JPS63269024A - Interference spectroanalyzer - Google Patents

Abstract

PURPOSE:To simplify a constitution, in the Michelson interferometer of a Fourier transform infrared spectroanalyzer, by constituting a beam splitting means of one light pervious plate having a parallel plane equipped with a semi-permeable membrane to correct the phase difference of beam by operation. CONSTITUTION:The interference beam due to a Michelson interferometer 33 equipped with a parallel plane plate 26 splitting the beam from a beam source 1 into two, a fixed reflecting mirror 4 and a movable reflecting mirror 5 transmits through a specimen 11 to be received by an infrared detector 16 to be subjected to Fourier transform and operational processing by an operation apparatus 32. In this case, the beam reflected by the semi-permeable membrane 27 of the plane plate 26 and the beam transmitted therethrough are again superposed on the membrane 27 and, at this time, the square root of the square sum of the respective Fourier transform cosine and sine conversions corresponding to the phase difference of wavelength dependence is also calculated and the phase difference is substantially corrected by operation. Therefore, it is unnecessary to use a correction plate having deliquescence for correcting phase difference and constitution is simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a dispersive spectrometer that performs spectrum analysis of light, and in particular to the structure of an interferometer of a Fourier transform spectrometer using a Michelson interferometer and its related matters. Regarding the calculation method.

[Conventional technology]

Fourier transform spectroscopy uses a two-beam interferometer such as a Michelson interferometer, and changes the optical path difference between the two light beams to convert the interference pattern as a function of the optical path difference into a function of wave number, that is, wavelength, by Fourier transform. This is a device that determines each wavelength component, or spectrum, of a luminous flux. Fourth
The figure shows a schematic configuration of an optical system of a Fourier transform infrared spectrometer according to the prior art. The light source 1 is an infrared light source such as a nichrome wire, and the infrared light emitted from the light source 1 is reflected by a parabolic mirror 2 and becomes parallel light as shown by the dotted line.The Michelson interferometer is surrounded by the dotted line. 3. The Michelson interferometer 3 has a fixed reflector 4. It is composed of a movable reflecting mirror 5 and a light beam splitting means 9 consisting of a parallel plane plate 6° and a correction plate 8.

The plane-parallel plate 6 is transparent to infrared light, and is provided with a semi-transparent mirror film 7 on one surface thereof, which is usually formed by vacuum deposition or the like and has approximately the same transmittance and reflectance. The correction plate 8 is made of exactly the same material as the parallel plane plate 6 and has the same thickness. In the example shown in FIG. 4, the parallel plane plate 6 has a translucent mirror film 7 inclined at 45 degrees with respect to the optical axis 15 of the incident light. The correction plate 8 is arranged parallel to the parallel plane plate 6. Fixed reflector 4. The movable reflector 5 is.

The light reflected by these moves back and forth in front and back of the light incident on each of them. Fixed reflector 4. The light beams reflected by the movable reflecting mirror 5 are superimposed on the semi-transparent mirror film 7 and interfere with each other. This interference light is reflected by the semi-transparent mirror film 7 and is reflected by the parabolic mirror 1.
0, the light is focused on the sample 1 by the parabolic mirror 10, and the light transmitted through the sample 11 passes through the paraboloids @12 and 13 and is focused on the infrared photodetector 14. Due to the semi-transparent mirror film 7, a reflected image Ml' of the reflecting surface M1 of the fixed reflecting mirror 4 is generated on the optical path of the movable reflecting mirror 5, and the rangefinder . twice becomes the optical path difference X between the two light beams superimposed on the semi-transparent mirror film 7. X is also equal to twice the difference in the geometric distances between the point A where the light is split on the semi-transparent mirror film 7 and where they overlap, and the fixed reflecting mirror 4 and the movable reflecting mirror 5, respectively. This optical path difference
Measured by interference. That is, the laser beam 17 is reflected by the reflecting mirror 18 and is made incident on the Michelson interferometer 3, followed by the same path as the infrared light to cause interference, and the interference light is detected by the detector 19. The output of the detector 19 is
- Since periodic intensity changes are given every time the length corresponding to the wavelength of the Ne laser beam changes, this is converted into a pulse signal 21 by the conversion circuit head, the pulse signal 21 is counted, and the movable reflecting mirror 5 is The amount of movement, that is, the optical path difference X is measured.

In order to interfere with He-Ne laser light, some devices are equipped with a separate interference means instead of using the Michelson interferometer for infrared light as described above.

The light beams that interfere on the semi-transparent mirror film 7 have the same amplitude and have an optical path difference X. Therefore, if the amplitude is al and the angular frequency is , then the waveform of the superimposed light beams is 3□: al(-ω
t+ei(ωt-2πXσ))! It is given by il. Here, σ is a wave number and is given by the number of waves of wavelength λ included per unit length, that is, σ=1/2. Applying the relationship eiθ=cosθ+1sinθ to equation (1), we obtain 32:a 1 [cosωt −)−cos (ωt−
2rxa )-1-i (sinωt + 5in(ω
t-2yrxa)) To find the light intensity 1a21 as
-cos(ωt-2ttxty) )2-4- (s
inωt-1-sin(ωt-2xxa) ) ]
=a12[cos2(ωt-πxσ)*cos xxa
-)-5in2(ωt-πxcr) acos2πxcr
] = 2a12[1+cos2πxσ]
(21. Since al corresponds to the intensity of light with wave number σ.

If the spectrum of the luminous flux is B(σ1, then al = 13(σ
It can be set as 1. This can be expressed as all wavenumbers, that is, σ
Integrating over the whole, the light intensity at the optical path difference X is Ffxl= f2B(crl[1+cos2πxσ]d
σ(31 is obtained. F (f that is not a variable of X from xi
2B<σ1dσ minus change I (Xl= 2 f B(σ1cos2πXσdσ
(The detector output corresponding to 41 is called an interferogram. In equation (4), cos 2rx
a = -) [e "" -) - e-i2yrX'] Su (7) Te, I (xi is I Ixl= , l"'Bf
al e i2πXσda (51
Hail to you. By Fourier transforming I fxl, the spectrum B(σ) can be obtained as B(a+=f'"I[xle-"""dσf61. In other words, the output of the infrared photodetector 14 for the measured optical path difference X The interferogram I (xi obtained from Therefore, (the upper and lower limits of the integral of formula 61 are the maximum optical path difference ±L determined by the above movement range. The larger L is, the more I
Because fxl will be smaller.

There is no big problem even if L is finite. Also, the larger L becomes, the better the wave number resolution bait becomes. The three forces B (σ1 is B (crl= f I (xle-12"'
It is obtained by calculating f71Lj.

The pulse signal 21 obtained from the He-Ne laser beam is.

) (Since it is generated every 0.633 μm, which is the wavelength of the e-Ne laser beam, it is used as a sampling signal of Ilxl for the calculation of the calculation device B at the same time as the measurement of the amount of movement of the movable reflecting mirror 5.

In FIG. 4, a sample 1] is placed on the optical path of the light emitted from the Michelson interferometer 3, and the influence of the sample 11 on the spectrum of the light incident on the Michelson interferometer 3 is measured. On the other hand, there is also a method of installing the sample 11 on the optical path of the incident light to the Michelson interferometer 3 and measuring the spectrum of the incident light affected by the sample 11.

Of the light beams incident on the light beam splitting means 9, the light beams directed toward the fixed reflecting mirror 4 and reflected therefrom pass through the parallel plane plate 6 three times and return to the semi-transparent mirror film 7. On the other hand, the light directed toward the movable reflection #, 5 and reflected from there passes through the parallel plane plate 6 only once. However, the correction plate 8 has the same thickness as the parallel plane plate 6.
Therefore, passing through the correction plate 8 twice is the same as passing through the parallel plane plate 6 three times, and at the beam splitting means 9, the reflected light from the fixed reflecting mirror 5 and the movable reflecting mirror are separated. No optical path difference occurs between the reflected lights from 5. The refraction bases of the parallel plane plate 6 and the correction plate 8 differ depending on the wavelength, and the optical path length of the light passing through them differs depending on the wavelength, but by providing the above-mentioned correction plate, this influence can be eliminated.

[Problem that the invention seeks to solve]

Since the Fourier transform spectrometer is a combination of a simple optical system like a Michelson interferometer and a calculation means, there is a high possibility that it can be constructed into a low-cost, popular type of device. It is easy to reduce the cost of the calculation means. On the other hand, since the optical system uses infrared light, the parallel plane plates and correction plates that constitute the beam splitting means are KBr, KCJ,
Expensive products manufactured by optically polishing single crystal plates of halogenated metals with low infrared water absorptivity, such as NacJ and CsI, are used.

Furthermore, these parts are deliquescent, so unlike ordinary mirrors, after a certain amount of use, their performance deteriorates and they need to be replaced. Therefore, although the optical system has a simple configuration, it is made up of expensive parts, and these must be separately provided for maintenance, which is a factor that hinders the cost reduction of widespread use. Eliminating the correction plate has a great effect on reducing the cost of the optical system, but it creates an optical path difference between the two interfering bundles that is not for the purpose of measurement, and the optical path difference differs depending on the wavelength.

This poses a problem in that it causes complex measurement errors in the measurement results.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a low-cost, popular type Fourier transform spectrometer in which the beam splitting means is configured without a correction plate.

[Means for solving problems]

In this invention, the Fourier transform spectrometer is equipped with a calculation means for Fourier transform calculation, and the detection output, which is a function of optical path difference, is converted into a function of wave number, that is, wavelength, through Fourier transform calculation. By using
The present invention aims to correct errors based on optical path differences as a function of wavelength that occur in the beam splitting means, and to construct a beam splitting means that does not include a correction plate. In other words, the light beam splitting means is composed of only one transparent parallel plane plate with a thin film having almost the same transmittance and reflectance on one surface, and the calculating means uses the reflected light from the fixed reflecting mirror and the movable light beam. The detected output of the interference light with the reflected light from the reflecting mirror is subjected to Fourier cosine transform calculation and Fourier sine transform calculation, respectively, and the square root of the sum of the squares is calculated to obtain a wavelength or wave number function.

[Effect]

If the beam splitting means is composed of a single transparent plate with parallel surfaces on one side of which a thin film with approximately the same transmittance and reflectance is provided, the beam splitting means splits the beam and directs it toward the fixed reflector. There is an optical path difference xl between the light beam reflected from there and the light beam directed toward the movable reflector and reflected from there due to the movement of the movable reflector, which is equivalent to the light beam passing through the transparent plate twice. The optical path difference Δ(σ) as a function of the wave number to be added produces an optical path difference. Interferogram I obtained by detecting interference light of two light beams with this optical path difference
(xl is I (
xl= f B (a)e'2""-Δ(0ゝ'
da: f2(B ((Fl e-' 2πσΔ(σ1.
It is given by ei2πσxda. This relationship is also expressed as B 1crl e−' 2πσΔ(σ1== J”I
(xle-' 2πXσdx. The right side of the above equation is the interferogram 1 (since it is the Fourier transform of

Spectrum BN (
σ1 is BN (yl = B (crl e−' 2πσΔ(
σ). The above relationship is that the absolute value of BN(σ), which is a complex quantity, is equal to the absolute value of B(σ), and IBN
(σ11 = l BTσ)1. BN (H for σ1
N(a1=f I(xle-12"ddx=f 1[x
lcos2πxσdx -ifI(xlsin2πxcrdx) Therefore, taking the square root of the sum of the squares of the Fourier cosine transform f I (xi CO82πXσdx and the Fourier sine transform f This corresponds to taking the square root of the sum of squares of
This is to find the absolute value IBN(σ)1 of BN[σ1, and since IBN(σ1l=lBiσ11), 18(σ11, that is, a spectrum without the influence of the optical path difference in the beam splitting means) is obtained.

〔Example〕

FIG. 1 shows an embodiment of the invention.

A single transparent plane-parallel plate provided with a semi-transparent mirror film is processed in a light beam splitting means 432 in a Michelson interferometer according to a calculation procedure described below.

At point A on the translucent suture n, the optical path difference δ between the light reflected by the fixed reflector 4 and the light reflected by the movable reflector *5 is a function of the wavelength λ of the light beam. This wavelength function can also be treated as a function of the number of waves of wavelength λ arranged per unit length, that is, the wave number σ (= member). If the above optical path difference δ is expressed as a function δ(σ) of the wave number σ, it becomes ζ(σI=2(AXz-AXt)-2D(σ)(81). Here, AXI is the reflection between point A and the fixed reflector 4. The geometric distance to the plane, AX2 is the geometric distance between point A and the reflecting surface of the fixed reflecting mirror 5, and 2 (AX, -AX, ) is when there is no influence of the thickness of the parallel plane plate. It is equal to the optical path difference .

d is the thickness of the parallel plane plate. So 2D(σ)=Δ
(If σ1 is set, the optical path difference δCσ) is δfcrl = x − A (al
”).The interferogram I fxl obtained in this state is expressed as (Hxl = f B(crle i2π(FIX-Δ( c.
rl)d.

"f(B(σ)6-12ggΔja') et 2
πXσd0=f BH[crle””da
(11), where BN lσl = B (crl e −'2″'Δ
ta+ (12), (11
) and (5) and (6'), BN(cr
l = fooI (xl e-12” dx
(13), and the interferogram I
If ixl is directly converted into IJ, BN(σ) shown by equation (12) is obtained.

Equation (12) showing the relationship between BN(σ1 and B(σ)) uses a sine function and a cosine function.

BN ((Fl = B (al 6-2"'Δ"'
= BT(Fl e−1ψ(0)= B (σ) [c
osψlσl −i sin ψto)] (1
4). In other words, Equation (14) is: BN[σ) Each absolute value IBNIσ) 1 and the absolute value IB(σ) 1 of B(σ) are equal 1 Phase difference between them −ψ(σ) knee 2πσ right σ)
It shows that there is. Therefore, B(σ1) can be determined by determining IBN(σ)1 using the following procedure.

In this case, a finite value ±L is given to the upper and lower limits of the optical path difference as shown in Equation 71. Optical path difference δ(fl
fc If we give such a finite limit value.

Considering that the relationship between δ(σ1 and Define the maximum value Ll and minimum value L2 of X as given.As explained later, 1.-=1.+Δ(σmax)
.

L2=-L+Δ((Fmin).'maX*'
min is the maximum value and minimum value of the wave number of the target light, respectively.

Therefore, from equation (13), the real part PN(σ) of BNIσ) and the imaginary part QN(
σ) is given by the Fourier cosine transform and sine transform of I (xi, respectively. The spectrum B(σ) obtained from this is + IB(σ1l=lBNlσ'I = [PN21σl+Q
2N(σl) (18).

In other words, in the present invention, even if a phase difference occurs as a function of the wave number between the two beams due to the difference in the first passing medium in the beam splitting means of the Michelson interferometer, the interferogram obtained as the detector output is processed by the calculation unit Wt32. By taking the square root of the sum of the squares of the Fourier cosine transform and the Fourier sine transform in
(This is so that σ1 can be obtained.

When performing the above processing, assuming that the noise components of PN[σl, QN(σ) are ΔPN(σ) and ΔQN(σ1), BN(σ)
Since the noise ΔBN(σ) is as follows, it is shown that the positive and negative noise components do not cancel each other out, but always add their absolute values. However, the spectroscopic analyzer to which this invention is directed is aimed at being relatively inexpensive and not requiring very high resolution. The resolution referred to here is wave number resolution, and at this level, wave number resolution Δσ is given by Δσ=1/L(20). Here, L is the maximum optical path difference. For example, the resolution required for this type of spectrometer is Δσ=4cm−
', the required maximum optical path difference is L=1/Δσ=
It becomes 250 μm. This means that the movable reflector 5 is ±125 μm.
I agree with the decision to move it.

As will be described later, the movable reflecting mirror 5 is moved by ±227 μm, and the maximum optical path difference provided is larger than the above ±125 μm.1 However, with a normal incandescent light source, interference occurs even with an optical difference of several d. , Sakaki The coherence at the maximum optical path difference of μm is sufficient, and therefore the S/N ratio of the signal is sufficiently large. Therefore, even if a noise component ΔBNIσ) is added to the spectrum IBNIσ, it is sufficiently small compared to IBN(σ)1 and does not pose a problem.

Here, the optical path difference given to this device and the moving distance of the movable reflecting mirror 5 will be explained. In Figure 2, the wave numbers are σ and σmaX
+σmin optical path difference δ(σ1.
δ(0m2x) +δ(σmin), AX2 in Figure 1
x = 2 (AX2-A
This shows the relationship between X, ) and 1:AX2-AX.

σmaX tσm10 are the maximum and minimum values of the wave number of the light to be analyzed, respectively. As shown in equation (10), the optical path difference δ(σ1 is made up of a term X that does not depend on the wavenumber of light and a term Δ(σ1 that is dependent on the wavenumber), and when X=Δ(σ1, δ(σ1 = 0. Therefore, as shown in FIG.

The maximum optical path difference is ±L around this δ(σ1=0 position)
The interferogram I (xl) is obtained by moving the movable reflector 5 so that
21), and if δ(σ)=±L is given, then X=±L+Δ(σ)(22). That is, the movable reflector 5 is moved so that the difference in the geometric distances between the fixed reflector 4, the movable reflector 5, and the point A on the semi-transparent mirror film n becomes 10 of the above-mentioned X. In this case, since the value of Δ(σ1 differs depending on the wave number σ, the movement range of the movable reflector is determined in a first-order manner, and a limit value of at least ±L is given to δ(σ) for σ. do it like this.

From equation (22), X becomes the following for light with wave numbers of σmaX and eσmin. In general, the refractive index n(σ1 is n(amax
) > n (σm10), so from equation (9) D (amax ') > D ((Fmin)
(24) Therefore Δ(σl= 2
Due to the relationship D(σ), Δ(amax ) > Δ(σml
n ) (25). Considering the relationship of equation (25) in equation (23), the maximum value of
and the minimum value L2 is Ll=L+Δ(amax) (2
6) L2=-L+Δ((Fmin)
(27), and the range of
) ] (28). Therefore, the optical path difference given by the movement of the movable reflecting mirror 5 is −+ (Ll +L
Since the movement range is further centered around the point z),
The movable reflecting mirror 5 is AX2- AXI = + (Lt +
L2) is the center point. To these (9
), (26), (27), (ZB)17)
Applying each formula and the relationship 2D(σ)=Δ(σ), the center point of the stroke is AX2−AXl ” + (Lt→−L2 ) =+[Δ((Fmax
)+Δ(σmin) ]. If we set AXI:W, then AX2 at this point will be. Also, the stroke S is =±+(L+D(0m1x) D(0m1n))=±
It is given by +(L+, -(ζthing=Bian-9 books=ko).
(31) The parallel plane plate is a KBr plate with a thickness d of 3111, and the wavelength range of the light to be analyzed is from 2.5 μm to + μm.

If the required resolution is 4 crn-', then the wave number is G)
Amax = 1/2.5 Am = 4000 c
vt-', crmin='/20μg=5QQ
.

For the refractive index, n(σmax) = n (400
0) = 1.54.

n(0m1n)=n(500)=1.48. Δ(σma
X)-Δ(0m1n)=Δ(4000')-Δ(500
) = 408μtn, L = 250μ bait, so (
From formula 30), the stroke S of the movable reflex @5 is S = -
1=+(250+7') fim=±227 μm.

In the conventional technology, an optical path difference of ±250 μm is required to obtain a resolution of 4cIn-', and interferogram sampling is performed using He-N with a wavelength of 0.633 μm.
eThe number of sampling points is 250 if performed for each wavelength of laser light.
μm is 790 points in □X2. On the other hand, 0.63
There are 1440 points in 3 μm×2, and the number of numbering points is approximately 1.8 times. This results in an increase in memory in the computing unit, but ~ in reading the interferogram data.
1 word (= 2 bytes) is sufficient for the Φ conversion, so the amount of information is only on the order of 1440x2=2880 bits. This amount of increase in memory can be dealt with by adding inexpensive memory elements, so it has little effect on the price of the arithmetic device in the low-resolution device to which the present invention is applied.

Finally, it will be explained that the optical path difference caused by light passing through a parallel plane plate is expressed by equation (8).

FIG. 3 shows the path of light passing through a parallel plane board. It is reflected at point A on the semi-transparent mirror film and fixed reflection mirror 4
The geometrical optical path length in the parallel plane plate of light directed to AM is defined as f, K, and the optical path length in air equivalent to AM is defined as p(
σ), then p(σ'=v[crl AH (recommendation), where C is the speed of light in air, ■(C1 is the speed of light of wave number σ when visiting a parallel plane plate. The balls are parallel Since the refractive index of the plane plate is equal to n(σ), p(σ)=n(C1 penalty
(33). Further, the refraction angle θ of light incident on the parallel plane plate 26 at an incident angle □ of 45° is given by the law of refraction.

Therefore, if the equivalent optical path length in the air of the light reflected at point A and directed toward the fixed reflector 4 is 2, then e = AX + AB
' + pIσ) = AXI - AB cos a +
n (crlAB= AX+ + AB [n (
crl -cos ako (35)co
sα=cos(45'-θ): C0845°cosθ+5in45°sinθ.

Optical path difference δ (C1 is δ(σl:2(AX2 A) = 2(AX2-AXl)-2AB[n(crl-co)
sa] (38) Therefore (7), (36)
, (37), (38), Dtcrl=A
B[n(crl-cos a )],
(It is derived as follows: 33gv'2 f45=〒.

〔Effect of the invention〕

According to this invention, the wave number function, that is, the wavelength-dependent phase difference occurring between two light beams in the light beam splitting means of the Michelson interferometer in the Fourier transform infrared spectrometer is corrected by calculation. , the device can be constructed without using an expensive and deliquescent correction plate.

Moreover, in the arithmetic unit, an increase in the number of memories required for the correction calculation of one phase difference can be handled by adding an inexpensive memory element.

In addition to the above, not using a correction plate simplifies the configuration of the optical system, reduces the effort required for adjustment, and eliminates the need to always have a correction plate on hand as a maintenance component. This has a great effect on reducing prices, maintenance costs, and maintenance effort, and is effective in making it easier to provide popular Ha.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical system in an embodiment of the present invention, and FIG. 2 is a relational diagram comparing the optical path difference for light of different wave numbers and the movement range of a movable reflecting mirror. FIG. 3 is an explanatory diagram of the optical path difference that occurs in the beam splitting means,
FIG. 4 is a configuration diagram of an optical system according to the prior art. 1: Light source, 3.33: Michelin interferometer, 4: Fixed reflecting mirror, 5: Movable reflecting mirror, 6, 26: Parallel plane plate. 7.27: Semi-transparent mirror film, 9, 29: Luminous flux splitting means, 14
: Infrared photodetector, 22, 32: Arithmetic device. Figure 2

Claims (1)

[Scope of Claims] 1) A beam splitting means that splits the incident light into two beams; a fixed reflecting means that is fixed on the optical path of one of the split beams and reflects the beam onto the optical path; a movable reflecting means that reciprocates within a predetermined range on the optical path of the other luminous flux and reflects the luminous flux onto the optical path; a light detection means for detecting interference light that is incident on the means, overlaps and interferes, and is further split and emitted in a direction different from the two light beams, or the interference light, either directly or after being influenced by a sample, and the light; and a calculation means for inputting the output of the detection means as a function of the amount of movement of the movable reflection means and outputting it as a function of wave number or wavelength through Fourier transform calculation, wherein the beam splitting means is arranged on one surface. It is a single transparent parallel plane plate provided with a thin film having almost the same transmittance and reflectance, and the calculation means performs calculations for Fourier cosine transform, Fourier cosine transform, and Fourier sine transform of the output of the light detection means, respectively. 1. An interferometry spectrometer characterized in that after each calculation is performed, a calculation is performed to calculate the square root of the sum of squares of the results of each calculation. 2) An interference spectrometer according to claim 1, wherein the incident light is light in the infrared region. 3) In the device according to claim 1 or 2, the moving range of the movable reflecting means that provides a predetermined wave number resolution for monochromatic light is ±L, and the maximum and minimum wave numbers of the target light are σ_m_a_x and σ_m_i_n, the refractive index of the parallel plane plate for the light of these maximum and minimum wave numbers is n(σ_m_a_x) and n(σ_m_i_n),
If the thickness of the parallel plane plate is d, and the distance between the reflection point of the fixed reflection means and the incident point of the light beam on the thin film provided on the parallel plane plate is W, then the moving range of the movable reflection means is W + [d/(2√ 2)](√[2n^2(σ_m_a_
x)]+√[2n^2(σ_m_i_n)-1-2])
At least ±1/2{L+(d/√2){√[2n^2(σ_m_
a_x)-1]-√[2n^2(σ_m_i_n)-1
]}} An interference spectrometer characterized in that: 3) In the device according to any one of claims 1, 2, and 3, a transparent parallel plane plate provided with a thin film is arranged at an angle of 45° with the incident light. splits the incident light in the direction of incidence and in a direction perpendicular to that direction,
Furthermore, the interference spectrometer is characterized in that the interference light is emitted in a direction 180 degrees different from the perpendicular direction.