A dual-channel polarization carrier phase shift common-path digital holographic measurement device and method

Abstract

This invention discloses a dual-channel polarized carrier phase-shift common-path digital holographic measurement device and method, comprising a light source, a collimation and beam-expanding system, a first polarizer, a quarter-glass slide, a rectangular aperture, a first lens, a polarizing beam splitter, a second lens, a second polarizer, a CCD camera, and a computer. The light beam emitted from the light source is collimated and expanded into a planar beam by the beam-expanding system. After passing through the first polarizer, it becomes 45° linearly polarized light, reaching the rectangular aperture. The half-beam carrying object information propagates in a 45° linearly polarized state through the window where the sample is placed, while the other half-beam carrying no sample information propagates in a circularly polarized state. The beams propagate to the first lens, where the polarizing beam splitter replicates the beam into two mirror-image beams. These beams then propagate to the second lens, pass through the second polarizer, and are captured by the CCD camera as two carrier holograms, which are then transmitted to the computer. This invention features a compact structure, simple operation, fewer acquisition cycles, and high imaging resolution.

Description

Technical Field

[0001] This invention belongs to the field of digital holographic measurement and relates to a dual-channel polarization carrier phase shift common-path digital holographic measurement device and method. Background Technology

[0002] Phase-shifting digital holography, due to its advantages of rapid, non-destructive, and high-precision full-field measurement, is widely used in fields such as micro / nano device detection, 3D imaging, surface morphology measurement, and cell refractive index measurement. However, existing phase-shifting digital holography techniques require complex optical path structures and high-precision phase-shifting devices, resulting in bulky structures and high operational difficulty. Furthermore, multiple acquisitions are often required during sample measurement, which significantly limits the measurement of dynamic samples. Off-axis digital holography suffers from low spatial bandwidth utilization during phase retrieval due to interference from zero-order terms during effective information extraction, thus reducing imaging resolution. Therefore, phase-shifting digital holographic measurement devices that are compact, simple to operate, require fewer acquisitions, and offer high imaging resolution have attracted widespread attention from scholars both domestically and internationally.

[0003] Gao et al. (Peng Gao, Irina Harder, Vanusch Nercissian, Klaus Mantel, and Baoli Yao, "Phase-shifting point-diffraction interferometry with common-path and in-line configuration for microscopy," Opt. Lett. 35, 712-714 (2010)) proposed a common-path coaxial phase-shifting point diffraction microscopy apparatus. This apparatus introduces a double grating into the point diffraction interferometer, which allows the reference light and object light to propagate along the same path while obtaining the reference light through pinhole filtering. This overcomes the interference of the external environment and improves the spatial bandwidth product of the CCD. However, it is difficult to eliminate the additional phase difference in the spatial carrier frequency caused by vibration when using the step phase-shifting method.

[0004] Roitshtain et al. (Roitshtain D, Turko NA, Javidi B, Shaked NT, "Flipping interferometry and its application for quantitative phase microscopy in a micro-channel", Opt. Lett. 41, 2354 (2016)) proposed an off-axis digital holographic microscopy device based on flipping interferometry. This device uses a reflecting mirror to reverse the beam, thereby achieving coincident interference between the object beam and the reference beam to obtain a carrier hologram. However, this holographic technique is derived from a Michelson interferometer, and the object beam and reference beam are still partially separated. Moreover, this technique belongs to traditional off-axis digital holography, and the zero-order image will affect the extraction of the real image, thus reducing the resolution of the reconstruction result.

[0005] Zhang Wenxi et al. from the Chinese Academy of Sciences proposed a multi-frame phase-shifting digital holography method and device, such as CN105404128A. This device uses two acousto-optic modulators to modulate the object light and reference light respectively to generate low-frequency heterodyne, thereby obtaining multi-frame phase-shifting carrier holograms, eliminating the influence of twin images and reducing the interference of random noise. However, this device has many components, a complex structure, and uses a beam splitter, making it relatively sensitive to disturbances in the external environment. The multi-frame acquisition method is not suitable for measuring dynamic objects. Summary of the Invention

[0006] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a dual-channel polarization carrier phase shift common-path digital holographic measurement device and method that is compact in structure, simple in operation, requires fewer acquisitions, and has high imaging resolution.

[0007] To solve the above-mentioned technical problems, the present invention provides a dual-channel polarization carrier phase-shift common-path digital holographic measurement device, comprising: a light source with wavelength λ, a collimation and beam expanding system, a first polarizer, a quarter-glass slide, a rectangular aperture, a first lens, a polarizing beam splitter, a second lens, a second polarizer, a CCD camera, and a computer; the light beam emitted from the light source forms a planar beam after passing through the beam expanding and collimating system, and then becomes linearly polarized light at 45° after passing through the first polarizer, subsequently reaching the rectangular aperture. The half-beam carrying object information continues to propagate in a 45° linearly polarized state through the window where the sample is placed, and then passes through the quarter-glass slide. The beam in half of the window, without sample information, propagates in a circularly polarized state. The beam travels along the same path to the first lens, and after passing through the polarizing beam splitter, it is replicated into two mirror-image beams. These beams continue to travel along the same path to the second lens, and then, after passing through the second polarizer, two phase-shifted carrier holograms are simultaneously acquired on the CCD camera and transmitted to the computer. The first and second lenses constitute a 4f system, with the sample under test and the quarter-slide placed in the two windows of the rectangular aperture, respectively. Both the first and second polarizers are placed perpendicular to the optical axis. The CCD camera is placed on the back focal plane of the second lens.

[0008] Furthermore, the polarizing beam splitter is placed at a 45° angle to the optical axis, 1-2 cm in front of the Fourier plane of the first lens.

[0009] The present invention also includes a measurement method using the above-mentioned dual-channel polarization carrier phase shift common-path digital holographic measurement device, comprising:

[0010] Step A: After passing through the first polarizer, the light source reaches the rectangular aperture, forming an object beam with a 45° linear polarization state and a reference beam with a circular polarization state. The beam is then copied into two mirror-image beams by a polarizing beam splitter at a 45° angle to the optical axis.

[0011] Step B: Interfere the linearly polarized reference light with 45° and the circularly polarized object light, and after polarization modulation, capture two carrier holograms with π / 2 phase shift in one go by a CCD camera;

[0012] Step C: Recover the original light field of the target based on the two carrier holograms.

[0013] Furthermore, the two mirror-image beams described in step A satisfy the following:

[0014]

[0015]

[0016] Where W(x,y) represents a rectangular window of size H×L, AP represents the center-to-center distance between two windows, and A R and A OThese represent the reference beam and the object beam, respectively. This indicates the phase of the object being measured.

[0017] Furthermore, the two carrier holograms with a phase shift of π / 2 described in step B satisfy the following:

[0018]

[0019]

[0020] Where W(x,y) represents a rectangular window of size H×L, AP represents the center-to-center distance between two windows, and A R and A O These represent the reference beam and the object beam, respectively. represents the phase of the object under test, and f represents the carrier wave size.

[0021] Furthermore, step C, which involves recovering the original light field of the target based on the two carrier holograms, includes:

[0022] The zero-order image is removed by subtracting the two carrier holograms obtained in step B:

[0023]

[0024] Among them, A R and A O These represent the reference beam and the object beam, respectively. represents the phase of the object under test, and f represents the carrier wave size.

[0025] Then, phase recovery is performed using a phase recovery algorithm based on Fourier transform:

[0026]

[0027] Where FT stands for Fourier transform, IFT stands for inverse Fourier transform, and BPF stands for bandpass filter;

[0028] After acquiring a hologram without a sample and performing the above operations, the following result is obtained:

[0029]

[0030] Where I′ represents a hologram without a sample;

[0031] Finally, the background phase and space carrier are removed by division to obtain the phase of the measured object:

[0032]

[0033] The beneficial effects of this invention are:

[0034] 1. Based on the 4f structure, polarization phase shift technology and polarization beam splitting technology are introduced to obtain two carrier holograms with π / 2 phase shift at one time, avoiding multiple phase shifts and the environmental changes caused by multiple phase shifts, such as vibration and adjustment errors.

[0035] 2. By obtaining two phase-shifted carrier holograms, interference from the zero-order image can be effectively eliminated, and the high-quality original object light field can be recovered through a simple algorithm, providing a practical solution for real-time recording of high-speed motion processes.

[0036] The device of the present invention has the following significant features:

[0037] 1. The device of the present invention has a simple and compact structure, low system positioning complexity requirements, and is easy to adjust. It does not require any special optical components such as gratings, pinholes, or corner mirrors, and has low cost.

[0038] 2. The device of the present invention adopts a common optical path structure, which has strong anti-interference ability and good stability. Attached Figure Description

[0039] Figure 1 Schematic diagram of a dual-channel polarization carrier phase shift common-path digital holographic measurement device;

[0040] Figure 2 This is a carrier hologram obtained in this embodiment of the device;

[0041] Figure 3 This is a spectrum obtained from an embodiment of the device.

[0042] Figure 4 A three-dimensional image schematic diagram provided for an embodiment of this device. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] Figure 1 In the diagram, the numbers are as follows: 1-light source, 2-collimating and expanding beam system, 3-first polarizer, 4-rectangular aperture, 5-sample under test, 6-quarter glass slide, 7-first lens, 8-polarizing beam splitter, 9-second lens, 10-second polarizer, 11-CCD camera, and 12-computer.

[0045] Combination Figure 1A dual-channel polarized carrier phase-shift common-path digital holographic measurement device includes a light source with wavelength λ, a sample under test, a collimation and beam-expanding system, a first polarizer, a quarter-glass slide, a rectangular aperture, a first lens, a polarizing beam splitter, a second lens, a polarizer, a CCD camera, and a computer. The light beam emitted from the light source forms a planar beam after passing through the beam-expanding and collimating system. After passing through the first polarizer, it becomes linearly polarized light at 45°, then reaches the rectangular aperture. The half-beam passing through the window where the sample is placed carries object information and continues to propagate in a 45° linearly polarized state. The half-beam passing through the window where the quarter-glass slide is placed has no sample information and propagates in a circularly polarized state. Both beams propagate along the same path to the first lens. After passing through the polarizing beam splitter with an inclined angle, the beam is replicated into two mirror-image beams, which continue to propagate along the same path to the second lens. After passing through the polarizer, two phase-shifted carrier holograms can be simultaneously acquired on the CCD camera. Finally, the data is uploaded to the computer via a USB port. The first and second lenses form a 4f system; the object and the quarter-wave plate are placed in the two windows of the rectangular aperture, respectively; the first and second polarizers are both placed perpendicular to the optical axis; the polarizing beam splitter is placed at a 45° angle to the optical axis 1-2 cm in front of the Fourier plane of the first lens; the CCD camera is placed on the back focal plane of the second lens.

[0046] The dual-channel polarized carrier phase-shift common-path digital holographic measurement device is implemented as follows: An optical system is built according to the schematic diagram. A light beam with wavelength λ is emitted from a light source. After passing through a beam expander and collimator system to form a planar beam, it sequentially passes through a first polarizer with a 45° linear polarization state, a rectangular aperture containing a quarter-glass slide and the sample to be measured to form an object beam with a circular polarization state and a reference beam with a 45° linear polarization state. Then, it passes through a first lens and a tilted polarizing beam splitter. The tilted 45° polarizing beam splitter replicates the beam into two mirror-image beams. Subsequently, a second lens, a second polarizer, and a CCD camera are used to finally form two carrier holograms with a phase difference on the CCD camera.

[0047] Combination Figure 1 A schematic diagram of a dual-channel polarization carrier phase shift common-path digital holographic measurement device. The measurement method includes the following steps:

[0048] Step A: After passing through the beam expander and collimator system, the light source passes through the first polarizer and reaches the rectangular aperture, forming an object beam with a 45° linear polarization state and a reference beam with a circular polarization state. The beam is then copied into two mirror-image beams by a polarizing beam splitter at a 45° angle to the optical axis.

[0049] Assuming the incident beam after passing through a beam expander, collimator, and polarization modulator can be represented as:

[0050]

[0051] Where W(x,y) represents a rectangular window of size H×L, and AP represents the center-to-center distance between two windows. This indicates a 45° linear polarization state.

[0052] After passing through the rectangular window where the quarter-glass slide and the object are placed, the light beam can be represented as:

[0053]

[0054] Among them, A R and A O These represent the reference beam and the object beam, respectively. The Jones matrix represents a quarter-glass slide. From the above equation, it can be seen that the horizontal and vertical components of a linearly polarized beam at 45° have no phase difference, while the reference beam with circular polarization has a phase difference of π / 2.

[0055] After the Fourier transform by the first lens, the polarizing beam splitter separates the light beam into two mirror-image beams, as expressed by:

[0056]

[0057]

[0058] Step B: Interfere the reference light with linear polarization of 45° and the object light with circular polarization. After polarization modulation, the CCD camera can capture two carrier holograms with a phase shift of π / 2 at once.

[0059] Two mirror-image beams of light, after passing through a second lens and a second polarizer, form two carrier holograms with a phase shift of π / 2 on the CCD, which can be represented as:

[0060]

[0061] Step C: Recover the original light field of the target based on the two carrier holograms. Specifically, the following method can be used:

[0062] By performing a subtraction operation on the two carrier holograms obtained in step B to remove the zero-order image, it can be represented as:

[0063]

[0064] Phase recovery is then performed using a phase recovery algorithm based on the Fourier transform method, which can be expressed as:

[0065]

[0066] Where FT stands for Fourier transform, IFT stands for inverse Fourier transform, and BPF stands for bandpass filter.

[0067] To eliminate carrier frequency information and distortion information, a sample-free hologram is pre-acquired. After performing the above operations, the following can be obtained:

[0068]

[0069] Where I′ represents a hologram without a sample.

[0070] Finally, the background phase and spatial carrier can be removed by division, and the phase of the measured object can be obtained:

[0071]

Claims

1. A dual-channel polarization carrier phase shift common-path digital holographic measurement device, characterized in that, include: The system comprises a light source with wavelength λ, a collimating and expanding beam system, a first polarizer, a quarter-glass slide, a rectangular aperture, a first lens, a polarizing beam splitter, a second lens, a second polarizer, a CCD camera, and a computer. The light beam emitted from the light source, after passing through the beam expanding and collimating system, forms a planar beam. After passing through the first polarizer, it becomes linearly polarized at 45°. It then reaches the rectangular aperture. The half-beam passing through the window where the sample is placed carries object information and continues propagating in a linearly polarized state at 45°. The half-beam passing through the window where the quarter-glass slide is placed does not carry sample information and propagates in a circularly polarized state. Both beams propagate along the same path to the first lens. After passing through the polarizing beam splitter, the beam is replicated into two mirror-image beams and continues propagating along the same path to the second lens. After passing through the second polarizer, two phase-shifted carrier holograms are simultaneously acquired on the CCD camera and transmitted to the computer. The first and second lenses constitute a 4f system. The sample and the quarter-glass slide are placed in the two windows of the rectangular aperture, respectively. Both the first and second polarizers are placed perpendicular to the optical axis. The CCD camera is positioned on the back focal plane of the second lens.

2. The dual-channel polarization carrier phase shift common-path digital holographic measurement device according to claim 1, characterized in that: The polarizing beam splitter is placed at a 45° angle to the optical axis, 1-2 cm in front of the Fourier plane of the first lens.

3. A measurement method using the dual-channel polarization carrier phase shift common-path digital holographic measurement device as described in claim 1 or 2, characterized in that, include: Step A: After passing through the first polarizer, the light source reaches the rectangular aperture, forming an object beam with a 45° linear polarization state and a reference beam with a circular polarization state. The beam is then copied into two mirror-image beams by a polarizing beam splitter at a 45° angle to the optical axis. Step B: Interfere the linearly polarized reference light with 45° and the circularly polarized object light, and after polarization modulation, capture two carrier holograms with π / 2 phase shift in one go by a CCD camera; Step C: Recover the original light field of the target based on the two carrier holograms.

4. The measurement method according to claim 3, characterized in that: The two mirror-image beams described in step A satisfy the following: Where W(x,y) represents a rectangular window of H×L, AP represents the center distance between two windows, AR and AO represent the reference beam and the object beam, respectively, and φ represents the phase of the object to be measured.

5. The measurement method according to claim 3, characterized in that: The two carrier holograms with a phase shift of π / 2 described in step B satisfy the following: Where W(x,y) represents a rectangular window of H×L, AP represents the center distance between two windows, AR and AO represent the reference beam and the object beam, respectively, φ represents the phase of the object under test, and f represents the carrier magnitude.

6. The measurement method according to claim 3, characterized in that: Step C, which involves recovering the original light field of the target based on the two carrier holograms, includes: The zero-order image is removed by subtracting the two carrier holograms obtained in step B: Where AR and AO represent the reference beam and object beam, respectively, φ represents the phase of the object under test, and f represents the carrier magnitude; Then, phase recovery is performed using a phase recovery algorithm based on Fourier transform: Where FT stands for Fourier transform, IFT stands for inverse Fourier transform, and BPF stands for bandpass filter; After acquiring a hologram without a sample and performing the above operations, the following result is obtained: in, Indicates no sample hologram; Finally, the background phase and space carrier are removed by division to obtain the phase of the measured object: 。

Images