CN104165582A - Phase shift point-diffraction interference detection device and method based on reflecting grating - Google Patents

Abstract

The invention belongs to the technical field of optical interference detection, and in particular relates to a reflection grating-based phase shift point diffraction interference detection device and a detection method. A phase shift point diffraction interference detection device based on a reflective grating, including a light source, a collimated beam expander system, a window, an object to be measured, a first lens, a non-polarizing beam splitter, a reflective grating, a small hole mirror, a second lens, and an image sensor , the beam emitted by the light source is collimated and expanded by the collimator beam expander system, and the outgoing beam passes through the window and the object to be measured and then enters the first lens, and the beam focused by the first lens is divided into a beam of reference light by a non-polarizing beam splitter prism and a beam of object light; the reference light is irradiated on the pinhole mirror, and the object light is irradiated on the reflection grating. The device of the invention has low system complexity, simple structure, flexible and convenient operation, low cost, and does not need special optical elements such as polarizer groups.

Description

A reflection grating-based phase shift point diffraction interference detection device and detection method

technical field

The invention belongs to the technical field of optical interference detection, and in particular relates to a reflection grating-based phase shift point diffraction interference detection device and a detection method.

Background technique

Due to its unique characteristics of non-contact, high resolution, and no need for special treatment of samples, optical interferometry has been widely used in the detection of optical surfaces, deformation and thickness. The current optical interference detection structure can be divided into two types: separated optical path and common optical path: separated optical path interferometer, such as Tieman-Green interferometer, Mach-Zehnder interferometer, etc. Because the reference beam and the measurement beam interfere through different paths, it is easy to Affected by external vibrations, temperature fluctuations, etc. Compared with the separated optical path interferometer, the common optical path interferometer is not sensitive to external vibrations, temperature fluctuations, etc. because the reference beam and the measuring beam interfere through the same optical path, and has the advantages of strong anti-interference ability. field has received much attention. A typical structure of common optical path interferometer is point diffraction interferometer, but the early point diffraction interferometer has poor quantitative measurement ability. In order to make up for this shortcoming, domestic and foreign scholars have made many beneficial attempts.

Israeli scholar N.T.Shaked proposed a reflective off-axis point diffraction micro-interferometer (Shaked N.T. "Quantitative phase microscopy of biological samples using a portable interferometer," Opt.Lett., 37(11), 2016-2018(2012).) , a non-polarizing beam splitter is introduced into a standard 4f optical system to generate two beams of light, one of which is filtered by a reflective pinhole to form a reference light, and the other beam is reflected by a mirror and passes through a non-polarizing beam splitter Merge with the reference light again. This method only needs to collect one interferogram to obtain quantitative phase information, and the measurement efficiency is high. However, because of the off-axis structure, the spatial bandwidth and spatial sampling capability of the camera are sacrificed, which in turn limits the spatial resolution of the system and is easy to lose. The high-frequency information of the sample is measured.

Patent 201310206690.1 "A Reflective Point Diffraction Off-Axis Synchronous Phase-Shifting Interference Detection Device and Detection Method" introduces the light-splitting synchronous orthogonal phase-shift technology based on the polarization beam splitter prism, and obtains two orthogonal phase-shifts through one exposure acquisition. While improving the measurement efficiency, the measurement resolution of the system is improved, but the system is complex and the utilization rate of the field of view of the camera is low.

Guo Rongli of Xi'an Institute of Optics and Mechanics proposed a reflective point-diffraction coaxial micro-interferometer (R.Guo, B.Yao, P.Gao, J.Min, J.Zheng, T.Ye. "Reflective Point- diffraction microscope interferometer with long term stability."COL 2011,9(12):120002.), through the introduction of polarization phase shift technology, four phase shifted interferograms are collected in time sequence, and the utilization rate of the field of view is high, but because at least 4 pieces are used The polarizing element realizes the phase shift, and the system complexity is high.

Contents of the invention

The purpose of the present invention is to provide a phase shift point diffraction interference detection device based on reflection grating.

The purpose of the present invention is also to provide a reflection grating-based phase shift point diffraction interference detection method.

The purpose of the present invention is achieved like this:

A phase shift point diffraction interference detection device based on a reflective grating, including a light source, a collimated beam expander system, a window, an object to be measured, a first lens, a non-polarizing beam splitter, a reflective grating, a small hole mirror, a second lens, and an image sensor , the beam emitted by the light source is collimated and expanded by the collimator beam expander system, and the outgoing beam passes through the window and the object to be measured and then enters the first lens, and the beam focused by the first lens is divided into a reference beam by a non-polarizing beam splitter prism and a beam of object light; the reference light is irradiated on the small hole mirror, and the object light is irradiated on the reflection grating; the reflected object light and reference light are combined into a beam after passing through the non-polarizing beam splitter again, and then passed through the second lens After that, the interferogram is generated, and it is collected by the image sensor into the computer at the same time.

The small hole mirror is located on the focal plane of the first lens, and the reflection grating is located on the focal plane of the second lens.

A reflective grating can be moved slightly laterally to create a phase shift.

The +1 diffraction order light from the reflective grating is used to generate the interferogram.

The diameter of the reflective area of the pinhole mirror is d _p ≤ 1.22λf ₁ /D, where λ is the wavelength of the light source, f ₁ is the focal length of the first lens, and D is the diameter of the window.

Between the object to be measured and the first lens, a microscopic objective lens and a correction objective lens can also be placed in sequence.

A phase shift point diffraction interference detection method based on a reflective grating, comprising the following steps:

(1) Adjust the light source so that the light beam emitted by the light source passes through the collimated beam expander system, the window, the object to be measured, the first lens and the non-polarizing beam splitter in turn to form focused object light and reference light, which are respectively After reflection, the reflective grating and the pinhole mirror pass through the non-polarizing beam splitter and the second lens to form an interference pattern, which is collected by the image sensor and transmitted to the computer;

(2) The reflective grating is driven to produce a series of lateral displacements Δ=(k-1)d/N, the interferogram collected by the image sensor will be introduced into a series of phase shifts δ _k =(k-1)2π/N, and its corresponding intensity distributed as

Among them, k=1,2,...,N, O is the light field distribution of the object light, R is the light field distribution of the reference light, is the phase distribution of the object to be measured;

Using the least square method, the phase distribution of the object to be measured can be obtained as

The beneficial effects of the present invention are:

1. The present invention combines the reflective point diffraction interference method with the reflective grating phase-shifting technology, and completes the recovery of the phase to be measured by collecting a series of phase-shifted interferograms, ensuring the anti-interference ability and resolution of the system and the utilization rate of the image sensor field of view Based on this, the accuracy of phase shift is improved and the complexity of phase shift is simplified;

2. The system complexity of the device of the present invention is low, the structure is simple, the operation is flexible and convenient, the cost is low, and special optical elements such as polarizer groups are not required;

3. By introducing a microscope objective lens, the method can be applied to microscopic measurement.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the phase shift point diffraction interference detection device based on the reflective grating;

2 is a schematic diagram of the principle of a phase-shift point diffraction micro-interference detection device based on a reflection grating;

Figure 3(a) is the first phase shift interferogram collected by computer;

Fig. 3 (b) is the second phase shift interferogram collected by computer;

Figure 3(c) is the third phase-shifted interferogram collected by computer;

Figure 3(d) is the fourth phase-shifted interferogram collected by computer;

Figure 4 shows the phase distribution according to the object to be measured Recover the obtained phase distribution of the object to be measured.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The reflective grating-based phase-shift point diffraction interference detection device of the present invention includes a light source, a collimated beam expander system, a window, an object to be measured, a first lens, a non-polarizing beam splitter, a reflective grating, a small hole reflector, a second Two lens, image sensor,

The light beam emitted by the light source is collimated and expanded by the collimator beam expander system, and then the outgoing beam passes through the window and the object to be measured and then enters the first lens. The beam focused by the first lens is divided into a beam of reference light and A beam of object light; the reference light is irradiated on the small hole mirror, and the object light is irradiated on the reflection grating; the reflected object light and reference light are combined into a beam after passing through the non-polarizing beam splitter again, and then pass through the second lens An interferogram is generated and simultaneously captured by an image sensor into a computer.

The pinhole mirror is located on the focal plane of the first lens, and the reflective grating is located on the focal plane of the second lens.

A reflective grating can be moved slightly laterally to create a phase shift.

The +1 diffraction order light from the reflective grating is used to generate the interferogram.

The diameter of the reflective area of the pinhole mirror is d _p ≤ 1.22λf ₁ /D, where λ is the wavelength of the light source, f ₁ is the focal length of the first lens, and D is the diameter of the window.

Between the object to be measured and the first lens, a microscopic objective lens and a correction objective lens can also be placed in sequence for microscopic measurement.

Based on the interference detection method of the above-mentioned interference detection device, its realization process is as follows:

①. Adjust the light source so that the beam emitted by the light source passes through the collimated beam expander system, the window, the object to be measured, the first lens and the non-polarizing beam splitter in sequence to form a focused object light and reference light, which are respectively After reflection, the reflective grating and the pinhole mirror pass through the non-polarizing beam splitter and the second lens to form an interference pattern, which is collected by the image sensor and transmitted to the computer;

② Assuming that the reflective grating is driven to produce a series of lateral displacements Δ=(k-1)d/N, the interferogram collected by the image sensor will be introduced into a series of phase shifts δ _k =(k-1)2π/N, and its corresponding intensity distributed as

Among them, k=1,2,...,N, O is the light field distribution of the object light, R is the light field distribution of the reference light, is the phase distribution of the object to be measured.

Using the least square method, the phase distribution of the object to be measured can be obtained as

The specific embodiment of the present invention is described below in conjunction with Fig. 1, and the phase shift point diffraction interference detection device based on the reflective grating described in this embodiment includes a light source 1, a collimated beam expander system 2, a window 3, an object to be measured 4, a first A lens 5 , a non-polarizing beamsplitter prism 6 , a reflective grating 7 , a small hole reflector 8 , a second lens 9 , and an image sensor 10 . Wherein, the light source 1 adopts a He-Ne laser with a wavelength of 632.8nm, or other monochromatic visible light sources, and the wavelength can be selected according to needs. The focal lengths of the first lens 5 and the second lens 9 are the same, both being f ₁ =f ₂ =250mm. The small aperture mirror 8 is located on the focal plane of the first lens 5 , and the reflective grating 7 is located on the focal plane of the second lens 9 . The period d of the reflective grating 7 is 54.72um, and it can move slightly laterally to generate a phase shift. The diameter of the reflective area of the small hole reflector 8 is d _p ≤ 1.22λf ₁ /D (D is the window diameter). Between the object 4 to be measured and the first lens 5, a microscopic objective lens and a correction objective lens can also be placed in sequence.

Utilize above-mentioned phase-shift point diffraction interference detection device based on reflection grating, the specific embodiment of detection method of the present invention is as follows:

First, adjust the entire optical system before detection, turn on the light source 1, the beam emitted by the light source is collimated and expanded by the collimator beam expander system 2, and the outgoing beam passes through the window 3 and the object to be measured 4 and then enters the first lens 5. The light beam focused by the first lens 5 is divided into a beam of object light and a beam of reference light by the non-polarizing beam splitter prism 6, the reference light is irradiated on the small hole reflector 8, the object light is irradiated on the reflection grating 7, and the reflected object light and the reference light are merged by the non-polarizing beam splitter prism 6 again, and then pass through the second lens 9 in turn to generate an interference pattern, which is collected by the image sensor 10 and collected in the computer;

After recording the first interferogram I ₁ , translate the reflective grating 7, and each small displacement in the process of translating the reflective grating three times is d/4 (d is the period of the reflective grating). The phase shifts introduced by the movement are π/2, π, 3π/2, respectively, and the interferograms are recorded sequentially. In this way, four interferograms I ₁ , I ₂ , I ₃ and I ₄ are obtained through four exposures for phase recovery of the object to be measured. The phase to be measured is calculated by the following formula:

This implementation example has very good stability, the phase shift between the interference patterns required for phase recovery is accurate, and because the recovery algorithm is simple, the complexity of the system is further reduced.

Claims (7)

1. A phase shift point diffraction interference detection device based on a reflective grating, comprising a light source (1), a collimated beam expander system (2), a window (3), an object to be measured (4), a first lens (5), Non-polarizing beam splitting prism (6), reflective grating (7), pinhole reflector (8), second lens (9), image sensor (10), characterized in that: the light beam emitted by the light source (1) is collimated and expanded The beam system (2) collimates and expands the outgoing beam to the first lens (5) after passing through the window (3) and the object to be measured (4), and the beam focused by the first lens (5) is split by non-polarization The prism (6) is divided into a beam of reference light and a beam of object light; the reference light is irradiated on the small hole reflector (8), and the object light is irradiated on the reflection grating (7); the reflected object light and reference light pass through the non- After the polarization beam splitting prism (6) merges into a bundle of light beams, the interference pattern is generated after passing through the second lens (9), and is collected into the computer by the image sensor (10) at the same time. 2. a kind of phase-shift point diffraction interference detection device based on reflection grating according to claim 1, is characterized in that: described pinhole reflector (8) is positioned on the focal plane of first lens (5), so The reflective grating (7) is located on the focal plane of the second lens (9). 3. A reflective grating-based phase-shift point diffraction interference detection device according to claim 1 or 2, characterized in that: the reflective grating (7) can be slightly moved laterally to generate a phase shift. 4. The reflective grating-based phase shift point diffraction interference detection device according to claim 1, 2 or 3, characterized in that: the +1 diffraction order light of the reflective grating (7) is used to generate an interferogram. 5. The phase-shift point diffraction interference detection device based on reflection grating according to claim 1 or 2, characterized in that: the reflection area diameter of the small hole mirror (10) is _{dp≤1.22λf 1} /D, Wherein, λ is the wavelength of the light source (1), f ₁ is the focal length of the first lens (5), and D is the diameter of the window (3). 6. The reflective grating-based phase shift point diffraction interference detection device according to claim 1, characterized in that: a microscopic objective lens can also be placed sequentially between the object to be measured (4) and the first lens (5) (11) and correction objective lens (12). 7. A phase shift point diffraction interference detection method based on reflection grating, is characterized in that, comprises the steps: (1) Adjust the light source so that the light beam emitted by the light source passes through the collimated beam expander system, the window, the object to be measured, the first lens and the non-polarizing beam splitter in turn to form focused object light and reference light, which are respectively After reflection, the reflective grating and the pinhole mirror pass through the non-polarizing beam splitter and the second lens to form an interference pattern, which is collected by the image sensor and transmitted to the computer; (2) The reflective grating is driven to produce a series of lateral displacements Δ=(k-1)d/N, the interferogram collected by the image sensor will be introduced into a series of phase shifts δ _k =(k-1)2π/N, and its corresponding intensity distributed as Among them, k=1,2,...,N, O is the light field distribution of the object light, R is the light field distribution of the reference light, is the phase distribution of the object to be measured; Using the least square method, the phase distribution of the object to be measured can be obtained as