JP2001343321A - Method for measuring cross sectional image of measuring sample and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the spatial resolution in the direction of optical axis to achieve high sensitivity and high spatial resolution when measuring the cross sectional image of a measuring sample. SOLUTION: This device for measuring the cross sectional image of a measuring sample is provided with a light source 1, the measuring sample 5 irradiated with light waves from the light source 1 coming through a beam splitter 3 and an objective lens 4, a one-dimensional array light detector 10 and a signal processor 13. Signal light 21 which is back scattering light from the sample 5 enters the detector 10 through the objective lens 4, the beam splitter 3 and a biprism 9 and reference beam 22 enters the detector 10 through mirrors 7, 8 and the biprism 9 after passing through the beam splitter 3 and a phase modulator 6 for heterodyne detection to generate a spatial interference intensity pattern by an angle 2θ formed by the signal light 21 and the reference beam 22. The processor 13 changes the spatial interference intensity pattern with modulation frequency (f) of the phase modulator 6 with respect to time and has a memory for storing the spatial interference intensity pattern as one-dimensional distribution of beam amplitude. A space interference intensity value is raised to the N-th power, and whole amplitude of its half value is narrowed to substantially N-1/2 to improve the spatial resolution in the direction of optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a cross-sectional image of a measurement sample and a device therefor, and more particularly to a cross-sectional image measurement by spatial interference signal processing using a heterodyne detection method.

[0002]

2. Description of the Related Art Conventionally, there have been the following techniques disclosed in such fields.

In a tomographic image measuring method using known spatial interference, a reflection point in a sample is identified from the envelope shape measurement of the interference intensity pattern, and a tomographic image is measured. That is, the reflection point is identified by measuring the shape of the envelope of the interference intensity pattern, and the width of the envelope is the spatial resolution.

[0004]

As described above, conventionally, from the measurement of the shape of the envelope of the interference intensity pattern,
There is a problem that the reflection point is identified, the width of the envelope is the spatial resolution, and the resolution is low.

That is, in the conventional optical coherence tomography (OCT), the coherence length is the limit of the spatial resolution.

The present invention provides a method and apparatus for measuring a cross-sectional image of a measurement sample, which can eliminate the above-mentioned problems, improve the spatial resolution in the optical axis direction, and achieve high sensitivity and high spatial resolution. The purpose is to do.

[0007]

In order to achieve the above object, the present invention provides: [1] by alternately performing measurement of the backscattered light intensity profile in the optical axis direction and scanning in the lateral direction with respect to the optical axis. In the method for measuring the cross-sectional image of the measurement sample, the spatial interference intensity distribution is measured using a heterodyne detection method, the spatial interference intensity value is raised to the Nth power, the full width at half maximum is reduced to approximately 1 / √N, and the optical axis direction is reduced. It is characterized in that the spatial resolution is improved by approximately N times.

[2] In the method for measuring a cross-sectional image of a measurement sample according to the above [1], the spatial interference intensity value is set to the fourth power,
The spatial resolution in the optical axis direction is 4.7 μm.

[3] In an apparatus for measuring the cross-sectional image of a measurement sample by alternately performing measurement of the backscattered light intensity profile in the optical axis direction and scanning in the lateral direction with respect to the optical axis, a light source and a light wave from the light source A measurement sample irradiated through the splitter and the objective lens, and signal light that is backscattered light from the measurement sample enters through the objective lens, the beam splitter and the biprism, and the reference light is transmitted through the beam splitter. A one-dimensional array light detecting device that, after passing through a phase modulator for heterodyne detection, enters through a mirror and the biprism and generates a spatial interference intensity pattern by an angle 2θ between the signal light and the reference light; When the modulation frequency of the phase modulator is f and the spatial interference intensity pattern is temporally changed at the frequency f, A signal processing device having a memory for storing a one-dimensional distribution of beat amplitudes, and the spatial interference intensity value raised to the Nth power, the full width at half maximum thereof is reduced to approximately 1 / √N, and the spatial resolution in the optical axis direction is substantially reduced. Means for increasing the ratio to 1 / √N.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic view of a cross-sectional image measuring apparatus using spatial interference signal processing using a heterodyne detection method according to an embodiment of the present invention.

In this figure, 1 is a light source, 2 is a lens,
3 is a beam splitter (BS), 4 is an objective lens (O
BJ), 5 is a measurement sample (S), 6 is a phase modulator (P
M), 7 is a first mirror (M1), 8 is a second mirror (M2), 9 is a biprism (BP), 10 is a one-dimensional array photodetector (AD), 11 is a scanning device (SS). , 1
Reference numeral 2 denotes a detection + filter device (RF), and reference numeral 13 denotes a signal processing device (PC).

The basic principle of the present invention will be described below with reference to FIG.

A light wave from the light source 1 passes through a beam splitter (BS) 3 and an objective lens (OBJ) 4 and irradiates a measurement sample 5. The signal light 21, which is the backscattered light from the measurement sample 5, passes through the objective lens (OBJ) 4, the beam splitter (BS) 3, and the biprism (BP) 9 again, and the one-dimensional array light detection device (AD) 10. Incident on.

On the other hand, the reference beam 22 is supplied to a beam splitter (BS) 3 and a phase modulator (PDP) for heterodyne detection.
After passing through M) 6, the light enters a one-dimensional array photodetector (AD) 10 via a first mirror (M1) 7, a second mirror (M2) 8, and a biprism (BP) 9.

Then, a spatial interference intensity pattern is generated on the one-dimensional array photodetector (AD) 10 by the angle 2θ between the signal light 21 and the reference light 22. Phase modulator (PM) 6
If the modulation frequency of f is f, the intensity pattern temporally changes at the frequency f. One-dimensional array photodetector (AD) 1
Numeral 0 denotes an array of photodetectors in which M photodetectors are arranged one-dimensionally. The scanning device (SS) 11 is first connected to the photodetector of the first channel. At this time, after the heterodyne beat signal of the frequency f from the photodetector is input and stored in the signal processing device (PC) 13 via the detection + filter device (RF) 12, the scanning device (SS) 11 , And all the photodetectors are connected for each channel by repeating in order, and the one-dimensional spatial interference intensity pattern is stored as a one-dimensional distribution of the beat amplitude in the memory of the signal processing device (PC) 13. Realize on top.

For example, a spatial interference pattern by a reference point a in a sample having an optical path equal to the reference optical path and a point b separated by ΔZ is represented by the following equations (1) to (3), and is shown in FIG.
As shown in (a), there are two wave packets having a DC component.

In FIG. 2A, l _C = 4
l _n ² λ ² / πΔλ, 2x ₀ = l _C / 2sin θ, x _S
= Δz / sin θ and λ ′ = λ / 2 sin θ.

[0019]

(Equation 1)

[0020]

(Equation 2)

[0021]

(Equation 3)

Where I _R : reference light intensity, I _Sa : backscattered light intensity from point a, I _Sb : backscattered light intensity from point b, ω ₀ = 2πc / λ: angular frequency of light, δ = πcΔλ /
^{_{√ (2l n 2) λ 2}} : spectrum spread parameters, φ
₀ : modulation index of phase modulation, f: phase modulation frequency, Δz:
X is the distance from the reference point a to point b, which is ΔZ away from the reference point, and x is the distance from the center position on the one-dimensional array photodetector.

Here, λ ′, 2x ₀ and x _S are respectively
It corresponds to the shift of the wave packet due to the period of the interference, the width of the wave packet, and the distance between the reference point and an arbitrary scattering point.

The amplitude distribution of the heterodyne beat signal measured via the detection + filter device (RF) 12 is shown in FIG.
As shown in (b), this is an envelope from which the background has been removed, and represents only a coherent scattered light signal from within the sample. The width of the wave packet at this time is 2x
₀ and the spatial resolution is half the coherent length.

This amplitude distribution information is stored in a signal processor (P
C) Since the intensity signal value is stored in the memory 13, the intensity signal value is raised to the Nth power. The intensity distribution when raised to the Nth power is as shown in FIG. 2C, and the full width at half maximum is reduced to approximately 1 / √N.
This means that the spatial resolution in the optical axis direction has been improved by approximately ΔN times.

According to the above-described method, the tomographic image can be measured by alternately performing the measurement of the backscattered light intensity profile in the optical axis direction and the horizontal scanning with respect to the optical axis.

As a specific example, a light source wavelength: 0.8 μm,
Spectral width: 30 nm, array detector pitch: 25 μ
m, array length: 25.6 mm. At this time, the coherence length is 18.8 μm, and the spatial resolution in the optical axis direction is 9.4 μm. Since the period of the interference pattern is 50 μm from the sampling theorem, each 2θ formed by the signal light and the reference light is 1.8 °. At this time, the measurement range in the sample is 410 μm, and assuming fourth-order signal processing, the spatial resolution in the optical axis direction is 4.7 μm.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0029]

As described above, according to the present invention, the following effects can be obtained.

(A) In measuring a cross-sectional image of a measurement sample,
High sensitivity and a dynamic range are realized by using a heterodyne detection method for the spatial interference intensity distribution measurement, and the spatial resolution can be improved by approximately ΔN times by N-th signal processing.

(B) It becomes possible to measure tomographic images with high spatial resolution, and new clinical diagnosis is expected in the medical field.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cross-sectional image measurement apparatus using spatial interference signal processing using a heterodyne detection method, showing an embodiment of the present invention.

FIG. 2 is a diagram showing a wave packet by a cross-sectional image measuring apparatus by spatial interference signal processing using a heterodyne detection method according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 light source 2 lens 3 beam splitter (BS) 4 objective lens (OBJ) 5 sample to be measured (S) 6 phase modulator (PM) 7 first mirror (M1) 8 second mirror (M2) 9 biprism (BP) 10) One-dimensional array photodetector (AD) 11 Scanner (SS) 12 Detector + Filter (RF) 13 Signal processor (PC) 21 Signal light 22 Reference light

 ──────────────────────────────────────────────────続 き Continuation of the front page F term (reference) 2F065 AA54 BB05 DD03 FF42 FF51 GG01 JJ02 JJ25 LL12 LL46 LL47 MM16 NN08 QQ17 QQ28 2G059 AA05 EE02 EE09 FF01 GG09 JJ11 JJ13 JJ22 JJ30 NN01 KK04 MM04

Claims (3)

[Claims] 1. A method for measuring a cross-sectional image of a measurement sample by alternately performing measurement of a backscattered light intensity profile in an optical axis direction and scanning in a lateral direction with respect to the optical axis, wherein: (a) spatial interference using a heterodyne detection method; (B) cross-section of the measurement sample, wherein (b) the spatial interference intensity value is raised to the Nth power and the full width at half maximum is reduced to approximately 1 / √N to improve the spatial resolution in the optical axis direction. Image measurement method. 2. A cross-sectional image of a measurement sample according to claim 1, wherein the spatial interference intensity value is a fourth power and the spatial resolution in the optical axis direction is 4.7 μm. Measuring method. 3. An apparatus for measuring a cross-sectional image of a measurement sample by alternately performing measurement of a backscattered light intensity profile in an optical axis direction and scanning in a lateral direction with respect to the optical axis, wherein: (a) a light source; (C) signal light, which is backscattered light from the measurement sample, is incident through the objective lens, the beam splitter, and the biprism. Together, the reference light is the beam splitter,
After passing through a phase modulator for heterodyne detection, is incident through a mirror and the biprism, and by an angle 2θ between the signal light and the reference light, a one-dimensional array light detection device that generates a spatial interference intensity pattern, (D) a signal processing device having a memory for changing the spatial interference intensity pattern over time with the frequency f, where f is the modulation frequency of the phase modulator, and for storing a one-dimensional distribution of beat amplitudes; A means for raising the spatial interference value to the Nth power, reducing the full width at half maximum thereof to approximately 1 / √N, and improving the spatial resolution in the optical axis direction.