Showing papers on "Power density published in 1968"

Nitrogen laser power density and some design considerations

Abstract: : The laser power density and its time history from a pulsed molecular nitrogen laser were calculated using the theory of Ali, Kolb, and Anderson. The dependence of the power density and its duration on the fill pressure and on various parameters of an electric circuit, in which the nitrogen gas acts as a variable resistor, was examined. It is known that the peak power density increases in a circuit with low inductance and high capacitor voltage and that the energy density is optimum at a fill pressure of approximately 30 Torr. Based on these premises and the gain calculations, some design considerations were also studied.

Characteristics of organic dye lasers as tunable frequency sources for nanosecond absorption of spectroscopy

Abstract: The properties of 1, 1' diethyl-γ-cyano-2,2'-di-carbocyanine-tetrafluoroborate (DTCDCT)and 1, 1'-diethyl-γ-nitro- 4, 4'-di-carbocyanine-tetrafluoroborate (DTNDCT) lasers have been investigated. High-efficiency (25 percent) spectral narrowing of the normal 150-A-wide, 2-MW output of DTCDCT (around λ 7600 A) to 150 MW peak power) produces a train of 100 percent modulated mode-locked dye laser pulses whose risetimes ( 75 \times 10^{-3} cm-1of the λ 7699-A resonance line was detected for a ruby laser perturbing field of power density ∼ 30 MW/cm-2.

Nonlinear absorption of light. positive and negative saturation effects in the same absorber

Abstract: The optical transmission of platinum dithizonate dissolved in CCl4 was measured as a function of intensity at 6943 A. When a 35‐nsec pulse is used for excitation the transmission increases from its low‐level value at a power density of 0.1 MW/cm2, goes through a maximum at 10 MW/cm2 and then decreases to its low‐level value at 80 MW/cm2. This material functions effectively as a passive Q switch for ruby and may provide power stabilization as well. A long‐lived cumulative bleaching effect is produced when the output from a non‐Q‐spoiled laser is used for excitation. The transmission behavior of this system at all intensities is discussed in terms of a generalized kinetic mechanism.

A solid state broadband microwave noise source

Abstract: Recent studies of avalanche breakdown have led to a thorough understanding of the noise properties of a stable-burning avalanche discharge in a reverse biased silicon p-n junction. Avalanche diodes specially designed for uniform breakdown are nearly ideal noise sources because of their high noise output, high efficiency, broad bandwidth, low temperature dependence and high reliability. In order to reduce circuit parasitics, volume, and weight we have integrated an optimized avalanche diode with its current regulating bias circuit into a microstrip-line circuit on a ceramic substrate. Such a microwave noise source has a potential frequency range from dc to 18 GHz thus replacing one temperature limit diode and six gas discharge tubes required to cover the same range. The noise source can be biased from an unregulated voltage supply with 20 to 35 v and approximately 30 mA. The following preliminary measurements were obtained: The spectral noise power density was found to be > 30 db above kT from 1 to 11 GHz with a spectral density variation within ± 0.7 db. Tuning out reflections from connectors and adaptors reduced the spectral density variation to less than ± 0.2 db from 2.0 to 5.5 GHz and to less than ± 0.3 db from 8.0 to 11.2 GHz. The stability was found to be better than ± 0.01 db over a 12-hr period and better than ± 0.1 db over a 500-hr period. The temperature dependence, of the spectral power density measured at 2.5 GHz was found to be better than --0.002 db/°C. The dependence of spectral power density on bias voltage was better than -0.005 db/v. To study the reproducibility of diode fabrication we mounted 20 diodes in microwave pill packages. At a bias current of 20 mA the spectral power density at 10 GHz was 33.0 db with a spread of ± 0.15 db for 18 of the 20 diodes.

Perturbations of Microwave Cavity Fields by Time‐Varying Xenon Laser Discharges

Abstract: The effects of a time‐varying complex dielectric constant upon the resonant characteristics of a cylindrical microwave cavity are presented. The cavity resonance equations are developed to consider the influence of small periodic changes in resonant frequency, bandwidth, and cavity‐coupling coefficient upon the microwave power density within the cavity as a function of the probing microwave frequency. Expressions are derived which enable the separate contributions of periodic changes in cavity power density to be extracted from measurements at several microwave frequencies. It is shown that for high‐Q cavities, variations in the sampled microwave cavity fields are due predominantly to shifts in the cavity resonant frequency. By repetitively interrupting the mirror cavity of a 3.51‐μ xenon laser with a mechanical chopping wheel, very small periodic changes are induced in the electron density and collision frequency of the xenon dc discharge due to changes in the laser field strength. The resultant changes ...

Interaction of High-Powered Focused Laser Beam with Exploding Wire

Abstract: A combination of the high electric field intensity attainable with a focused laser beam and the high electric current capability of an electrical pulsed power system is an efficient technique for heating small diameter wires. Measurements have been made on the combined electrical—laser heating of 25-μ-diameter, 6-mm-long bare copper wires. Electrical heating was provided by a 0.05-μF, 20-kV capacitor, discharging through the wire with a frequency of 3 MHz. A ruby laser, generating a single 10-nsec pulse with a peak power of 40 MW, was used for optical heating. With the laser beam focused in a 1000-μ-diameter spot on the wire, a power density of 5.1 × 109 W/cm2, corresponding to an average electric field of 1.4 × 106 V/cm, was measured. The focused laser beam produces a high degree of ionization in the wire material during the “discharge pause.”