Gain Modification Research Articles

Theory of coherent phenomena in pump-probe excitation of semiconductor amplifiers

The ultrafast pump-probe signal of a two band semiconductor amplifier is theoretically analysed using Maxwell-Semiconductor-Bloch equations. It is shown that the coupling of the pump and probe pulse via the probe gain modification significantly contributes to the signal for short delay times between pump and probe. The probe signal exhibits dominant oscillatory interference-like structures which conceal intensity dependent ultrafast features. Despite the semiconductor is described with a two band model which does not include free carrier absorption and two photon absorption the results are qualitatively similar to those of recent experiments.

Pump depletion through coherent energy transfer in semiconductors

Experimental and theoretical study of multiwave mixing in semiconductors shows that a pump beam may be depleted through coherent energy transfer by a probe with either positive or negative pump/probe detuning. The gain modification is a sum of symmetric and antisymmetric parts associated with on-resonant and off-resonant effects, respectively. The intracavity probe power required for a given pump depletion is linearly dependent on detuning. Laser mode depletion causes mode switching that gives polarization and frequency conversion with high signal gain and high contrast.

A high-rate, high-resolution asymmetric wire chamber with mustrip readout

We have investigated the properties of an asymmetric wire chamber with cathode strip readout. The use of a small gap between the anode plane and the cathode plane and of an electric field configuration provide fast removal of the positive ions produced in the avalanche process and restrict the area of the induced signal on strips engraved on the cathode plane. We can thus contemplate using digital readout for these strips and still have good position resolution, or use analog readout for high spatial resolution. The detector can operate at very high gas gain (10 5; thus with a small gap of 2 mm we can achieve full efficiency for minimum ionizing particles. We have measured no gain modification at a rate of 2 × 10 5 particles mm −2 s −1 at a gain of 10 4 with a distance of 600 μm between anodes and cathodes and 500 μm between anode and cathode field wires.

Acceleration of coherent transfer of energy by stimulated emission and absorption.

Coherent transfer of energy (CTE) gives rise to a new peak and dip in the probe gain spectrum that move proportionally with the intracavity injected power showing that stimulated emission and absorption significantly speed up the semiconductor response. Gain modification is seen in two nondegenerate, cross-polarized modes of a microcavity laser when light is injected into only one mode, giving strong evidence for the CTE origin of the gain asymmetry

Music signal time reverse effect apparatus

First Page

Noise suppression system

An improved noise suppression system (400) is disclosed which performs speech quality enhancement upon speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification. The noise suppression system of the present invention includes a background noise estimator (420) which generates and stores an estimate of the background noise power spectral density based upon pre-processed speech (215), as determined by the detected minima of the post-processed speech energy level. This post-processed speech (255) may be obtained directly from the output of the noise suppression system, or may be simulated by multiplying the pre-processed speech energy (225) by the channel gain values of the modification signal (245). This technique of implementing post-processed signal to generate the background noise estimate (325) provides a more accurate measurement of the background noise energy since it is based upon much cleaner speech signal. As a result, the present invention performs acoustic noise suppression in high ambient noise backgrounds with significantly less voice quality degradation.

A model system for motor learning: adaptive gain control of the blink reflex.

An important aspect of the control of movement is how the nervous system produces adaptive gain modification. To investigate this problem in a simple motor system, we studied lid movement and orbicularis oculis muscle activity in human and rabbit subjects during adaptation of reflex eye blinks. The gain of the reflex could be increased or decreased, depending upon the nature of the adaptive stimulus. Since these gain changes could persist upon removal of the adapting stimulus, adaptation appears to result from a modification of the neural program subserving the blink reflex. The orbicularis oculis electromyogram revealed that the neural modifications producing adaptive gain changes predominantly altered the longer latency components of the reflex, while the short latency components remained unchanged. Moreover, in two other paradigms that modulate the gain of reflexes, habituation and reflex modification, similar changes also occurred primarily in the longer latency components of the blink reflex. This result suggests that modification of neurons in longer latency, indirect pathways, may underlie different forms of motor learning.

Automated data acquisition and analysis of neural evoked potentials

A software system to collect, analyze and store trains of neural evoked potentials is presented. Real-time waveform capture permits sampling of a variable-duration data window of 6 to 399.6 ms with a sample delay accurately adjustable up to 1 001 ms (20 μs resolution). The digitized representation of each waveform is stored for individual analysis. Off-line processing determines 17 parameters of each waveform, including an arrow-selected amplitude and time. Individual processing of waveforms preserves all degrees of freedom for statistical analysis across waveforms. Ensemble averages may optionally be formed from the individual waveforms with processing performed on the averaged responses. The software provides MENU-selectable support functions including stimulus-to-artifact timing, storage and retrieval of data and calculated parameters, digital display of waveforms, data calibration and gain modification, table referenced data editing, file management, simple statistics, hardcopy output, and optional database interfacing with output formatted for compatibility with a statistics package (SAS).

On-line analysis of neuromuscular bioelectric potentials

A computer system is presented which provides for on-line data capture and analysis of evoked end-plate potentials and action potentials, and on-line data capture with off-line analysis of spontaneously occurring miniature end-plate potentials at the end-plate region of the neuromuscular junction. Sampling of evoked waveforms begins after an adjustable delay following the stimulus. Spontaneously occurring waveforms are captured by ‘freezing’ the contents of a circular buffer. The software provides MENU selectable support functions including storage and retrieval of data and calculated parameters, analog and digital display of waveforms, data calibration and gain modification, data editing, file management, and hardcopy output. Calculated parameters of the waveform are optionally placed in a data base file by the analysis programs. The data base may be used for editing, arithmetic operations, and subsetting of variables as well as statistical analysis and plotting of any selected variables.

Interaction of laser light waves by dynamic stark splitting

The spectral splitting of an optical transition by a present light wave on a coupled transition of higher frequency results in a gain modification when even the atoms are widely distributed in velocity. An experiment reveals a narrow-band optical nonreciprocity.