Mueller-matrix microscope and measurement and calibration methods using the same

• US 10,345,568 B2
• Filed: 04/13/2017
• Issued: 07/09/2019
• Est. Priority Date: 12/12/2016
• Status: Active Grant

• Current Assignee: Wuhan Eoptics Technology Co. Ltd. (Shanghai Precision Measurement Semiconductor Technology, Inc.)
• Original Assignee: Wuhan Eoptics Technology Co. Ltd. (Shanghai Precision Measurement Semiconductor Technology, Inc.)
• Inventors: Chen, Xiuguo, Chen, Jun, Chen, Chao, Liu, Shiyuan
• Primary Examiner(s): Elahi, Shan E
• Application Number:
  US15/487,407
• Publication Number:
  US 20180164566A1
• Time in Patent Office: 817 Days
• Field of Search: 348 79
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 2201/0683 Brewster plate; polarisation controlling elements
• CPC Class Codes: G02B 21/0092 Polarisation microscopes
• CPC Class Codes: G02B 21/361 Optical details, e.g. image relay to the camera or image sensor G02B21/364 takes precedence; illumination details G02B21/06 and subgroups
• CPC Class Codes: G02B 21/367 providing an output produced by processing a plurality of individual source images, e.g. image tiling, montage, composite images, depth sectioning, image comparison
• CPC Class Codes: G02B 26/0816 by means of one or more reflecting elements
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/42 Coupling light guides with opto-electronic elements
• CPC Class Codes: G02F 1/0027 Ferro-electric materials
• CPC Class Codes: G02F 1/0045 Liquid crystals characterised by their physical properties

Abstract

A Mueller-matrix microscope, including: a polarizing unit and an analyzing unit. The polarizing unit is configured to modulate a light beam emitted from an external light source module to yield a polarized light beam, and then to project the polarized light beam on the surface of a sample to be measured. The analyzing unit is configured to analyze the polarization state of a light beam reflected from the surface of the sample, to acquire information of the sample. The analyzing unit includes a polarization state analyzer (PSA) and a backside reflection suppression (BRS) unit. The PSA unit is configured to demodulate the polarization state of the light beam; and the BRS unit is configured to suppress the backside reflections from transparent substrate.

Claims

1. A Mueller-matrix microscope, comprising:

an external light source module, the external source module comprising a light source, a wavelength selector, an optical fiber coupler, and an output optical fiber;

a polarizing unit, the polarizing unit comprising a first lens, an aperture diaphragm, a plane mirror, a polarization state generator (PSG), a beam splitter, a second lens, and an objective lens, and the PSG comprising a polarizer, a first ferroelectric liquid crystal device, a first quarter-wave plate, and a second ferroelectric liquid crystal device;

an analyzing unit, the analyzing unit comprising a polarization state analyzer (PSA) and a backside reflection suppression (BRS) unit, the PSA comprising a third ferroelectric liquid crystal device, a second quarter-wave plate, a fourth ferroelectric liquid crystal device, and an analyzer, and the BRS unit comprises a third lens, a pinhole, and a fourth lens;

a controller;

a computer;

a sample stage; and

a camera;

wherein

the external source module, the wave selector, and the optical fiber coupler are connected in sequence through optical fibers;

the optical fiber coupler is connected to the output optical fiber;

an output end of the output optical fiber, the first lens, the aperture diaphragm, the plane mirror, the polarizer, the first ferroelectric liquid crystal device, the first quarter-wave plate, the second ferroelectric liquid crystal device, the beam splitter, the second lens, the objective lens, and the sample stage are disposed in order to form an optical path;

the second lens is disposed at a frontside of the beam splitter;

the polarizer, the first ferroelectric liquid crystal device, the first quarter-wave plate, and the second ferroelectric liquid crystal device are disposed coaxially along the optical path;

the PSA is aligned with the BRS unit;

the PSA and the BRS unit are dispose at a backside of the beam splitter;

the third ferroelectric liquid crystal device, the second quarter-wave plate, the fourth ferroelectric liquid crystal device, the analyzer, the third lens, the pinhole, and the fourth lens are aligned in that order at the backside of the beam splitter;

the first ferroelectric liquid crystal device and the second ferroelectric liquid crystal device are connected to the controller;

the third ferroelectric liquid crystal device and the fourth ferroelectric liquid crystal device are connected to the controller;

the controller and the camera are connected to the computer; and

the camera is disposed at a back focal plane of the fourth lens;

when in use,

the polarizing unit modulates a light beam emitted from the external light source module to yield a polarized light beam, and then projects the polarized light beam on a surface of a sample disposed on the sample support to be measured; and

the analyzing unit analyzes the polarized light beam reflected from the surface of the sample and acquires information of the sample.

2. The microscope of claim 1, wherein when in use,

the light beam emitted from the external light source module is collimated by the first lens to yield a collimated light beam;

the collimated light beam is allowed to pass through the aperture diaphragm, and is specularly reflected by the plane mirror;

the reflected light beam enters the polarization generation unit and is modulated to yield the polarized light beam; and

the polarized light beam is allowed to pass through the beam splitter, the second lens, and the objective lens, in that order, and then is projected on the surface of the sample.

3. The microscope of claim 2, wherein the plane mirror is disposed on a rotating table.

4. The microscope of claim 2, wherein the beam splitter is configured to reflect the light beam in the polarizing unit to change a direction of propagation of the light beam, meanwhile, the beam splitter is configured to allow the light beam to penetrate through in the analyzing unit;

and the beam splitter is a non-polarization beam splitter.

5. The microscope of claim 2, wherein when in use, the light beam reflected from the surface of the sample is collected by the objective lens, and passes through the second lens, the beam splitter, the PSA unit, and the BRS unit, in that order, and then enters the camera;

the PSA unit is configured to demodulate the polarization state of the light beam; and

the BRS unit is configured to suppress the backside reflections from transparent substrate.

6. The microscope of claim 5, wherein focal lengths of the third lens and the fourth lens are conjugate;

the pinhole is disposed at a conjugate focus of the third lens and the fourth lens.

7. The microscope of claim 1, wherein the light beam generated by the light source is selected by the wavelength selector to yield a single-wavelength light beam;

the single-wavelength light beam is transmitted to the output optical fiber via the optical fiber coupler; and

the output optical fiber is used as an output end of the external light source module.

8. A method for measuring a sample using the microscope of claim 1, the method comprising:

1) placing the sample at the sample stage;

regulating the polarizing unit and the analyzing unit to obtain an image of an area of the sample at the camera;

2) collimating a single-wavelength light beam emitted from the external light source module to yield a collimated light beam;

modulating the collimated light beam using the PSG to yield elliptically polarized light; and

projecting the polarized light on the surface of the sample;

3) demodulating the light beam reflected from the surface of the sample using the PSA; and

allowing the light beam to enter the camera to obtain different intensity signals of the light beam under different polarization states;

4) calculating measured Mueller-matrix data of the sample at each pixel on the camera according to the intensity signals in

     3), all the measured Mueller-matrix data at each pixel form measured Mueller-matrix data of the sample in an entire field of view (FOV);

5) changing a wavelength λ and

an angle of incidence θ

of the light beam;

rotating the sample stage and altering an azimuth angle ϕ

between the light beam and the sample;

repeating

     2)-4), and calculating the measured Mueller-matrix data under different wavelengths λ

, different angles of incidence θ

, and different azimuth angles ϕ

;

6) calculating theoretical Mueller-matrix data of the sample according to a Fresnel formula based on a given configuration of the wavelength λ

, the angle of incidence θ

, and the azimuth angle ϕ

; and

7) fitting the measured Mueller-matrix data to obtain actual Mueller-matrix data of the sample;

comparing the actual Mueller-matrix data with the theoretical Mueller-matrix data;

when a deviation between the actual Mueller-matrix data and the theoretical Mueller-matrix data falls within a given range, confirming the actual Mueller-matrix data is accurate;

calculating parameter values of the sample at each pixel according to the actual Mueller-matrix data;

calculating parameter values of the sample at all pixels to obtain a three-dimensional microstructure of the sample in the entire FOV;

when the deviation is out of the given range, repeating

     2)-6) until the deviation between the actual Mueller-matrix data and the theoretical Mueller-matrix data falls within the given range, obtaining the three-dimensional microstructure of the sample.

9. An in situ calibration method of a beam splitter and an objective lens using the microscope of claim 1, the method comprising:

1) calibrating a Muller matrix of the beam splitter when the beam splitter is configured to allow a light beam to penetrate through and reflect the light beam; and

2) calibrating a Muller matrix of the objective lens when the objective lens is configured to illuminate in an incident light path unit and collect a reflected light beam.