CN104198424B - A kind of method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio - Google Patents
A kind of method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio Download PDFInfo
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Abstract
A kind of method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio, during saturating high frequency is cut down, in the absorbing sheet of low frequency and saturating low frequency abatement, the absorbing sheet of high frequency is placed in the light path after infrared light supply, the part luminous energy sending light source has frequency to absorb targetedly, thus reach to equalize the effect of bias light spectral power distribution, afterwards by improve light source luminous energy make the gross energy received on Infrared Detectors with add absorbing sheet before the gross energy that receives identical, now background spectrum energy at original low energy distribution is greatly improved, thus significantly improve the signal to noise ratio of these frequency ranges；The present invention can avoid due to the signal to noise ratio of harmonious poor some frequency ranges brought of FTIR spectrum Energy distribution and the too low problem of detectivity.
Description
Technical field
The invention belongs to Fourier infrared spectrograph spectral measurement field, improve FTIR spectrum particularly to one
The method of signal to noise ratio frequency range signal to noise ratio that instrument is on the low side.
Background technology
In order to solve the problem of environmental pollution of sternness, it is requisite for seeking a kind of strong monitoring means.In recent years
Carry out Fourier infrared spectrograph (FTIR) owing to its measuring speed is fast, detect wave number wide ranges, can measure various ingredients simultaneously
Significant advantage is widely used in the detection field of pollutant in air, water source, is particularly advantageous for accidental pollution event event medium ring
The urgent detection of border safety.Generally the light path schematic diagram of FTIR detected gas is as in figure 2 it is shown, in figure, use He-Ne laser instrument 1
With infrared light supply 2, emitting beam and expose to after beam splitter 3 on index glass 4 and horizontal glass 5, laser is received by laser detector 7, red
Outer light exposes to sample 8, again through the transmitting of paraboloidal mirror 29 after transmission, via detector after paraboloidal mirror 1 reflects
Diaphragm 10 obtains infrared interference signal 11, and finally gives infrared spectroscopy signals 12.The core of FTIR be have employed infrared beam,
Laser beam shares the design of interferometer, and the positional information using laser interference signal to provide completes the equidistant of infrared interference signal
Interval sampling.Through Fourier transformation direct detection the most at last to infrared interference signal resolution be frequency domain spectra signal, and lead to
Cross contrast background spectrum detection be placed on infrared beam the absorption spectrum of determinand on path, thus obtain determinand
Component information.
FTIR directly depends on the signal to noise ratio of detectable signal to the identification of determinand and accuracy of detection.And due in FTIR
It is additive noise that the main contributions of noise carrys out the thermal noise of source detector, and basic only performance to Infrared Detectors own is relevant, because of
Effective interference signal size that the signal to noise ratio of this FTIR is mainly received by detector and the intrinsic noise size of detector determine.
But, limit owing to High sensitivity infrared detector (such as MCT detector) exists saturation voltage, i.e. the detector sound to incident illumination
Answer voltage only ability and incident illumination energy size linear correlation below saturation voltage.Do not satisfy to make Infrared Detectors be operated in
And state, light intensity attenuation sheet the most also to be installed additional to limit incident illumination merit in the light path using MCT detector in each FTIR producer
Rate, the transmitance (containing light intensity attenuation sheet) of general recommendations MCT detector measurement sample is less than 20%.Atmosphere pollution is supervised
Survey etc. has under the occasion of very high permeability, and substantial amounts of luminous energy cannot be used appropriately.
FTIR directly depends on the signal to noise ratio of detectable signal to the identification of determinand and accuracy of detection.And due in FTIR
It is additive noise that the main contributions of noise carrys out the thermal noise of source detector, and basic only performance to Infrared Detectors own is relevant, in detail
See Griffiths, Peter R.and James A.de Haseth, Fourier Transform Infrared
Spectroscopy, Wiley-Interscience publication, John Wiley&Son (1986), the therefore letter of FTIR
The noise size more intrinsic than the effective interference signal size mainly received by detector and detector of making an uproar determines.But, due to
There is saturation voltage and limit in High sensitivity infrared detector (such as MCT detector), i.e. the detector response voltage to incident illumination
There are ability and incident illumination energy size linear correlation below saturation voltage.In order to make Infrared Detectors be operated in unsaturation state,
Light intensity attenuation sheet the most also to be installed additional to limit incident optical power, typically in the light path using MCT detector in each FTIR producer
The transmitance (containing light intensity attenuation sheet) of suggestion MCT detector measurement sample is less than 20%.Atmosphere pollution monitoring etc. is had
Having under the occasion of very high permeability, the infrared luminous energy of the overwhelming majority cannot be used appropriately.Owing to being limited by saturation voltage,
The inequality extent of FTIR bias light spectral power distribution will have a strong impact on the detection spirit at its spectrally different wave number (frequency) places
Sensitivity.And the Energy distribution of FTIR background spectrum is the most unbalanced in reality, Fig. 3 illustrates ideal black-body at 800K, 1000K,
Radiance curve during 1200K, the corresponding altofrequency of the high wave number (wavenumber) of abscissa in figure.FTIR background spectrum is not
But relevant with light-source temperature, also relevant with the transmitance of the responsiveness of used detector and beam splitter, but in the overwhelming majority
In the case of, its local spectral power distribution all shows as the crest shape that high both sides, middle part are low, the most unbalanced.Fig. 4 is for using phase
Same Global (Everglo) source light source, different detectors (MCT, DTGS), beam splitter (XT-KBr, KBr, CaF2) time
The legend of FTIR bias light spectral curve, quoted from King, P.L., Ramsey, M.S., McMillan, P.F.and Swayze, G.,
Laboratory fourier transform infrared spectroscopy methods for geologic
Samples, in Infrared Spectroscopy in Geochemistry, Exploration, and Remote
Sensing, Mineral.Assoc.of Canada, London, ON, 33,57-91,2004. wherein 3600cm–1With 1600cm–1
The absworption peak of wave number causes due to steam.
The unbalanced meeting of FTIR bias light spectral power distribution causes it in the sensitivity of part detection frequency range and signal to noise ratio very
Low.As a example by energy distribution curve in Fig. 4, the background Energy distribution of FTIR is at intermediate bands distribution height, available higher letter
Make an uproar ratio, and low in the distribution of two ends frequency range, it is thus achieved that signal to noise ratio relatively low, therefore for characteristic spectral line in the detection spirit of the gas at two ends
Sensitivity is the most relatively low.Such as Fig. 5 shows 16 kinds of representative gases absorption spectrum at infrared band, quoted from Louise
C.Speitel.Fourier Transform Infrared Analysis of Combustion Gases, Department
Of transportation Washington DC, 2001；Wherein HCN, the detection sensitivity of HF, C2H2, C2H4 etc. is due to place
Relatively low in low energy distribution region, spectrum two ends, but HCN Yu HF not only has the strongest toxicity, need under less concentration i.e.
Be ascertained, they simultaneously or water-soluble gas, owing to having partial loss in the removal process of gas pretreatment, to them
Minimum detectability require more harsh.
In order to avoid spectrophone Energy distribution too low compared with the accuracy of detection of weakness as far as possible, wide in existing FTIR product
General employing light source launching curve and the method being mutually matched of explorer response curve, choose specific infrared light supply the most as far as possible
Launching curve has the detector of complementary responses curve to reduce the difference of the Energy distribution of its background spectrum, improves low-yield point
Energy at cloth, but the system more mated can selected at present is still difficult to obtain good Energy distribution effect.Some is external
High-grade FTIR also uses the method simultaneously installing the different detector of two or more response curves in a FTIR
Preferable accuracy of detection is all obtained at spectrum different frequency range.Switching between its different detectors is implemented by control system, but light
The cost of spectrometer can be greatly improved.For the universal FTIR of simple detector, the lack of uniformity of background spectrum is still one so far
There is problem to be solved.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, it is an object of the invention to provide a kind of raising FTIR spectrum
The method of signal to noise ratio frequency range signal to noise ratio that instrument is on the low side, to FTIR background Energy distribution spectrally by there being the absorption of frequency selectivity
Abatement reaches to equalize bias light spectrum energy, can be prevented effectively from identification and the accuracy of detection at the more weak place of spectrophone Energy distribution
Too low defect, thus solve in Fourier infrared spectrograph that the distribution of bias light spectrum energy is unbalanced, band segment signal to noise ratio is too low
The problem being unfavorable for detection.
To achieve these goals, the technical solution used in the present invention is:
A kind of method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio, to Fourier infrared spectrograph
A part for the light that the infrared light supply of middle use sends carries out having frequency or wave number optionally to block absorption, cuts down infrared light
The energy of Energy distribution collection Mid Frequency in the spectrum of source, to reduce the inequality extent of whole spectral energy distribution curve；Add simultaneously
Big luminous flux, improves the background spectrum gross energy after absorbing abatement received on detector so that it is reach to disappear
Gross energy when subtracting, finally on the premise of not making Infrared Detectors supersaturation occur, reaches to improve Fourier infrared spectrograph
The effect of the signal to noise ratio of signal to noise ratio frequency range on the low side in background spectrum.
Available have frequency or the selective absorbing sheet of wave number to realize selectivity and block absorption, after absorbing, light
Spectral power distribution WhereinFor spectral frequency or ripple
Number,The light sent for light source spectral power distribution after absorbing equilibrium,Itself is emitted beam for light source
Spectral power distribution,It is respectively the transmitances of two pieces of absorbing sheets having a frequency selectivity, one of is
Thoroughly in high frequency absorption abatement, the absorbing sheet one of low frequency, another block is the absorbing sheet two that low frequency absorbs abatement medium, high frequency, C1、C2、
C3For constant, C1For former light gross energy is not affected by absorbing sheet one and absorbing sheet two to intercept former light shared by the energy of light total
The ratio of energy, C2The ratio of former light gross energy, C is accounted for for being incident on the energy of absorbing sheet one3For being incident on the energy of absorbing sheet two
Amount accounts for the ratio of former light gross energy.
Choose absorbing sheet one and the transmittance curve of absorbing sheet two, obtain according to transmittance curve emulation mode iterative approach
Obtain energy proportion C2、C3Optimal value, to improve as far as possibleBalanced intensity.
Simultaneously need to improve incident luminous flux to luminous flux when not carrying out blocking absorptionTimes, now lead to
Cross the spectrum gross energy after abatement again to bring up to
The present invention also by whether placing absorbing sheet in shift fork slide block switching-over light path, thus can make full use of bottom season spectrum originally
With the mode that the background spectrum after Absorption modulation reaches higher signal to noise ratio.
Compared with prior art, the invention has the beneficial effects as follows:
1, the present invention uses the method that the energy sending infrared light supply has frequency selectivity to absorb, by
Select to the infrared light path between infrared detector inserts the frequency energy to spectral energy is higher after infrared light supply
The absorbing sheet of selecting property abatement, such as after can being inserted in infrared light supply, as shown in Figure 6.Make at high s/n ratio frequency energy significantly
Reduce, reach to improve the effect of Fourier spectrometer bias light spectral power distribution equilibrium degree.
2, it is being difficult to find the frequency of the preferable homogenous material just absorbing the frequency range luminous energy cutting out frequency integrated distribution
Rate selective absorbing abatement sheet in the case of, can select can mainly cut out respectively include Energy distribution collection Mid Frequency and with
The a piece of absorbing sheet of upper frequency and can mainly cut out a piece of absorbing sheet including Energy distribution collection Mid Frequency and frequencies below thereof,
This two panels absorbing sheet is separately inserted in light path, a certain proportion of light must also be retained not by this two panels absorbing sheet, by closing
Reason adjusts the ratio of this three some light, plays the luminous energy proportion reducing original Energy distribution collection Mid Frequency, and improves former
Carry out the ratio shared by the luminous energy of Energy distribution rareness frequency range.
3, by equilibrium Fourier spectrometer bias light spectral power distribution, it is to avoid Fourier spectrometer bias light spectrum energy
Being distributed the most unbalanced, but the spectrum gross energy after absorbing sheet is cut down can than reduce before not adding absorbing sheet, this can pass through
Improve infrared light supply launch power or remove original artificial dispose for avoiding the oversaturated attenuator of detector, do not make red
On the premise of supersaturation occurs in external detector, improve the Energy distribution of original energy frequency range on the low side, thus improve this band segment
Signal to noise ratio and detection sensitivity.
In sum, present configuration is simple, does not change the basic structure of former Fourier infrared spectrograph, in existing Fu
The improvement of leaf infrared spectrometer is the easiest；Only need to use powerful infrared light supply or remove original artificial dispose for avoiding
The oversaturated attenuator of detector, is added with frequency and absorbs abatement sheet targetedly to carry out balancing energy；Can also use
The mode of a kind of switching, utilizes shift fork slide block to switch in the optical path and whether inserts absorption abatement sheet, when not comprising in light path
When absorbing abatement sheet, background spectrum now retains the function that spectrogrph is originally high to Mid Frequency detection sensitivity, and at needs
When detection absorption spectrum is in the gas of former detection sensitivity low frequency range, absorption abatement sheet is switched into light path, thus significantly carries
The signal to noise ratio of the frequency range that plateau detection sensitivity is low.Absorb abatement sheet and Infrared High-Power light source manufacturing cost far below infrared spy
Survey the cost of device, use absorption abatement sheet to equalize background spectrum ratio and use multiple Infrared Detectorss and handover control system thereof to want
The most much.
Accompanying drawing explanation
Fig. 1 is that the infrared light supply of Fourier infrared spectrograph (FTIR) emits beam by absorbing sheet partial interception schematic diagram.
Fig. 2 is traditional Fourier infrared spectrograph (FTIR) light path schematic diagram.
Fig. 3 is ideal black-body radiance curve.
Fig. 4 is different detector (MCT, DTGS), beam splitter (XT-KBr, KBr, CaF2) Fourier infrared spectrograph this
Bottom season is composed.
Fig. 5 is 16 kinds of representative gases absorption spectrums at infrared band.
Fig. 6 is to insert the FTIR light path schematic diagram after spectral energy absorbs abatement sheet after infrared light supply.
Fig. 7 is the spectrophone energy distribution function after former DTGS XT-KBr bias light spectral power distribution and matching
Fig. 8 is the transmittance function of perfect balance process
Fig. 9 is 1mm thickness SiO2Sheet glass covers 0%, 50%, the background spectrum of spectrogrph after 100% total light intensity.
Figure 10 is 1mm thickness SiO2Sheet glass transmittance curve.
Figure 11 is the spectrogram after the equilibrium of C1=0.71.
Figure 12 is the Hg of 10 μ m thick1-xCdxThe Te coating transmittance curve at x=0.1, when 0.15,0.2.
Figure 13 is for through this Hg1-xCdxSpectral distribution curve after Te equalization, wherein x=0.1.
Figure 14 is the energy distribution curve after equilibrium, C1=0.18, C2=0.43, C3=0.39, x=0.1, ρdis=
3.53/6.86=51.5%.
Figure 15 is the result after energy of light source improves 4.25 times.
Figure 16, (1) solid line: bottom season spectrum originally, (2) dotted line: through absorbing the background spectrum of abatement sheet.
Detailed description of the invention
Embodiments of the present invention are described in detail below in conjunction with the accompanying drawings with embodiment.
The present invention is a kind of method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio, at infrared light supply
Carry out selectivity abatement to the infrared light path between infrared detector inserts the frequency energy to spectral energy is higher afterwards
Absorbing sheet, such as after can being inserted in infrared light supply, as shown in figures 1 to 6.Energy at high s/n ratio frequency is made significantly to drop
Low, thus reach to improve the purpose of bias light spectral power distribution equilibrium degree.After spectral power distribution relatively equalizes, can be by carrying
High IR light source launch power or remove original artificial dispose for avoiding the oversaturated attenuator of detector, thus improve originally
Bottom season spectrum gross energy is to close to the gross energy before abatement, on the premise of not making Infrared Detectors supersaturation occur, reaches to improve
The signal to noise ratio of signal to noise ratio frequency range on the low side in Fourier infrared spectrograph background spectrum, takes into account other frequency ranges simultaneously and remains to reach required
The effect of signal to noise ratio.Another application mode of the method be use shift fork to stir absorbing sheet, with switch absorbing sheet insert
Enter or exit light channel.When absorbing sheet is not inserted into light path, spectrogrph can obtain the basis that original intermediate bands energy is higher
Bottom season is composed, and switches to obtain, when absorbing sheet inserts light path, the new background spectrum that both sides band energy is higher.Comprehensive two bases
Bottom season spectrum can obtain more preferable Effect on Detecting.
Detailed process and the method for above two application mode are as follows:
Embodiment 1
1, the transmittance function of the light intensity method of residues determines
The FTIR of different company's different model is due to its light source, detector, the difference of spectroscope performance, and its background spectrum divides
Cloth might not be identical, and the present invention explains as a example by the FTIR background spectrum in Fig. 4 and its background spectrum is carried out equalization
Method, the method is for having mid portion Energy distribution high two end portions energy in the range of the mid-infrared that is similar in Fig. 4
It is distributed low this most common FTIR background spectrum and there is universality.
As shown in Figure 6, basic structure still uses FTIR to detect light path, except that, at the transmitting route of infrared light supply 2
On be provided with absorbing sheet 1 and absorbing sheet 2 14, wherein, in absorbing sheet 1 saturating high frequency absorption abatement, low frequency, absorbing sheet two
14 saturating low frequencies absorb abatement medium, high frequency.As it is shown in figure 1, the light that infrared light supply 2 sends is by absorbing sheet 1 and absorbing sheet 2 14
Carry out selectivity and block absorption.
Owing to this FTIR background spectrum is 500cm in wave number-1Following Energy distribution is too low, and the present invention is to this background spectrum
Equalization also focuses on and makes 4000cm-1To 500cm-1In the range of spectral balanced.500cm-1-400cm-1In the range of energy divide
Although cloth the most also will than be greatly improved before equilibrium, but it could not be expected that to bring up to the Energy distribution close with its elsewhere strong
Degree.For the ease of calculating, the Energy distribution of the DTGS XT-KBr background spectrum in Fig. 4 is carried out numerical fitting, matching has been picked
Except the absworption peak of steam, carbon dioxide etc., the curvilinear function after matching isAs it is shown in fig. 7, whereinFor wave number.
Bias light spectrum energy is positioned at 500cm-1With 4000cm-1The size at place is respectively 8 and 8.5, is positioned at peak 1500cm-1Size
It is 38.Spectral energy size in figure is relative value.
From the point of view of background spectrum, an equalization process, an equalization transmittance function can be equivalent toOriginally
Bottom season spectral distribution function becomes the bias light Spectral structure after equilibrium after being multiplied by transmittance function.
For perfect balance, i.e. 400cm after equilibrium-1To 4000cm-1Energy is identical everywhere.If protecting after equalization
Hold bottom season originally to compose at 4000cm-1The energy at place is constant, i.e. at 4000cm-1PlaceIt is 1, the spectrophone in Fig. 7 is divided
ClothThe transmittance function of preferable equalization process can be obtained after substituting into (2)See Fig. 8.
The strongly frequency selective method of residues of light that the present invention is introduced seeks to construct as far as possible close to this transmittance functionLight intensity abatement process.But in reality, at least there is presently no the absorption abatement sheet that can realize perfect balance, can only
In existing material, as far as possible screen or develop absorbing sheet relatively, ultimately constructed go out transmittance functionCan be with
PreferableThere is difference.
2, the bias light spectral power distribution after there is lower wave number light intensity abatement absorbing sheet is added
The absorption characteristic major part of the optical glass on market is all high wave number (high frequency) light strong through penetration power, absorbs
Lower wave number (low frequency) light that penetration power is weak.In order to improve the bias light spectral balancing degree after modulation as far as possible, lower wave number is absorbed
Material, needs to use transmittance curve high wave number section to be comparatively close in Fig. 8 the high wave number that preferable transmittance curve wishes to promote
Section, and it suddenly drops section and can cut down the material absorbing bottom season spectrum peak wave band originally.
This example selects the thick SiO of a piece of 1mm by test2Sheet glass is placed in the light path at next-door neighbour's infrared light supply, test
Infrared spectrometer (FTRX Monolith 20OEM) background spectrum is by SiO2Sheet glass intercepts the change after absorbing.
In Fig. 9, curve is SiO2Sheet glass has intercepted 0%, 50% respectively, and the spectral power distribution after 100% luminous energy is bent
Line, Figure 10 is 1mm thickness SiO that this experiment is measured2The transmittance curve of sheet glass.Transmittance curve is to be passed fully through by when light source
SiO2Spectral energy distribution curve after sheet glass obtains divided by script bottom season spectral curve.
SiO from Fig. 92Sheet intercepts the curve of 50% luminous energy it can be seen that owing to the light of 50% receives the impact of absorption,
New background spectrum is in wave number 1000cm-1To 3000cm-1Section has preferable harmony relative to uncovered curve.
Applying this transmittance curve to be modulated background spectrum in Fig. 7, the bias light spectral power distribution after modulation is
Wherein C1For SiO2The proportion of gross energy, therefore 1-C shared by the beam energy that sheet glass is intercepted1It is and is not blocked
The proportion of gross energy shared by the beam energy cut.Background spectrum (the 4000cm ideally made after modulation of modulation-1-
500cm-1) equilibrium degree as far as possible good, here it is shown that a C1Spectrogram after the equilibrium of=0.71, wave number 4000cm-1-
1500cm-1Maximum spectrum I in Duanmax=11.1, minimum spectrum Imin=6.53, minimum and maximum spectrum compares ρdis=Imin/Imax=
0.606.This composes than script bottom seasonAt 4000cm-1-1500cm-1ρ in Duandis=8.5/38=0.224 has had and has significantly carried
Due to the existence of Absorption modulation, new background spectrum is in wave number 1000cm-1To 3000cm-1Section is set a song to music relative to former light
Line has preferable harmony.But, although the method makes new bias light Spectral structure compare old spectrum at the energy of high wave number section
Distribution increases, but the lower wave number section < 1000cm that background is spectrally the faintest-1The energy of section declines the most further
?.Therefore, the absorption depending a lower wave number abatement absorbing sheet alone can only improve the high wave number section that bias light spectral power distribution is more weak
Energy relative to gross energy proportion, in order to background spectrum is carried out ideal equalization, in addition it is also necessary to a Gao Bo
Number abatement absorbing sheet improves the energy proportion of the most weak lower wave number section of bias light spectral power distribution.
3, the design of high wave number light intensity abatement absorbing sheet: band gap absorber
Background spectrum (because using different light source, detector and beam splitter) its peak due to the FTIR of different model
Position is not fixed, typically at 1300cm-1-2500cm-1Between, see Fig. 4.The lower wave number abatement absorption said for upper joint can
Regulate and control choosing the optical glass of suitable transmittance curve from optical glass storehouse, and high wave number abatement is absorbed
One end then needs to design on demand the transmittance curve of adjustment, and the present invention uses Hg1-xCdxThe method of Te band gap absorber realizes
This mechanism.
Band (energy) gap refer to the valence band top of quasiconductor or insulator to conduct the energy difference of band bottom away from.There is band gap
Material the absorption of spectrum is concentrated on photon energy higher than the frequency of band gap.
For Hg1-xCdxFor Te material, its CdTe component is metal, and HgTe component is quasiconductor.According to contained
Ratio x of HgTe from CdTe different, Hg1-xCdxThe band gap width of Te arbitrarily can regulate to the scope of about 1.5eV from 0eV.
G.L.Hansen, J.L.Schmit, and T.N.Casselman, at Energy gap versus alloy composition
and temperature in Hg1-xCdxTe, J.Appl.Phys.53 (10) 1982, the empirical equation be given in 7099-7101
As follows:
Eg(t, x)=-0.302+1.93x+ (5.35 10-4)(1-2x)-0.31x2+0.832x3 (4)
Wherein band gap width EgIt it is the function of component ratio x and ambient temperature t simultaneously.Due to photon energyTransformational relation between the energy that wavelength and photon are had is
λp=1.24/Eg (5)
Hg1-xCdxThe cut-off frequency that incident illumination is absorbed at front end by Te can be approximately,
λp=(-0.244+1.556x+ (4.31 10-4)(1-2x)t-0.65x2+0.671x3)-1 (6)
To photon energy it isLight at Hg1-xCdxThe calculating of the transmitance in Te coating at V.Gopal,
R.Ashokan and V.Dhar, Compositional Characterization of HgCdTe Epilayers by
Infrared Transmission, Infrared Phys, Vol.33, No.1, (1992) 39-45 has detailed annotation, according to therein
Hg1-xCdxThe Hg at suprabasil 10 μ m thick of CdTe that Te transmitance computing formula calculates1-xCdxTe coating at x=0.1,
When 0.15,0.2, at a temperature of 300K, the transmittance curve of (even substrate) is as shown in figure 12:
Finally wish the equalization transmittance curve reachedIt is two transmittance curve (1) SiO2Sheet (2) Hg1- xCdxThe linear combination of the Weight of the curve that Te and (3) nothing absorb.Wherein SiO2The transmittance curve of sheet mainly has with high wave number
Close, and Hg1-xCdxThe transmittance curve of Te is the most relevant with lower wave number.Therefore Hg should be made1-xCdxThe transmittance curve of Te as far as possible with
Preferable equalization transmittance curve in Fig. 8Middle lower wave number section is consistent.Hg of the present invention1-xCdxTe's is saturating
The rate curve of mistake is the curve of 10 μ m-thick.Single through this Hg1-xCdx(without SiO after Te equalization2Chip equalization) spectral energy
Distribution curve is as shown in figure 13:
4, the general effect after two kinds of light intensity abatement absorbing sheets is inserted
Use SiO2With Hg1-xCdxThe energy distribution curve of the spectrum after Te Absorption modulation can be write as
Wherein C1, C2, C3It is respectively in elementary beam energy without absorbing, by SiO2Sheet absorbs and by Hg1-xCdxTe sheet absorbs
The proportion of part, C1+C2+C3=1,0 < C1, C2, C3<1.The numerical simulation curve of the result after modulation is as shown in figure 14:
Background spectrum gross energy after input light energy raising 4.25 times is made equalization (ignores ripple when being original gross energy
Number is higher than 4000cm-1The impact of energy) as shown in figure 15.Result shows, the Energy distribution of this background spectrum is than before by equalizing
21.25% bring up to equilibrium after 51.47%.Have HCN absworption peak lower wave number section rise to 63.8%-66.9%,
There iing the high wave number section (3500-4000cm of HF absworption peak-1) rise to 35.9%-132%.
Embodiment 2
By whether shift fork slide block switching-over light path is placed absorbing sheet, thus make full use of bottom season spectrum and Absorption modulation originally
After background spectrum reach the mode of higher signal to noise ratio.
The simulation result of above-mentioned embodiment 1 is as shown in figure 15, although low-frequency range, the Energy distribution of high band have obtained greatly
Width improves, but the energy that this raising is the intermediate bands higher with original Energy distribution drops to cost.For avoiding this energy
Decline, can take after light source, utilize in shift fork slide block switching-over light path whether insert absorbing sheet, when being switched to non-band absorbing sheet
Operating mode time, detection originally bottom season spectrum, to keep the high s/n ratio obtaining intermediate bands；It is switched to the shape with absorbing sheet again
State, produces with absorbing sheet and only has the background spectrum of Energy distribution in low-frequency range and high band, reach low-frequency range and height with this
The high s/n ratio of frequency range.The ultimate principle of embodiment 2 is identical with embodiment 1, but the target that Absorption modulation is pursued is not complete
The equalization of frequency range, but only have high s/n ratio in high band and low-frequency range.For example with 1mm thickness SiO in the present invention2Glass
When the transmittance curve of sheet and the suprabasil 10 μm HgCdTe coatings of CdTe reaches this target, its simulation result such as Figure 16 institute
Showing, background spectrum when wherein solid line is to be switched to through hole, dotted line is the background spectrum after being switched to absorbing sheet.This two spectrum
Curve is equal at the gross energy of full frequency band.After using the method, at lower wave number section (500cm-1-600cm-1) luminous energy density carry
A height of 149%-154%, at high wave number section (3200cm-1-4000cm-1) rise to 41%-98%.
The present invention is not limited to above-mentioned detailed description of the invention, in the ken that those of ordinary skill in the art are possessed
In, it is also possible to make a variety of changes on the premise of without departing from present inventive concept.
Claims (3)
1. the method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio, makes in Fourier infrared spectrograph
The part of light that sends of infrared light supply carry out having frequency or wave number optionally to block absorption, cut down infrared light supply spectrum
The energy of middle Energy distribution collection Mid Frequency, to reduce the inequality extent of whole spectral energy distribution curve；Strengthen luminous flux simultaneously,
Improve the background spectrum gross energy after absorbing abatement received on detector so that it is reach gross energy when cutting down,
Final on the premise of not making Infrared Detectors that supersaturation occurs, reach to improve letter on the low side in Fourier infrared spectrograph background spectrum
Make an uproar the ratio effect of signal to noise ratio of frequency range, it is characterised in that utilize and have frequency or the selective absorbing sheet of wave number to realize selectivity and block suction
Receive, after absorbing, the spectral power distribution of lightIts
InFor spectral frequency or wave number,The light sent for light source spectral power distribution after absorbing equilibrium,For
Light source emits beam spectral power distribution itself, It is respectively the saturating of two pieces of absorbing sheets having frequency selectivity
Cross rate, one of cut down for saturating high frequency absorption in, the absorbing sheet one of low frequency, another block is that low frequency absorbs abatement medium, high frequency
Absorbing sheet two, C1、C2、C3For constant, C1For former light gross energy being not affected by absorbing sheet one and absorbing sheet two intercepts light
The ratio of former light gross energy, C shared by energy2The ratio of former light gross energy, C is accounted for for being incident on the energy of absorbing sheet one3For entering
Penetrate the energy at absorbing sheet two and account for the ratio of former light gross energy.
The method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio the most according to claim 1, its feature
It is, chooses absorbing sheet one and the transmittance curve of absorbing sheet two, obtain according to transmittance curve emulation mode iterative approach
Energy proportion C2、C3Optimal value, to improve as far as possibleBalanced intensity.
The method improving Fourier infrared spectrograph signal to noise ratio on the low side frequency range signal to noise ratio the most according to claim 2, its feature
It is, improves incident luminous flux to luminous flux when not carrying out blocking absorptionTimes, after abatement
Spectrum gross energy brings up to again
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| EP0241135A2 (en) * | 1986-03-07 | 1987-10-14 | Hewlett-Packard Company | Flat band optical relay using apertures and simple lenses |
| CN102353630A (en) * | 2011-06-28 | 2012-02-15 | 重庆大学 | Continuous spectrum light source |
| CN203364972U (en) * | 2013-05-29 | 2013-12-25 | 南京斯贝西尔测试技术有限公司 | Test device capable matching with equal energy spectrum curve |
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| EP0241135A2 (en) * | 1986-03-07 | 1987-10-14 | Hewlett-Packard Company | Flat band optical relay using apertures and simple lenses |
| CN102353630A (en) * | 2011-06-28 | 2012-02-15 | 重庆大学 | Continuous spectrum light source |
| CN203364972U (en) * | 2013-05-29 | 2013-12-25 | 南京斯贝西尔测试技术有限公司 | Test device capable matching with equal energy spectrum curve |
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