Showing papers on "Chirp published in 1972"

Analytic Study of Pulse Chirping in Self-Induced Transparency

Abstract: We analyze the phase modulation, or chirping, of coherent lossless light pulses propagating without distortion through resonant absorbers In order to do this, we generalize the pioneering work of McCall and Hahn in two different directions In the first place, of course, we abandon their assumption that the phase of the pulses has no temporal dependence We prove that for slowly varying single pulses, chirping is not possible However, we describe many multiple-pulse trains which are necessarily chirped, even under the slowly varying envelope restriction, and also describe the envelope modulations which produce large chirps We show that certain zero-$\ensuremath{\pi}$ chirped pulse trains are contained as special cases of our general results Our second generalization of the McCall-Hahn work concerns the background material in which the two-level resonant atoms are suspended We allow the host medium to possess significant nonresonant nonlinearities We find that undistorted lossless single pulses are possible in such a medium and that they are necessarily chirped

Charge-coupled-device analogue matched filters

Abstract: Charge-coupled-device shift registers are used to construct filters matched to both a 13-chip Barker-coded p-n sequence and a chirp signal with a time-bandwidth product of 10. The letter describes the design and fabrication of the devices, and presents preliminary operational characteristics of the filters. A 5 MHz chip rate for the Barker code filter is demonstrated

Pulse compression radar

Abstract: An improved digital technique for generating a chirp modulation signal for a pulse compression radar is shown. A stored set of digital numbers having a minimum number of different absolute values of successive samples of the desired modulation signal is processed through a logic circuit to derive a second set of complex digital numbers describing such modulation signal; such second set is then converted to an analog signal which is taken as the chirp modulation signal.

Method and circuit for monitoring and detecting sweep signal failure

Abstract: A method and sweep signal monitoring circuit for protecting scanned electron tubes, particularly high sensitivity imaging devices such as television camera tubes, from damage upon loss of a sweep voltage. A monitoring circuit monitors the sweep voltage and generates, through the use of complementary gating signals, a digital signal having a first signal level for a normal sweep voltage and a second signal level for an abnormal sweep voltage. The second signal level of the digital signal not only indicates loss of the sweep voltage but also indicates undesirable changes in the zero crossing point of the sweep voltage. The signal level of the digital signal is monitored and the detection of the second signal level may result in the inhibiting of the scanning of the tube or in any other suitable protective measures.

Pulse compression techniques in nuclear medicine

Abstract: A high-efficiency "chirped" linear array of pinholes for imaging a distribution of radioisotopes is described. The image is obtained in a coded or scrambled form, and then decoded using a dispersive surface acoustic wave delay line. Results of an optical simulation experiment are presented.

Underwater Acoustic Scattering from Lake Surfaces. I. Theory, Experiment, and Validation of the Data

Abstract: A statistical analysis, based directly on ensemble averages, is made of reverberation data obtained from the wind‐driven surface of a fresh water lake. To produce the reverberation, two types of signals consisting of gated (linear “chirp”) FM or CW pulses, are transmitted with a carrier frequency of 110 kHz. In the CW cases the pulse durations are 0.1 and 1.0 msec. The bandwidth of the FM signals (pulse durations 1.25 msec) is 9.6 kHz, and operation in all instances is monostatic (R@T). In the CW experiment the grazing angle is 22°, and in the FM experiment the grazing angle is 0°. Particular care is taken to insure that a valid sample ensemble is obtained by testing each sample ensemble for independence (from a one‐sample runs test) and homogeneity (by a suitable Kolmogorov‐Smirnov test). A recently developed point scattering model is introduced and adapted to the present experimental geometry to provide a theoretical description of the reverberation and a basis for later comparisons with the data. From this model covariance functions and intensities of the scattered signal are determined and quantitative insight obtained regarding the nonstationarity of the reverberation process.

Frequency Modulation and Transient Effects in the Resonant Propagation of Coherent Light Pulses

Abstract: A theoretical analysis of the propagation of near resonant and linearly chirped light pulses through a resonant medium is presented under the restriction that the pulses are far enough off resonance or weak enough so that they do not significantly alter the atomic populations. If the pulses are of duration comparable to or less than the phase memory time T2 of the atoms, it is found that the transient response of the medium gives rise to amplitude- and phase-modulating effects. Analytic solutions are presented to describe the propagation of an off-resonant pulse which is very short compared with T2 and an off-resonant rectangular pulse. The evolution of a Gaussian pulse having a positive linear chirp is studied numerically.

Variable-bandwidth frequency-modulation chirp pulse compression using a longitudinal acoustic-wave convolver at 1.3 GHz

Abstract: A symmetric V-shaped frequency-modulation chirp is used to demonstrate pulse compression of variable-bandwidth signals centred at 1.3 GHz. The compression device is based upon the nonlinearity in a lithium-niobate longitudinal-wave acoustic delay line. Uniformity of the interaction region is achieved so that the convolution is not spatially weighted.

Television deflection circuit for distortion correction

Abstract: A vertical deflection circuit for a television receiver that utilizes a flat face picture tube in which the radius of curvature of the face is greater than its distance from the deflection center of the scanning yoke. The circuit includes an oscillator and a first wave shaping network for developing a modified sawtooth sweep signal having a flattened trailing portion. A vertical output tube, in response to this modified signal, develops an output signal having a polarity opposite that of the input sawtooth. A feedback circuit couples the output signal to the input of the oscillator and also applies it to a second wave shaping network which includes an integrating circuit for deriving a signal having a parabolic component. The modified sawtooth and the parabolic component are combined to develop an S-shaped signal having modified slope portions at both extremities. The S-shaped signal is utilized as the control signal for the vertical output tube which supplies energizing currents, that are replicas of the S-shaped signal, to the deflection yoke thereby reducing the writing speed of the beam at opposite extremities of its scansion to offset distortion in the raster attributable to the disparity between the screen radius of curvature and the location of the yoke's center of deflection.

A Study of Compressed Spatially Non‐Gaussian Optical Pulses from Mode‐Locked Lasers

Abstract: The effect on the grating‐induced phase and spatial modulations by multiple transverse modes simultaneously present in mode‐locked laser pulses is investigated. Our analysis shows that the dispersions of the grating pair become strongly dependent on wavelength because of the energy exchanges occuring among transverse modes. As a result, the maximum‐intensity trace at the output of the grating is shown to be curved and the grating‐induced pulse‐compression rate is shown to vary significantly across the beam cross section. Also, a discussion is presented relating our analysis to existing experimental data on the wavelength‐dependent chirping rates of mode‐locked laser beams.

Effect of Saturated Frequency Chirping on Mode‐Locked Laser Pulses

Abstract: A dye‐induced nonlinear frequency chirping is analytically shown to have significant modifications on the nature of the output mode‐locked lasers. It is shown that the saturated frequency sweeping is responsible for substantial pulse broadening as well as substructures.

Identification of Earthquakes and Underground Explosions

Abstract: : The report describes the progress of research made for the first six months of FY1972-1973. The research has been concentrated in several areas. Firstly, investigations of Rayleigh Wave dispersion over a continental path have shown a dispersion wave stability that has enabled the development of 'chirp' (or matched) filter techniques. When suitably constructed these filters permit the detection of surface waves with low signal-to-noise ratios, and enable the separation of mixed events. Secondly, array processing techniques in frequency- wave-number space have been significantly improved. Thirdly, a method has been described for correcting the bias in the estimation of body wave magnitudes (m sub b). And, fourthly, two-dimensional model studies have been used to corroborate theoretical predictions of surface wave spectra for an oceanic upper mantle model.