Cao Zhaoliang

Diffractive characteristics of the liquid crystal spatial light modulator

The liquid crystal spatial light modulator (LC SLM) is very suitable for wavefront correction and optical testing and can produce a wavefront with large phase change and high accuracy. The LC SLM is composed of thousands of pixels and the pixel size and shape have effects on the diffractive characteristics of the LC SLM. This paper investigates the pixel effect on the phase of the wavefront with the scalar diffractive theory. The results show that the maximum optical path difference modulation is 41 μm to produce the paraboloid wavefront with the peak to valley accuracy better than λ/10. Effects of the mismatch between the pixel and the period, and black matrix on the diffraction efficiency of the LC SLM are also analysed with the Fresnel phase lens model. The ability of the LC SLM is discussed for optical testing and wavefront correction based on the calculated results. It shows that the LC SLM can be used as a wavefront corrector and a compensator.

Improvement of Response Performance of Liquid Crystal Optical Devices by using a Low Viscosity Component

Difluorooxymethylene-bridged (CF2O) liquid crystal (LC) with low viscosity is prepared and used as a fast response LC material. When the material is mixed with isothiocyanato LCs with high birefringence, the viscoelastic coefficient of the mixture decreases evidently and, accordingly, the response performance increases. While the concentration of CF2O LCs is about 7%, the LC mixture approximately maintains high birefringence and exhibits a fastest response performance that is 14% higher than that of pure isothiocyanato LCs. Therefore, the LC material and mixing method could find useful applications in optical devices.

Simulated human eye retina adaptive optics imaging system based on a liquid crystal on silicon device

In order to obtain a clear image of the retina of model eye, an adaptive optics system used to correct the wave-front error is introduced in this paper. The spatial light modulator that we use here is a liquid crystal on a silicon device instead of a conversional deformable mirror. A paper with carbon granule is used to simulate the retina of human eye. The pupil size of the model eye is adjustable (3-7 mm). A Shack–Hartman wave-front sensor is used to detect the wave-front aberration. With this construction, a value of peak-to-valley is achieved to be 0.086 λ, where λ is wavelength. The modulation transfer functions before and after corrections are compared. And the resolution of this system after correction (691p/m) is very close to the dirraction limit resolution. The carbon granule on the white paper which has a size of 4.7 μm is seen clearly. The size of the retina cell is between 4 and 10 mu;m. So this system has an ability to image the human eyes retina.

Application of adaptive optics in biological fluorescent microscopy

Microscopy is an essential means for the Life Sciences research under the sub-micron scale. Because of the advantage in specific marking, dynamic indication, high contrast and non-destructive style, the biological fluorescence microscopy plays an important role in in-vivo imaging. When propagating in the non-transparent, non-homogeneous, anisotropic biological tissue, the excitation and emission light both will be distorted by refraction, scattering, absorption and other unknown effects and the point spread function (PSF) in each path will be consequently degraded. In order to improve the spatial resolution of fluorescence microscopy and increase the imaging depth, the adaptive optical technology has been employed in the microscope system to detect and correct the above aberrations in real-time. In this paper, aberrations in fluorescence microscope have been specified in different sources, both aberration sensing and correction methods have been introduced, and the characteristics of aberration correction in different imaging modes of fluorescence microscopy have been summarized. Then the latest applications of adaptive optics in different types of fluorescence microscopy have been discussed here and the further development trend is concluded.

The review of liquid crystal wavefront corrector with fast response property

Liquid crystal wavefront corrector (LCWFC) is an optical device that can modulate wavefront of incident light, and shows advantages of high density pixels, high reliability, and high precision accuracy, and can be used in the field of optical beam shaping, optical information processing and beam transforming. All these application model show broad application prospect of LCWFC. When LCWFC is used in the optics systems, a fast response speed is always required, such as 1 ms. In optical application, specific modulation depth is always required. If the modulation depth is 1 λ , the response time of the commercial LCWFC is slow, such as, 10 ms, which block the application of LCWFC. The response speed of LCWFC always depends on two elements, the properties of LC material and the parameters of LC device. Firstly, fast response liquid crystal material with high birefringence and low viscosity was studied and reviewed in our research group. Secondly, the optimization of LC device parameters and driving method was reviewed. By the research in LC material and device, the response time of LCWFC can be fast to sub-millisecond, which will highly enhance the application region and depth of LCWFC.

Advancement of adaptive optics in astronomical observation

Adaptive optics is used to compensate the atmospheric turbulence aberration for diffractive limit images, which makes the angular resolution of large aperture telescope not limited by the seeing or atmospheric coherence length. The continuous improvements of wavefront sensing, correctors and enlarged FOV for adaptive optics accelerate the development of astronomy. The main adaptive optics techniques include classical FOV and high resolution astronomical observation, extro-planet observation and solar observations and so on. And they have different technique requirements for adaptive optics. In the paper, we give some summarization and expectation of the advancement in the above three fields, especially in some new elemental techniques in detail, which will be helpful for our national adaptive optics development in large aperture telescopes.

High closed loop correction accuracy with a liquid crystal wavefront corrector

We investigate the accurate control of a liquid crystal wavefront corrector. First, the Gamma correction technique is adopted to amend the nonlinear phase modulation. Then, the control method and wavefront reconstruction are considered. Lastly, a closed loop correction experiment is carried out and a high correction accuracy is obtained with peak to valley (PV) of 0.08? (? = 632.8 nm), the wavefront phase rms 0.015?, as well as the Strehl ratio of 0.99. The diffraction-limited resolution is achieved.