The expansion velocity of the luminous front of a plasma plume created by a giant pulse laser has been measured both as a function of time during the laser pulse and as a function of position in front of the pyrolitic graphite target. The initial velocity of the vapor appears to agree with the sublimation temperature of pyrolitic graphite. The subsequent vapor absorption of laser radiation produced peak final expansion velocities of 7 × 106 cm/sec. The luminous front was found to accelerate from 4.8 × 105 to 7.0 × 106 cm/sec within a 0.3-cm distance for a laser energy density of 700 J/cm2.
The Missile Defense Agency's Advanced Technology Office is developing advanced passive electro-optical and infrared sensors for future space-based seekers by exploring new infrared detector materials. A Type II strained layer superlattice, one of the materials under development, has shown great potential for space applications. Theoretical results indicate that strained layer superlattice has the promise to be superior to current infrared sensor materials, such as HgCdTe, quantum well infrared photodetectors, and Si:As. Strained layer superlattice-based infrared detector materials combine the advantages of HgCdTe and quantum well infrared photodetectors. The bandgap of strained layer superlattice can be tuned for strong broadband absorption throughout the short-, mid-, long-, and very long wavelength infrared bands. The electronic band structure can be engineered to suppress Auger recombination noise and reduce the tunneling current. The device structures can be easily stacked for multicolor focal plane arrays. The III-V semiconductor fabrication offers the potential of producing low-defect-density, large-format focal plane arrays with high uniformity and high operability. A current program goal is to extend wavelengths to longer than 14 µm for space applications. This paper discusses the advantages of strained layer superlattice materials and describes efforts to improve the material quality, device design, and device processing.
The temperature of a laser-heated carbon plasma, formed by the interaction between a Q~switched ruby laser and a pyrolytic graphite slab, has been measured using interferometric, spec~roscopIC, and energy conservation techniques. Results indicate that the maximum plasma temperature IS less than 10 eV. A method of determining whether the plasma is in thermodynamic equilibrium is employed and indicates that at laser fluxes of 10 9 W /cm 2 the plasma is not in LTE with the electron temperature nearly an orderof-magnitude larger than the plasma temperature. For fluxes of 1010 W jcm 2 , however, the plasma appears to approach a state of thermodynamic equilibrium with a temperature of 2eV.
This paper deals with the subject of laser hazards, laser hazards control, and laser safety practices in the laboratory. Laser hazards, which fall into four categories (radiative, electrical, explosive, and toxic) are described in detail. Following this, the status of federal regulations which seek to define laser hazards control and safety standards is briefly reviewed. The paper concludes with a brief discussion of laser safety goggles and a list of suggestions of laser safety practices intended to assist those who are concerned or involved with the use of lasers in a laboratory environment.
The uncertainty principle is used to derive the ultimate spectral width of the laser beam. The resulting expression is the Schawlow–Townes formula. The derivation is simple and can readily be incorporated into an introductory course on lasers. The derivation can also be used in a modern physics course to illustrate the usefulness of the uncertainty principle.
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