-domain ellipsometer of real-time polarization sensitivity, including femto-second laser, optical beam splitting piece, array photoelectric
Lead antenna, off axis paraboloidal mirror, the Terahertz polarizer, reflecting module, electro-optic crystal, mechanical delay line, optical polariser, four points
One of wave plate and detection device；
The femto-second laser is for providing femtosecond laser；
Optical beam splitting piece BS is arranged in femtosecond laser optical path, and femtosecond laser is divided into detection light and pump light；
The detection light enters mechanical delay line, after optical polariser and quarter-wave plate, is modulated to justify
Polarization state is incident on electro-optic crystal；
The pump light gives off terahertz pulse after array photoelectric lead antenna；
The terahertz pulse successively pass through off axis paraboloidal mirror PM1, Terahertz polarizer WG, off axis paraboloidal mirror PM2,
After reflecting module, off axis paraboloidal mirror PM3 and off axis paraboloidal mirror PM4, it is accumulated on electro-optic crystal and the detection light weight
Enter detection device after conjunction；
The detection device is visited by optical beam splitting piece NPB, two half wave plates, two Wollaston prisms, balance
Survey device DS and balanced detector DP composition；
After the optical beam splitting piece NPB is set to electro-optic crystal, pulse is divided into two bundles, the first beam pulse is through half
DS detector is inputted after wave plate, Wollaston prism；Second beam pulse inputs DP after half wave plate, Wollaston prism
Detector.
Preferably, the optical beam splitting piece that the optical beam splitting piece BS is 1: 9.
Preferably, the square wave bias voltage for being 22kHz added with modulating frequency on the photoconductive antenna.
Preferably, the off axis paraboloidal mirror PM1 focal length is 3 inches；Off axis paraboloidal mirror PM2 focal length is 8 inches；Off axis
Paraboloidal mirror PM3 focal length is 8 inches；Off axis paraboloidal mirror PM4 focal length is 2 inches.
Preferably, Terahertz polarizer WG1 and terahertz are set between off axis paraboloidal mirror PM3 and off axis paraboloidal mirror PM4
Hereby polarizer WG2.
Preferably, the reflecting module includes two metal wedges and a specimen holder.
Preferably, the electro-optic crystal is the ZnTe of (110) crystal orientation.
Preferably, the optical beam splitting piece for the no polarization selectivity that the optical beam splitting piece NPB is 5: 5.
Preferably, DS detector only responds S-polarization, and DP detector only responds P polarization.
The terahertz time-domain ellipsometer of the real-time polarization sensitivity of the utility model is by terahertz time-domain ellipsometer and in real time
Polarization-Sensitive detection combines, and single measurement can obtain the P polarization and S-polarization component of terahertz pulse electric field simultaneously,
It can be obtained accurately by the calibration to real-time polarization sensing detector using the ratio between the interflection of P polarization and S-polarization spectrum
Ellipsometric parameter to obtain the optical constant of terahertz wave band " optics is thick " material, while effectively having suppressed thrashing,
Improve the precision of conventional efficient and data.
Detailed description of the invention
Fig. 1 is the index path of the terahertz time-domain ellipsometer of real-time polarization sensitivity；
Fig. 2 is Polarization-Sensitive end of probe calibration data；
Fig. 3 is the terahertz time-domain waveform figure reflected from sample silicon face；
The terahertz time-domain waveform figure that Fig. 4 is reflected from metallic aluminum surface；
The ellipsometric parameter of Fig. 5 sample silicon；
The ellipsometric parameter tan ψ of Fig. 6 sample silicon and the relative error (relative variance) of P polarization reflection amplitudes；
The refractive index of Fig. 7 sample silicon；
The extinction coefficient of Fig. 8 sample silicon.
Specific embodiment
Below with reference to embodiment, specific embodiment of the present utility model is described in further detail.Following embodiment
For illustrating the utility model, but it is not intended to limit the scope of the present invention.
The theoretical method of terahertz pulse real-time polarization measurement is as follows:
The free space electro optic sampling (free-space EOS) generally used is configured that 1/2 wave plate, electro-optic crystal, 1/4
Wave plate, the detection light of P polarization pass sequentially through these optical elements, and by terahertz pulse Electric Field Modulated, wherein quarter wave plate with
Optics plane of incidence angle is 45 ° (construction elliptically polarized light with equal amplitude).Here the electro-optic crystal that we use is (110) ZnTe, brilliant
[001] direction of body is in the optics plane of incidence.The then expression formula of the light intensity difference of the P polarization and S-polarization of last outgoing detection light are as follows:
Wherein L is the length of electro-optic crystal, and ω is the angular frequency for detecting light, and c is vacuum light speed, and n is that electro-optic crystal is being visited
Survey the refractive index of optical band, γ41For the non-zero Effect member of electro-optic crystal, StotAlways to detect light intensity, γ is 1/2 wave plate
The angle of fast axle or slow axis and the optics plane of incidence, α are the angle of terahertz pulse electric field and the optics plane of incidence, ETHzFor Terahertz
Time domain impulse electric field, ExAnd EyFor ETHzX and y-component.In this configuration, it can be surveyed by rotating the angle of 1/2 wave plate
Measure different terahertz polarization components.
Polarization resolved measurement in real time in order to obtain, we are by the reversed order of these three optical elements: quarter wave plate, electricity
Luminescent crystal, 1/2 wave plate.Since the Jones matrix of these three optical elements is symmetrical matrix, outgoing detection light P polarization and
The expression formula of the light intensity difference of S-polarization is constant.Therefore, it after electro-optic crystal, will be adjusted with the beam splitting chip of one piece of no polarization selectivity
The detection light 5: 5 of system is divided into two bundles (detection light beam A and detection light beam B).Being respectively put into angle γ in detection light beam A and B is
0 ° and 22.5 ° of 1/2 wave plate.The P polarization of light beam A and the light intensity difference just S with terahertz pulse electric field of S-polarization are detected at this time
Polarized component is directly proportional, detects the P polarization of light beam B and the light intensity difference just P-polarization component with terahertz pulse electric field of S-polarization
Half it is directly proportional.By changing delay line, so that it may while obtaining the terahertz pulse electric field information of P polarization and S-polarization.
1 illustrates that the terahertz time-domain ellipsometer of real-time polarization sensitivity is built in conjunction with the embodiments.
Embodiment 1:
The experimental system built such as Fig. 1.Femto-second laser be commercial ti sapphire laser (Coherent Vitesse,
800nm, 100fs, 80MHz).Wherein, the optical beam splitting piece of BS 1: 9, PCA are array photoelectric lead antenna (Batop
Optoelectronics iPCA 21-05-1000-800-h), PM1 to PM4 is off axis paraboloidal mirror, and focal length is respectively 3 English
Very little, 8 inches, 8 inches, 2 inches, WG, WG1 and WG2 are that (green dotted line frame indicates that the two wiregratings only exist to the Terahertz polarizer
Adjust end of probe response Shi Caihui and be put into optical path), Reflection module is reflecting module (comprising there are two metal wedge MW
It is the electro-optic crystal of (110) crystal orientation with a specimen holder Sample), ZnTe, Time delay is mechanical delay line,
Polarizer is optical polariser (P polarization is polarized), and λ/4 are quarter-wave plate, the light of the no polarization selectivity of NPB 5: 5
Beam splitting chip is learned, λ/2 are half wave plate, and WP is Wollaston prism.DS and DP is the end of probe using balanced detector,
S-polarization and P polarization are only responded respectively.
The femtosecond pulse of laser is pump light and detection light by BS beam splitting.Pump light is incident on array photoelectric lead antenna
On, the square wave bias voltage (high level 10V, low level 0V, the duty ratio that are 22kHz added with modulating frequency on photoconductive antenna
50%), and it rotates by a certain angle so that the P polarization of the terahertz pulse radiated and the amplitude of S-polarization component are approximately equal,
By wiregrating WG after the terahertz pulse of diverging PM1 collection collimation, wiregrating rotates to 45 ° of directions to further such that P is inclined
It shakes equal with the amplitude of S-polarization component.The terahertz pulse for being 45 ° with P polarization angular separation converges such as by PM2
In Reflection module, terahertz pulse is incident on sample surfaces with 60 ° by MW1, the Terahertz reflected from sample surfaces
Pulse is collected by PM3 after the reflection of MW2 and is collimated, and terahertz pulse is converged on crystal detection and and detected by last PM4
Light is overlapped.Detection light enters mechanical time delay line Time delay, after Polarizer and λ/4, quilt after being reflected by BS
It is modulated to circular polarization state, be then incident on crystal detection and is overlapped with Terahertz focus.By changing Time delay, detection
Pulse and terahertz pulse can be overlapped in time, and by electrooptic effect, the polarization state of direct impulse can be by terahertz pulse tune
System.The direct impulse modulated is divided into two bundles by NPB, a branch of input DS detector, the angle of half wave plate in DS detector
Degree is 0 °；Another beam is input to DP detector, and the angle of half wave plate is 22.5 ° in DP detector.In two detectors
In, polarization variations are measured using balance detection method, so as to extract the information of S-polarization and P polarization.
DP and DS detector is made only to respond P polarization and S-polarization Terahertz respectively, it is necessary to accurately adjust λ/4, visit
Survey the angle of crystal, two this four optical elements of λ/2.Two WG1 and WG2 (the two wiregratings are placed between PM3 and PM4
Extinction ratio be about 500), by the angle for rotating the two wiregratings, so that it may two detectors are adjusted.Firstly the need of
Measurement obtains [001] direction of ZnTe (110), and by [001] along P polarization direction (the optics plane of incidence).By λ/4 and two λ/
2 rotate to respective angles.But since the label of the fast axle of wave plate or slow axis is not generally very accurate, it is therefore desirable to use wiregrating
WG1 and WG2 construction S-polarization or P polarization Terahertz, then rotate λ/4 and two λ/2 polarize DS (DP) for P (S)
It responds small as far as possible.After regulating, we allow WG1 only by S-polarization Terahertz, then rotate WG2, examine DS and DP pairs
In the response of Terahertz.If Fig. 2 is corresponding response curve, it was demonstrated that our end of probe has real-time polarization resolving power.
Illustrate the measurement method of optical constant below with reference to embodiment 2.
Embodiment 2:
Sample to be tested is fixed on specimen holder first.Since NPB, electro-optic crystal, detector can not reach ideal
State, it is therefore desirable to be calibrated for DS and DP.The difference of DS and DP polarization response can indicate are as follows:
Wherein,For the Fourier transformation of differential signal measured by DP (DS) detector,For DP (DS)
The polarization response of detector,For the Jones matrix of sample,WithThe P-polarization component of respectively incident Terahertz electric field
And S-polarization component.By adjusting the angle of electro-optic crystal and half wave plate, detector DS and DP can achieve very high disappear
Light ratio, thereforeWithCan be with approximate representationWithFor isotropic sample,Expression formula are as follows:
Wherein Ψ and Δ are the ellipsometric parameters of sample, is defined as:
WhereinFor the ratio between P polarization and the reflection coefficient of S-polarization component.Therefore,WithIt can be expressed as:
Then ellipsometric parameter can be rewritten are as follows:
WithIt can experimentally measure to obtain.ForNumerical value can pass through metallic aluminium mirror
Measurement calibration.It this is because metal is very big in the complex refractivity index of terahertz wave band, such as in wavelength is 250 μm for metallic aluminium
Complex refractivity index be 531+689.7i, therefore its ellipsometric parameter Ψ and Δ extremely level off to Pi/4 and Pi.Can thus it pass through
P polarization and the ratio between the S-polarization of speculum are measured to determineSo that it is determined that the ellipsometric parameter of sample.
Sample negligible for surface roughness, dielectric constant can indicate are as follows:
Wherein,For the relative dielectric constant of sample, complex refractivity indexWith the pass of relative dielectric constant
System isWherein n is refractive index, and κ is extinction coefficient.
Using the system built, the terahertz time-domain waveform from sample silicon and metallic aluminium mirror surface reflection is measured, such as
Shown in Fig. 3 and Fig. 4.By Fourier transformation, its spectrum information can be obtained.(6) are arrived using equation (2), so that it may obtain sample silicon
Ellipsometric parameter, as shown in Figure 5.Fig. 6 is the ellipsometric parameter tan ψ of sample silicon and the relative error (opposite side of reflection amplitudes
Difference), due to the superiority of real-time polarization resolution system, all exist in entirely measurement wave band, the relative error of ellipsometric parameter tan ψ
1% or less.Fig. 7 and Fig. 8 is to utilize ellipsometric parameterThe complex refractivity index (soft dot) being calculated with equation (7).On therein
Lower triangle is carried out wherein Drude model is utilized to phase term by traditional terahertz time-domain reflective spectral measure
Amendment.The result of two systems meets well.
It, cannot the above content is specific preferred embodiment further detailed description of the utility model is combined
Think that the specific implementation of the utility model is limited only to these explanations.For the ordinary skill of the utility model technical field
For personnel, under the premise of not departing from the utility model design, several simple deduction or replace can also be made, all should be considered as
Belong to the protection scope of the utility model.
Claims (9)
1. a kind of terahertz time-domain ellipsometer of real-time polarization sensitivity, which is characterized in that including femto-second laser, optical beam splitting
Piece, array photoelectric lead antenna, off axis paraboloidal mirror, the Terahertz polarizer, reflecting module, electro-optic crystal, mechanical delay line, optics
The polarizer, quarter-wave plate and detection device；
The femto-second laser is for providing femtosecond laser；
Optical beam splitting piece BS is arranged in femtosecond laser optical path, and femtosecond laser is divided into detection light and pump light；
The detection light enters mechanical delay line, after optical polariser and quarter-wave plate, is modulated to circular polarization
State is incident on electro-optic crystal；
The pump light gives off terahertz pulse after array photoelectric lead antenna；
The terahertz pulse successively passes through off axis paraboloidal mirror PM1, Terahertz polarizer WG, off axis paraboloidal mirror PM2, reflection
After module, off axis paraboloidal mirror PM3 and off axis paraboloidal mirror PM4, be accumulated on electro-optic crystal and the detection light be overlapped after
Into detection device；
The detection device is by optical beam splitting piece NPB, two half wave plates, two Wollaston prisms, balanced detectors
DS and balanced detector DP composition；
After the optical beam splitting piece NPB is set to electro-optic crystal, pulse is divided into two bundles, the first beam pulse is through half wave
DS detector is inputted after piece, Wollaston prism；Second beam pulse inputs DP spy after half wave plate, Wollaston prism
Survey device.
2. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that the optical beam splitting piece
BS is the optical beam splitting piece of 1:9.
3. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that the photoconductive antenna
On added with modulating frequency be 22kHz square wave bias voltage.
4. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that the off axis paraboloid mirror
Mirror PM1 focal length is 3 inches；Off axis paraboloidal mirror PM2 focal length is 8 inches；Off axis paraboloidal mirror PM3 focal length is 8 inches；It is off-axis to throw
Object plane mirror PM4 focal length is 2 inches.
5. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that off axis paraboloidal mirror
Terahertz polarizer WG1 and Terahertz polarizer WG2 is set between PM3 and off axis paraboloidal mirror PM4.
6. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that the reflecting module packet
Include two metal wedges and a specimen holder.
7. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 4 or 5, which is characterized in that the electric light is brilliant
Body is the ZnTe of (110) crystal orientation.
8. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that the optical beam splitting piece
NPB is the optical beam splitting piece of the no polarization selectivity of 5:5.
9. the terahertz time-domain ellipsometer of real-time polarization sensitivity as described in claim 1, which is characterized in that DS detector only responds
S-polarization, DP detector only respond P polarization.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109115690A (en) * | 2018-09-07 | 2019-01-01 | 中国人民解放军国防科技大学 | Real-time polarization sensitive terahertz time-domain ellipsometer and optical constant measuring method |
| CN114739298A (en) * | 2022-03-10 | 2022-07-12 | 华中科技大学 | Linear terahertz ellipsometer calibrated by using visible light and thickness measuring method |
-
2018
- 2018-09-07 CN CN201821465541.1U patent/CN208847653U/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109115690A (en) * | 2018-09-07 | 2019-01-01 | 中国人民解放军国防科技大学 | Real-time polarization sensitive terahertz time-domain ellipsometer and optical constant measuring method |
| CN114739298A (en) * | 2022-03-10 | 2022-07-12 | 华中科技大学 | Linear terahertz ellipsometer calibrated by using visible light and thickness measuring method |
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