Polarization Imaging Camera Research Articles

High-speed phase-shifting incoherent digital holography (invited)

We propose high-speed incoherent digital holography with a recording speed of 1,000 fps, which is designed for the three-dimensional (3D) motion-picture measurement of moving objects with high temporal resolution. We adopt single-shot phase-shifting incoherent digital holography, a high-speed polarization-imaging camera system, and a palm-sized self-interference interferometer designed for spatially and temporally incoherent light, to implement a high-speed phase-shifting incoherent digital holography system. High-speed four-dimensional (4D) (3D and time) measurement capability is experimentally demonstrated, using the constructed incoherent digital holography system set on a wagon and a daily-use white-color light-emitting diode.

Motion-Picture Recording of Light Pulses With Ultrashort Time Difference by Polarization Camera

Ultrafast optical imaging techniques for light propagation are useful in many fields, such as physics, chemistry, and biomedicine. In this letter, we propose an imaging technique for obtaining dual motion pictures of propagating light pulses with an ultrashort time difference. To realize the proposed technique, we employed a polarization imaging camera to record dual motion pictures of propagating light pulses without superposition. We also constructed and introduced an optical delay setup for generating light pulses with ultrashort time differences. In addition, the capturing of two propagating light pulses with ultrashort time differences given by the optical delay setup was experimentally demonstrated. Specifically, we recorded the first and second light propagations for 302 fs with an 890 fs time difference.

Single-path single-shot phase-shifting digital holographic microscopy without a laser light source.

We propose single-path single-shot phase-shifting digital holographic microscopy (SSP-DHM) in which the quantitative phase information of an object wave is acquired without a laser light source. Multiple phase-shifted holograms are simultaneously obtained using a linear polarizer, a liquid crystal on a silicon spatial light modulator (LCoS-SLM), and a polarization-imaging camera. Complex amplitude imaging of a USAF1951 test target and phase imaging of transparent HeLa cells are performed to show its quantitative phase-imaging ability. We also conduct an experiment for the motion-picture imaging of transparent particles to highlight the single-shot imaging ability of SSP-DHM.

Recordable-Time Extension of Digital Light-in-Flight Recording by Holography Using a Polarization-Imaging Camera

Digital light-in-flight recording by holography is a powerful tool for observing ultrashort light pulse propagation as a motion picture. However, the recordable time of the technique has been limited by the lateral length of the image sensor used for the recording of the hologram, and no technique for extending the recordable time has been reported yet. Then, to extend the recordable time of digital light-in-flight recording by holography, we proposed a technique that records two holograms as a single hologram using double reference light pulses with an image sensor. In this technique, the image sensor is spatially divided into multiple micro-areas. Each micro-area consists of 2 × 1 pixels and records 1 pixel of each of the two holograms. We employed a polarization-imaging camera in order to implement the proposed technique to extend the recordable time. This technique is a new application of the polarization-imaging camera. We experimentally succeeded in extending the recordable time for the first time using the proposed technique. Specifically, we recorded the motion picture of the ultrashort light pulse propagation for 1.04 ps.

Imaging Polarimetry of the 2017 Solar Eclipse with the RIT Polarization Imaging Camera

Micropolarizer-based sensors are dramatically smaller and more mechanically robust than other polarimeters with similar spectral response and snapshot capability. To determine the suitability of these new polarimeters for astronomical applications, we developed the RIT Polarization Imaging Camera to investigate the performance of these devices, with a special attention to the low signal-to-noise regime. We found that, using the current calibration, RITPIC is capable of detecting polarization signals as small as ∼0.3%. To demonstrate the stability of RITPIC’s calibration and its extreme portability, we performed imaging polarimetry of the Solar corona in Madras, Oregon during the total Solar eclipse of 2017. The maximum polarization we measured was ∼47% in the blue and red color channels, which agrees well with the maximum value predicted for a Thomson scattering corona. Similarly, we found no strong deviations in the angle of linear polarization from the tangential direction. The relative ease of data collection, calibration, and analysis provided by these sensors suggest than they may become an important tool for a number of astronomical targets.

分振幅偏振成像相机标定方法研究

分振幅偏振成像相机标定方法研究

Single-shot Fresnel incoherent digital holography based on geometric phase lens

ABSTRACTSingle-shot and incoherent imaging are two important properties of digital holography that can extend its application range. In this study, a simple, compact, in-line Fresnel incoherent digital holographic recording system is proposed that is capable of single-shot and three-dimensional imaging. A geometric phase lens is used as the common-path beam splitter based on its special wave separation property. Parallel phase-shifting holography is used to achieve single-shot operation with the use of a polarization imaging camera together with space-division multiplexing. The capabilities of the proposed technique are experimentally confirmed by imaging two standard test charts based on a compact setup.

Astronomical Polarimetry with the RIT Polarization Imaging Camera

In the last decade, imaging polarimeters based on micropolarizer arrays have been developed for use in terrestrial remote sensing and metrology applications. Micropolarizer-based sensors are dramatically smaller and more mechanically robust than other polarimeters with similar spectral response and snapshot capability. To determine the suitability of these new polarimeters for astronomical applications, we developed the RIT Polarization Imaging Camera to investigate the performance of these devices, with a special attention to the low signal-to-noise regime. We characterized the device performance in the lab, by determining the relative throughput, efficiency, and orientation of every pixel, as a function of wavelength. Using the resulting pixel response model, we developed demodulation procedures for aperture photometry and imaging polarimetry observing modes. We found that, using the current calibration, RITPIC is capable of detecting polarization signals as small as ∼0.3%. The relative ease of data collection, calibration, and analysis provided by these sensors suggest than they may become an important tool for a number of astronomical targets.

Polarization imaging camera with a waveplate array fabricated with a femtosecond laser inside silica glass.

In this study, we demonstrate a polarization imaging camera with a waveplate array of a silica glass fabricated by femtosecond (fs) laser direct writing. To use a waveplate array of silica glass for polarization imaging, non-uniformity of the transmittance and retardance in the waveplates must be considered. Therefore, we used a general method of polarization analysis with system matrices determined experimentally for all the units in the waveplate array. We found that a figure of merit based on the determinant of the system matrix could be applied to improve the accuracy of analysis and the robustness to the retardance dispersion for both the simulated and the fabricated waveplate array.

Three-dimensional motion-picture imaging of dynamic object by parallel-phase-shifting digital holographic microscopy using an inverted magnification optical system

We constructed a parallel-phase-shifting digital holographic microscopy (PPSDHM) system using an inverted magnification optical system, and succeeded in three-dimensional (3D) motion-picture imaging for 3D displacement of a microscopic object. In the PPSDHM system, the inverted and afocal magnification optical system consisted of a microscope objective (16.56 mm focal length and 0.25 numerical aperture) and a convex lens (300 mm focal length and 82 mm aperture diameter). A polarization-imaging camera was used to record multiple phase-shifted holograms with a single-shot exposure. We recorded an alum crystal, sinking down in aqueous solution of alum, by the constructed PPSDHM system at 60 frames/s for about 20 s and reconstructed high-quality 3D motion-picture image of the crystal. Then, we calculated amounts of displacement of the crystal from the amounts in the focus plane and the magnifications of the magnification optical system, and obtained the 3D trajectory of the crystal by that amounts.

An apparatus for birefringence and extinction angle distributions measurements in cone and plate geometry by polarization imaging method

A new apparatus for flow visualization based on Polarization Imaging Method (PIM) is developed. In this method, the polarization imaging camera, which is composed of a photonic crystal and CCD image sensor, is used to measure anisotropy of refractive index tensor. The photonic crystal placed in the front of CCD image sensor works as an assembly of analyzer plates for each of photo detectors of the image sensor, which provides four polarization components of image. By analysis of the polarization imaging data, the spatial distribution of birefringence and extinction angle can be obtained simultaneously. Since birefringence and extinction angle have strong relationship with stress and orientation angle due to Stress-Optical Rule (SOR), their distribution is appropriate to understand non-uniform flow. The advantage of the apparatus was examined by imaging flow of wormlike micellar solution in uniform and non-uniform shear flows. In the uniform shear rate geometry of cone and plate, we successfully obtained spatial distribution of birefringence and extinction angle of flow-induced structure of threadlike micelles.

Damage Detection in Transparent Materials Using Non-Contact Laser Excitation by Nano-Second Laser Ablation and High-Speed Polarization-imaging Camera

Although transparent materials with birefringent properties (e.g., solar panels and separator films for secondary cells) are common, damage detection during the manufacturing process is crucial to economically realize high-quality materials. Herein a method using a pulsed-laser and a high-speed polarization-imaging camera is proposed to rapidly detect damage, including scratches and dents, in transparent materials. Specifically, as stress waves, which are generated by a non-contact impulse excitation from laser ablation, propagate through a material, the stress concentrations induced around damage are measured as the two-dimensional birefringent phase differences using a high-speed polarization-imaging camera with a microsecond-order temporal resolution. When stress is dominant, the distribution of the measured birefringent phase difference can be considered the relative distribution of stress. Using acrylic plates as a representative transparent material with several hundred micrometers of damage (e.g., a dent or a scratch), we demonstrate that the proposed method detects damage in a very short timeframe of several microseconds.

Polarization imaging over sea surface - a method for measurements of Stokes components angular distribution

This article describes a method for determining the angular distribution of light polarization over a roughened surface of the sea. Our method relies on measurements of the Stokes vector elements using a polarization imaging camera that operates using the Division of Focal Plane (DoFP) method. It uses special monochrome CCD array in which the neighbouring cells, instead of recording different colours (red green and blue), are equipped with micropolarizers of four directions (0, 45, 90 and 135 degrees). We combined the camera with a fish-eye lens of Field of View (FoV) > 180 deg. Such a large FoV allowed us to crop out the fragment of the frame along the circular horizon, showing a view covering all directions of the hemisphere. Because of complicated optical design of the fish-eye lens (light refraction on surfaces of parts of the lens) connected to the sensor we checked the accuracy of the measurement system. A method to determine the accuracy of measured polarization is based on comparison of the experimentally obtained rotation matrix with its theoretical form. Such a comparison showed that the maximum error of Stokes vector elements depended on zenith angle and reached as much as 24% for light coming from just above the horizon, but decreased rapidly with decreasing zenith angle to the value of 12% for the angles 10° off the edge of FoV. Moreover we present the preliminary results prepared over rough sea surface. These results include total intensity of light, Degree of Linear Polarization (DoLP) and their standard deviations. The results have been averaged over one thousand frames of a movie. These results indicate that the maximum polarization is observed near the reflection of the sun, and the signal coming from below the surface may be observed at zenith angles far from the vertical direction.

Space-bandwidth extension in parallel phase-shifting digital holography using a four-channel polarization-imaging camera

We propose a method for extending the space bandwidth (SBW) available for recording an object wave in parallel phase-shifting digital holography using a four-channel polarization-imaging camera. A linear spatial carrier of the reference wave is introduced to an optical setup of parallel four-step phase-shifting interferometry using a commercially available polarization-imaging camera that has four polarization-detection channels. Then a hologram required for parallel two-step phase shifting, which is a technique capable of recording the widest SBW in parallel phase shifting, can be obtained. The effectiveness of the proposed method was numerically and experimentally verified.

Parallel phase-shifting dual-illumination phase unwrapping

We propose a single-shot phase unwrapping technique using a single wavelength and parallel phase-shifting interferometry. In the proposed technique, an object is illuminated by two laser beams, which are emitted from the same laser, and have different illumination angles and polarizations. Two types of object waves generated by the two beams are separately and simultaneously recorded by a polarization-imaging camera. In the path of the reference wave, an array of phase retarders is placed to implement the parallel phase-shifting technique. A highly accurate three-dimensional shape is reconstructed from a single hologram. We numerically simulated the proposed technique and conducted a preliminary experiment to verify its effectiveness. It was confirmed that millimeter-order height, which was several thousand times the wavelength of the laser, can be reconstructed by the proposed technique without wrapping.

Single-shot dual-illumination phase unwrapping using a single wavelength

We propose a single-shot phase unwrapping technique using a single wavelength. In the proposed technique, an object is illuminated by two laser beams, which are emitted from the same laser, whose illumination angles and polarizations are different. Then two types of the object waves generated by the two beams are separately and simultaneously recorded by a polarization imaging camera. We conducted an experiment and a 2.5mm height object, which was 9400 times height of the wavelength of the laser, was reconstructed without wrapping.

Three-dimensional displacement measurement for diffuse object using phase-shifting digital holography with polarization imaging camera

The amount of displacement of a diffused object can be measured using phase-shifting digital holography with a polarization imaging camera. Four digital holograms in quadrature are extracted from the polarization imaging camera and used to calculate the phase hologram. Two Fourier transforms of the phase holograms are calculated before and after the displacement of the object. A phase slope is subsequently obtained from the phase distribution of division between the two Fourier transforms. The slope of the phase distribution is proportional to the lateral displacement of the object. The sensitivity is less than one pixel size in the lateral direction of the movement. The longitudinal component of the displacement can be also measured separately from the intercept on the phase axis along the phase distribution of the division between two Fourier transforms of the phase holograms.

Quadrature phase-shifting interferometer with a polarization imaging camera

We present a new high-speed phase distribution measurement, in which a polarization imaging camera is applied to a quadrature phase-shifting interferometer. The polarization imaging camera composed of a polarizer-mask on a detector array can provide simultaneously two phase-shifted data in quadrature. Two sets of two phase-shifted data in quadrature are obtained before and after a change of the interferometer such as object displacement or environmental disturbances. Phase sum and difference distributions of the interferograms between two states with arbitrary phase-shift in the interferometer are calculated with the two sets of two phase-shifted data in quadrature. This phase calculation method in the pixel displaced phase-shift method has such advantage that phase-shifted data required for the calculation of phase distributions can be obtained by only two pixels in the polarizer-mask detector array, which means no reduction of the image resolution in the other direction. The principle of this technique and experimental results are presented.

401 サブ波長格子を用いた微小波長板アレイによる偏光画像計測(GS-16 精密計測・精密加工)

401 サブ波長格子を用いた微小波長板アレイによる偏光画像計測(GS-16 精密計測・精密加工)