Up to now, a variety of methods have been developed for the single-shot THz detection, which include spectral encoding
technique [2-3], optical streak camera , non-collinear geometry spatial encoding , non-collinear cross correlation
technique , retrieval algorithm based on in-line spectral interferometry , two-dimensional electro-optic imaging
with dual echelons , tilted front collinear geometry , etc.
For a single-shot characterization of THz pulse, all of the schemes mentioned above can be, however, only employed to
measure the electric field of a single-shot THz either in its spatial or temporal domain, respectively, in real time.
In this paper, we describe a method for a single-shot recording of the full spatiotemporal electric field, E(x, y, t), of
freely propagating terahertz pulse based on the electro-optic (E-O) sampling technique and the pulsed digital holographic
approach. From a series of sub-holograms recorded digitally, the complete THz electric field E(x, y, t) can be recovered
by the following digital reconstruction algorithm. The spatial and temporal resolutions are limited by the wavelength of
terahertz pulse and the probe pulse duration, respectively. Our new method will open a possibility of a full
characterization of the three-dimensional THz field E(x, y, t) in a single-shot mode.
Shadowgraphs of dynamic processes outside and inside the target during the intense femtosecond laser ablation of silica
glass at different energy fluences are recorded. Two material ejections outside the target and two corresponding stress
waves inside the target are observed. In particular, a third stress wave can be observed at energy fluence as high as 40
J/cm2. The pressure, the temperature, the free electron density, and the ionic components at the laser pulse end are
estimated, based on which the mechanical reaction of the laser heated material is investigated. According to our analysis,
the first wave is a thermoelastic wave, while the second and the third may be generated subsequently by the mechanical
expansions. Besides, the velocities of the stress waves are deduced from the time-resolved shadowgraphs, and it is found
that the first stress wave propagates with a velocity greater than the sound velocity, while the second stress wave
propagates with a velocity less than the sound velocity. Therefore, the first wave is a supersonic shockwave with a high
stress magnitude, while the second may be the plastic stress wave or subsonic shockwave with a lower stress magnitude.
Further more, the temporal evolution the second stress wave is investigated, and its velocity is found to increases
gradually at large delay times. According to the extrapolation curve, however, it is speculated that the velocity decreases
from a high value initially, which could be due to the interaction between the first and second stress waves at small delay
times. These results can provide a further support to the theory of highpressure shock phenomena in femtosecond laser
We report on approaches of pulsed digital holographic recording and its relevant digital reconstruction based on Fourier
optics for measurements of high resolution in time domain or in space domain, in which angular division multiplexing
system is respectively employed to record multiple images in a single frame of a CCD. This new approach can be used to
record either a series of images in an ultra-fast process with high resolution in time domain, or to record a transparent
object with super-resolution in space domain. In the digital reconstruction process, Fourier transformation and frequency
filtering in the Fourier plane will be employed to separate the spatial spectra of the multiple recordings, and each of the
reconstructed images can be displayed individually with a time resolution of the femto-second order or fused into an
image of the object with a synthetic aperture.
We report on pulsed digital micro holographic systems recording ultra-fast process of the femto-second order, by
spatially angular division multiplexing (SADM) and wavelength division multiplexing (WDM), respectively. Both
intensity and phase images of the digitally reconstructed images are obtained through Fourier transformation and digital
filtering, which show clearly the plasma forming and propagating dynamic process of laser induced ionization of
ambient air at the wavelength of 800 nm, with a time resolution of 50 fs and frame intervals of 300 to 550 fs.
In this paper, we report, for the first time, a specially designed optical gating system of spatially angular multiplexing for ultra-short pulsed digital holography, which can be employed to record ultra-fast processes of the order of femto-second. The sampling resolution of the dynamic process ranges from 50 fs to 10 ps. By adjusting the time delays and the angles included between the sub-pulses, the system sampling interval ranging from 67 fs to 170 ps is obtained.
The beam emitted by a laser diode chip is elliptical and astigmatic. Various methods have been proposed and applied to remove the astigmatism and to produce a circular Gaussian beam. In this paper we will further propose the use of the laser diode beam correction optics in an external cavity laser. The light produced by the external cavity laser is not only circular, Gaussian, and non-astigmatic, but its coherence length is also significantly enhanced.
The laser induced ionization of ambient air is studied experimentally with laser pulses whose durations range from 50 fs up to 10 ps at 800 nm. It is found that the minimum pulse energy for detectable air ionization follows the scaling law of εth varies direct as tpx, with 0.23 < x < 0.5, and x tends to rise for longer pulses within the range of 50 fs - 500 fs. For laser pulses from 0.7 ps to 10 ps, however, x is approximately equal to 0.8. The dependence of the critical intensity for air ionization on the beam spot size is also examined with a variety of focused laser beam spot sizes in the experiments.
The use of laser diode in joint transform correlator (JTC) is discussed as an example of potential applications to optical signal processing. Effects of the coherence and astigmatism of laser diode beam are analyzed. Two methods for correcting laser diode beam using a cylindrical lens or a pair of cylindrical lenses are also reviewed. A corrected laser diode can be used in JTC to totally eliminate the effect of astigmatism.
The use of a laser diode in a joint transform correlator (JTC) is proposed. Effects of temporal coherence, spatial coherence, astigmatism, and elliptical beams are analyzed. Laser diodes can be used in JTC, and also can be used for the correlation process in a Vander Lugt correlator and reading a hologram. Even a light-emitting diode (LED) may be used for the purposes mentioned, if its exit facet is sufficiently small. Two methods for correcting a laser diode beam using a cylindrical lens or a pair of cylindrical lenses are also reviewed. A corrected laser diode can be used in JTC to totally eliminate the effect of astigmatism.
We report for the first time an application of fuzzy relations in fuzzy set theory to the color image retrieval. In the process, a new method of spatial partition of color space is developed for the comparisons. Our theoretical and experimental results show clearly the advantages of our approach in both accuracy and speed of the retrieval.
Proc. SPIE. 4922, Color Science and Imaging Technologies
KEYWORDS: Content based image retrieval, Image processing, Imaging technologies, Colorimetry, Information technology, Image retrieval, Information science, Fuzzy logic, 3D image processing, Internet technology
In this paper, we report a novel method of fuzzy color-image retrieval based on color histogram correlation, for which peaks of the histograms are first ranked according to their heights and then the correlation based on both height and position will be calculated for correspondent rank respectively. A correlation result will be defined by ?- cut procedures. Experiment results confirmed the effectiveness of the method.
We review the fundamental development in the last decade of white-light optical information processing for digital color photography and its instrumentation for the applications to education in white-light optical information processing. Applications to education in white-light information processing for graduated students majoring in physics, optics, information science, or opto-electronics will be introduced with emphasis.
We present theoretical analysis and experimental results of a white light JTC (joint transform correlator) using a tri- color grating to encode color patterns. The power spectra of the encoded pattern are easy for parallel channeling, and the zero order power spectrum also forms an important channel for the shape-only correlation.
We report a new experimental solution for implementing joint transform correlator (JTC) by subtracting modified Fourier spectrum described in , in which the authors used an additional contrast-reversed reference to enhance the expected correlation peaks for binary image processing. In our new solution, there is only a phase difference between the two reference images, and the amplitude of them, however, remain the same. Besides, our solution is generally available for the optical processing with binary images as well as with images of multiple gray levels.
We present the theoretical analysis and the experimental proposal of a one-step method for implementing a large scale (50 X 50 approximately 100 X 100) holographic array illuminator with high diffraction efficiency and low aberration due to the wavelength difference between recording and reconstruction.
We demonstrate and characterize the use of an optically addressed ferroelectric liquid crystal (FLC) spatial light modulator (SLM) as a spatial filter. The photosensor associated with the liquid crystal is a PIN photodiode made of hydrogenated amorphous silicon (a-Si:H). Both the amplitude and the phase of the reflection coefficient are observed to be modulated by the write beam. The filter function can be reconfigured at a submillisecond rate with incoherent illumination.
We present a holographic array illuminator based on the Talbot effect. This illuminator can be used in massively parallel architecture with a good efficiency and minimal aberrations in the reconstruction at a different wavelength.
We report, for the first time, a simple method using an array of logic XNOR gates to
execute the optical process of vector-matrix multiplication or inner-product correlation, where
the two levels of light intensity -on and off- can be used to represent bipolar binary vectors.
Optical implementation of neural networks based on the Hopfield model is described as an
example to show the application of this novel method.
We present optical bistability in silicon on sapphire (SOS) thermooptical SEED structures at a visible wavelength of A = 514nm. Theoretical analysis and experimental results show that bistability is due to increasing absorption and thermally induced change of the internal resistance.