Active Pulse Compression Research Articles

Low Power Demonstration of a W-band Active Pulse Compressor for High Power Millimeter Waves

Low Power Demonstration of a W-band Active Pulse Compressor for High Power Millimeter Waves

Defect detection capabilities of independent component analysis for Barker coded thermal wave imaging

Active pulse compression favourable infrared imaging techniques are promising evaluation techniques among other thermal non-destructive testing and evaluation modalities for identification of subsurface defects in the test samples. This is due to their merits such as high defect detection sensitivity and resolution by using relatively low peak power heat sources and in a moderate experimentation time in comparison with widely used pulse and modulated conventional thermal wave imaging modalities. Various data processing methods have been developed to extract the thermal features of defects from the captured thermographic data. The cross-correlation based pulse compression method is recommended for Barker coded thermal wave imaging technique as it enhances the concentration of applied thermal energy into mainlobe and distributes the significantly less energy into the sidelobes of cross correlation data. In this paper, the stated property of Barker coded thermal wave imaging along with the independent component analysis approach has been utilised. The study in this paper is focused on the application of independent component analysis approach on captured thermal response data, entire cross correlation data and only the mainlobe of CC data. The results obtained clearly indicate that the application of independent component analysis on cross correlation data has improved the detectability, visibility, and contrast (interms of signal-to-noise values) of the defects. Further, the results obtained with the different methods have been compared by taking Signal to noise ratio as the figure of merit.

Application of combinations of axisymmetric modes in electrodynamic systems of high-power microwave devices

We consider some applications of combinations of axisymmetric magnetic waves of circular waveguides in microwave transmission lines, passive and active pulse compressors, delay lines, electron gyrodevices and other microwave components on the basis of analysis of the properties of such waves.

Active RF pulse compression using an electrically controlled semiconductor switch

First we review the theory of active pulse compression systems using resonant delay lines. Then we describe the design of an electrically controlled semiconductor active switch. The switch comprises an active window and an overmoded waveguide three-port network. The active window is based on a four-inch silicon wafer which has 960 PIN diodes. These are spatially combined in an overmoded waveguide. We describe the philosophy and design methodology for the three-port network and the active window. We then present the results of using this device to compress 11.4 GHz RF signals with high compression ratios. We show how the system can be used with amplifier-like sources, in which one can change the phase of the source by manipulating the input to the source. We also show how the active switch can be used to compress a pulse from an oscillator-like source, which is not possible with passive pulse compression systems.

Generation of 98 fs optical pulses directly from an erbium-doped fibre ring laser at 1.57 μm

Optical pulses as short as 98 fs at 1.57 μm have been successfully generated for the first time directly from a laserdiode pumped erbium-doped fibre laser with a nonlinear amplifying loop mirror. By using a low GVD polarisation sensitive isolator and reducing the fibre length in a nonlinear loop, 124 fs pulses were obtained. They were further shortened to 98 fs by installing an EDFA as an active pulse compressor and a positive GVD fibre for chirp compensation.

Pulse compression in a free electron laser amplifier

We have studied both theoretically and experimentally a new scheme of active pulse compression in a free electron laser (FEL) amplifier. The pulse compression scheme presented here is the following. A frequency-chirped pulse is injected into the FEL interaction region. Because of the high gain and narrow bandwidth of the FEL interaction, only the resonant frequency band of the pulse is actively amplified, resulting in a short pulse of high power coherent radiation at the output of the laser. For our experimental parameters (beam voltage ∼ 150 kV, current ∼ 5.0 A, wiggler period ⋍ 3.5 cm and gain ∼ 10 dB), pulses of a few nanoseconds were generated at ⋍ 10 GHz after an interaction length of 2.30 m, in good agreement with theoretical expectations. For the same input pulses (width > 100 ns, frequency chirp α2π ∼ 5 MHz/ns), the obtention of such compression ratios would require hundreds of meters of dispersive medium (waveguide, for example), with prohibitively high attenuations. These experimental result represent what we believe to be the first measurements of FM effects in an FEL amplifier.

Active pulse compression using an integrated electro-optic phase modulator

We describe a pulse compression technique that uses integrated electro-optic phase modulators to linearly chirp optical pulses for compression by a dispersive delay line. In contrast to passive chirp techniques such as self-phase modulation, this approach of active pulse compression does not depend on the optical power and thus shows promise for application to low-power solid-state lasers as an alternative to mode locking for realizing compact picosecond sources. We have demonstrated this technique by compressing the pulses from a mode-locked neodymium:yttrium aluminum garnet laser from 100 to 45 ps.