摘要:

This paper extends the theory of parametric upconversion to describe the mixing of two focused optical beams with unequal confocal parameters. The results of this paper have greatest applicability when focusing of one input beam is limited by physical constraints, e.g., damage. The effects of phase matching, walk‐off, and diffraction are treated herein. The analysis shows that if the beams have fixed confocal parametersb1andb2, optimum mixing generally occurs withb2≠b1. If both confocal parameters can be arbitrarily chosen, maximum efficiency occurs withb1=b2= (crystal length)/2.84 in the absence of Poynting vector walk‐off, and withb1≠b2in the presence of walk‐off. For weak focusing upconversion efficiency is written in a closed form which shows explicitly the effect of walk‐off.

ISSN:0021-8979    

DOI:10.1063/1.327353

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The stability of circular waveguide modes perturbed by a relativistic electron beam is investigated. The electron beam propagates along the waveguide and is guided by an applied uniform axial magnetic field. The electron beam is represented by a distribution of rigid rotators all having the same energy and Larmor radiusrLwith their guiding centers centered on a circle or radiusRbaround the guide axis. Numerical results are presented giving a general view of the competition between synchronous and cyclotron instabilities for TM and TE modes as a function ofrLandRb.

ISSN:0021-8979    

DOI:10.1063/1.327317

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We find that the onset of instability in many GaAs DH lasers that are capable of self‐induced modulation is always preceded by the strong emission of noise. The longitudinal optical‐mode width is fairly narrow, typically 0.1–0.3 A˚, when the optical power contains noise. It is only after the optical power exhibits coherent self‐induced modulation that the apparent longitudinal mode width increases to 1–2 A˚. This apparent increase in longitudinal mode width is attributed to a wavelength that changes periodically (sinusoidally, for small signals) with time. The wavelength oscillation is due to variations in refractive index brought about by oscillations in the carrier concentration. The implication is that in these lasers, the instantaneous longitudinal optical mode width is relatively narrow regardless of the temporal instability of the light output. In addition, it is shown analytically that there is a critical noise level above which a laser becomes unstable, i.e., exhibits coherent self‐induced modulation.

ISSN:0021-8979    

DOI:10.1063/1.327326

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Analytical results for the bistatic scattering coefficients and the backscattering cross sections have been derived for active remote sensing of earth terrain with the model of bounded random media which accounts for volume‐scattering effects. It is found that as a result of the effect of the second boundary, the horizontally polarized return &sgr;hhcan be greater than the vertically polarized return &sgr;vv, whereas for a half‐space random medium &sgr;vvis always greater than &sgr;hh. We illustrate by matching the theoretical results with experimental data collected from vegetation field.

ISSN:0021-8979    

DOI:10.1063/1.327335

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The dependence of the infrared laser power produced by a hollow‐cathode copper ion laser on the He and Ar pressure is reported. An argon partial pressure of 1 mbar is found to be optimum and nearly independent of the helium partial pressure and discharge current. The optimum He pressure is about 25 mbar, dependent on the discharge current. A simple rate equation model is given and compared to the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.327301

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Four‐wave parametric amplification is discussed when the incident pump frequency is close to a two‐photon resonant transition in the material. Expressions for the amplification factor are obtained both under steady‐state and pulsed excitation and also for a nonmonochromatic pump. For ultrashort‐pulse excitation an ’’energy theorem’’ is derived and discussed. In steady state, expressions for optimum frequency and intensity are obtained. The amplification factor under broad‐band excitation decreases with increasing pump linewidth.

ISSN:0021-8979    

DOI:10.1063/1.327306

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Observations of optically induced crosstalk drift in LiNbO3waveguide directional coupler switches at 0.633‐ and 1.06‐&mgr;m wavelengths are reported. At 1.06 &mgr;m, crosstalk has been observed to remain below −25 dB for optical powers of 1 mW. The drift at 0.633 &mgr;m is explained in terms of the photorefractive effect of LiNbO3.

ISSN:0021-8979    

DOI:10.1063/1.327307

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Model calculations show that chemical reactions which take place in the active medium of a photolytically pumped iodine laser limit the efficiency with which pump photons are utilized and convert significant amounts of the starting materialRI to the unwanted by‐productsR2and I2. Laser‐ and rf‐discharge‐based methods for regenerating starting materials from by‐products are evaluated experimentally. For economical operation of large iodine laser systems, CF3I is presently the best starting material, and a pulsed rf‐discharge technique is presently the best one for chemical regeneration. The absorbed energy required to regenerate one CF3I molecule using pulsed rf‐discharge techniques is 5.8 eV.

ISSN:0021-8979    

DOI:10.1063/1.327308

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Photoluminescence (PL) measurements using two different incident photon energies (one, higher than both GaAs and AlxGa1−xAs band‐gap energies: indirect excitation; the other, higher than GaAs band‐gap energy but less than Ga1−xAlxAs band‐gap energy: direct excitation) have been conducted on proton‐striped double heterostructures (DH) for cw lasers. These measurements performed inside and outside the stripe regions gave the following results: the luminescence from the regions inside the stripe, when measured under indirect excitation conditions is shown to be affected by the proton bombardment; also a simple heat treatment of these layers is found to restore this luminescence to a large extent. Some experimental evidence assuming the presence of nonradiative centers localized in the neighborhood ofP‐AlxGa1−xAs (confinement layer) andp‐GaAs (active layer) heterointerface is presented and discussed.

ISSN:0021-8979    

DOI:10.1063/1.327401

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The plasmadynamic recombination laser concept is verified experimentally in a high‐power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4pto 4sAr II transitions are established by collisional‐radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of seven such transitions, 5145, 4880, 4764, 4727, 4658, 4579, and 4545 A˚, is observed spectrophotograpically and photoelectrically over the entire 1‐msec discharge.

ISSN:0021-8979    

DOI:10.1063/1.327402

出版商:AIP    

年代:1980

数据来源: AIP