When radially polarized light beams focus through high numerical-aperture lens, there will be a very strong longitudinal component of the light field near the focus. And, under the condition of certain system parameters, they can shape a spot which is over the focusing spot of the diffraction limit, which are the superiorities that linearly polarized light and circularly polarized light do not have. Besides, what we have found in the experiment is that radially polarized femtosecond laser pulses own the same superiorities, which provides the basis for using the focusing characteristics of radially polarized light beams under the condition of shorter and more powerful laser pulses. So far, although people have studied a lot on radially polarized light beams, this kind of light beams’ focusing characters are rarely researched. What is worse, most research of its focusing characters still stays in the stage of theoretical simulation，and it seems that none of people have really studied it by the way of experiments. This article is precisely based on this. On the basis of predecessors' a lot of theoretical research, the article pays more attention on analyzing radially polarized light beams’ focusing character through experiments. What’s more, the article, based on femtosecond laser pulses, compares the differences of the focusing nature among linearly polarized light, circularly polarized light and radially polarized light. And it gets the conclusion that radially polarized femtosecond laser pulses have better focusing character in longitudinal light field, confirming the feasibility that radially polarized light beams can be used in the fields of pulling, catching, and accelerating particles, metal cutting and high-density storage.
The crosstalk reduction of differential readout technology for Super-Resolution Near-field Structure (Super-
RENS) disc system is analyzed. We calculate the crosstalk for both differential readout technology and normal
readout technology by using scalar diffraction theory. Numerical analyses indicate that the differential readout
technique is effective as a mean of crosstalk reduction. Further analyses demonstrate the effects of different
Gaussian-weighted beams, defocus and track error on cross-talk ratio for both readout technologies. Simulations
show that the wide incident beam is preferable to gain low crosstalk. By comparing the two kinds of readout
technologies, we also find that the differential readout technology always obtains higher quality signal.
With excellent physical properties the photorefractive crystals, such as BSO (Bi<sub>12</sub>SiO<sub>20</sub>), BaTiO<sub>3</sub> and GaAs materials, have, can be widely used in optical correlator to implement auto pattern recognition. As the basic devices in optical
correlator, the properties of optically-addressed spatial light modulator are very important. By analyzing the dynamic
process of the BSO spatial light modulator, especially the changes of the read-out light while in writing under various
operation modes, the distinctness between various operation modes is summarize. Furthermore, considered with the
photo-induced current pulses, the method to optimize the BSO spatial light modulator is proposed. The BSO spatial light
modulator working in optimum operation mode is used to design a optical correlator to implement auto pattern
Along with the development of parallel optical computing, more and more two-dimensional optical modulating and
transforming devices with high response speed are needed. As the response times of most of the photorefractive crystals
are very short, optically addressed photorefractive BSO spatial light modulators are the most important devices which
have been successfully used in many two-dimensional optical information processing systems. However, the response
time is still too large for optical computing applications. In order to achieve adequate contrast ratio, a majority of the
operation process of the photorefractive spatial light modulators have to account for the accumulating of the
photoinduced charges so as to build up a strong internal electric field. The experiment results show that, the
photoinduced currents through the external circuits which provide the applied voltage behave with the characteristics of
pulses. The properties of the current pulses vary with the wavelength of the write-light, the direction of the external field,
the value of the applied voltage, the thickness of the BSO films and the properties of the external circuits. The analysis of
the photoinduced current pulses is useful for optimizing the structure, the operation modes and the performance of the
photorefractive spatial light modulators. Furthermore, the analysis can provide some useful information for choosing
appropriate materials and devices for optical computing applications, and building up efficient all-optical architecture for
the future parallel optical computers.
The applications of the joint transform correlator are partly limited by the information loss of the power spectra while
being detected and transmitted by conventional detectors and electrically addressed spatial light modulators. The
re-writable diarylethene films, which used to be mainly used in optical storage, are successfully tried to detect and
transmit the power spectra of the joint transform correlator instead of the CCDs and the electrically addressed spatial
light modulators. According to the experiment results and the corresponding comparisons and discussions, the
re-writable diarylethene films can be used to detect and transmit the power spectra of the joint transform correlator
better than the CCDs and the electrically addressed spatial light modulators in the case of decreasing the information
loss. With high resolution and large dynamic range, besides optical storage, the re-writable diarylethene films will be
widely used in optically addressed spatial light modulators if the operation period can be shortened remarkably.
Optical digital processor is the core of some future optical parallel computing systems. A novel optical discrete
correlation processor using a high-speed digital micromirror device is proposed, which mainly consists of a VanderLugt
correlator. In the processor, the computer generated hologram filters which are inputted by the digital micromirror device
will determine the specific logical operations. With properties of high reflectivity, high resolution and short response
time, the digital micromirror device can control the wave-front of the light beams with high optical efficiency, large
contrast ratio and high rate. An experimental prototype is constructed to demonstrate some specific logical operations.
The experiment results indicate that, the novel optical digital processor based on digital micromirror device can perform
some specific logical operations properly, and the digital micromirror device can remarkably improve the performance of
the optical digital processor.
Some damages may occur when sensitive BSO (Bi<sub>12</sub>SiO<sub>20</sub>) asymmetric spatial light modulators operate in some given
modes, even though the power of the writing light beam is far less than the optical damage threshold. According to some
experimental results and corresponding analysis, high voltage and given operating modes may lead to too high intensity
photocurrent pulse in short time, consequently large quantity of heat in ultra-small area may make the narrow areas swell
up and thus the damage of the BSO film. In order to get well sensibility, well resolution and well response speed without
damages of the spatial light modulators, optimizing the structure parameters and the operating modes is necessary.