摘要:

An rf wave applied to an optically pumped Na vapor in a high‐density He+N2buffer gas, situated in a magnetic field gradient, can produce localized bright fringes due to local rf magnetic resonance. We examine in this paper the features of optical pumping in a dense alkali‐helium‐nitrogen vapor mixture, and investigate how such systems can be optimized for use as a simple real‐time rf spectrum analyzer (for broadcast rf waves) with a wide frequency range (dc to several GHz). We derive the optimum values of the optical pumping rate, helium density, sodium density, and nitrogen density which are necessary in order to produce sharp, high‐contrast, and bright fringes, and have accurate and unambiguous rf frequency spectra determinations with fast dynamic response. Samples of observed rf frequency spectra are presented, and the observed spectrum of a sinusoidal FM wave compares satisfactorily with the theoretical spectrum. The observed rf resolution bandwidth is about equal to the optical pumping rate, which is about 1 kHz in this study (rf frequency ∼1 MHz). Similar resolution can be obtained in the microwave range.

ISSN:0021-8979    

DOI:10.1063/1.326147

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Calculations are compared with measurements of nanosecond pulses propagating through a large CO2‐laser amplifier system. Both coherence of medium polarization and rotational relaxation are included in the traveling‐wave equations describing pulse propagation in an amplifying or absorbing medium. The basic formalism is derived and adapted to a model of the LASL two‐beam system. Excellent agreement between the calculated and the measured output pulse shape and energy extraction is found. No adjustable parameters influence these calculations since all physical parameters used, as well as the input pulse itself, are derived from measured quantities.

ISSN:0021-8979    

DOI:10.1063/1.326148

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A supersonic purely chemical continuous‐wave HCl laser is described in which nonequilibrium concentrations of atomic chlorine are generated by the branch‐chain reaction of NO with ClO2. The ClO2is injected into a stream of NO in helium immediately upstream of the throat of a slit nozzle. The reacting gases then expand as a free jet into a low‐pressure region where HI is added to rapidly form vibrationally excited HCl. A maximum HCl multiline output power of 35 W is obtained, which represents a chemical efficiency of ∼4.5% based on the total exothermicity of the pumping reaction and the limiting flow rate of HI. An efficient technique for visualizing the flow in the expanded region is described. This technique is based on the visible chemiluminescence resulting from the addition of H2S to the NO/ClO2reaction system.

ISSN:0021-8979    

DOI:10.1063/1.326149

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In this report, we describe a statistical study of the reliability of oxide‐defined stripe‐contact cw injection lasers of (AlGa)As. These devices have one facet coated with Al2O3and one facet coated with an Al2O3/Si dichroic reflector; the lasers are optimized for cw low‐threshold currents at room temperature, with values typically about 50 mA. Lifetests were carried out at 70 °C ambient, in the cw mode of operation with about 5 mW output. Previous lifetests showed that the degradation rate followed a 0.95‐eV activation energy so the 70 °C environment provides a degradation acceleration factor of 190 over that at room temperature. We have found that the device failures follow a log‐normal distribution, characterized by a mean time before failure of 4200 h and a standard deviation of 1.3. This corresponds to a mean time to failure (MTTF) of 106h at room temperature. Failure is defined here as the inability of the device to emit 1 mW of stimulated cw output at 70 °C, and assumes that optical feedback will be employed to adjust the laser current during operation. If a constant‐current drive is envisioned, the failures for a 3‐dB drop in light output also follow a log‐normal distribution with a similar slope (standard deviation=1.1) and a MTTF of 2000 h at 70 °C (500 000 h at room temperature). The failures were found to be mainly due to bulk gradual degradation and not facet or contact failure. Careful study of lasers before and after lifetest showed a significant increase in contact thermal resistance. However, this increase accounts for only a small portion of the nearly 70% increase in room‐temperature cw threshold after failure at 70 °C. After failure at 70 °C, we also noted a degradation in the near‐field and associated far‐field pattern of the laser.

ISSN:0021-8979    

DOI:10.1063/1.326150

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Large‐scale temporal oscillations are observed in the output of high‐energy flowing cw CO2lasers, causing appreciable reduction in power output and optical‐beam quality. The modulation is linked to wavelike disturbances in the optical cavity which propagate either along the flow axis or transverse to both optical and flow axes. These waves, caused by an unstable interaction between the radiation field and the laser medium, are referred to as the mode‐medium instability. The present analysis examines transverse waves that are associated with interactions between optical resonator modes and acoustic resonator modes. The modes interact through fluctuations in gain and refractive gradients due to the heat release during lower‐laser‐level collisional deactivation. This can lead to unstable acoustic wave growth. Two important propagation numbers,k0andkm, emerge from the analysis. They define a region of unstable wave growth forkbetweenk0andkm. The instability growth rate is maximum nearkmand is zero atk0. It appears possible to minimize the instability by adjusting the laser parameters so thatk0andkmcoincide.

ISSN:0021-8979    

DOI:10.1063/1.326151

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The image formation in photoprojection and contact printing systems is frustrated by the existence of standing waves in the photosensitive resist layer, and the reflections will cause blurring of the image. This problem is most severe for coherent illuminated systems and for realization of patterns in highly conducting substrates such as metals. A number of materials which can be used as spacers to reduce the reflected wave in the resist are theoretically investigated and experimentally tested. The use of a spacer reduces exposure time and increases the edge sharpness of the resist’s intensity profile.

ISSN:0021-8979    

DOI:10.1063/1.326152

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A direct optical marking process based on dye diffusion in a dye‐polymer system is described. Relevant thermal and spectral properties of dye and substrate were investigated. Typical marking performance is outlined for magenta dye films on Mylar. Marked bits were submicron in size and energy‐density requirements below 100 mJ/cm2were observed. A mechanism of the process is proposed and good quantitative agreements are obtained between experimental and predicted power thresholds and sensitivities.

ISSN:0021-8979    

DOI:10.1063/1.326153

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The periodic multilayers of dielectric materials such as polystyrene/collodion or polystyrene/polyvinyl alcohol were fabricated by means of alternately dropping these solutions onto a spinner. As these materials are slightly elastic, a large shift of the center of the Bragg reflection by 650 A˚ toward shorter wavelength is obtained by the compression of the multilayer. A periodic length &Lgr; is controlled by adjusting both the rotation speed of the spinner and the concentration of the solutions.

ISSN:0021-8979    

DOI:10.1063/1.326154

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Theoretical models of nuclear‐pumped lasers are of interest for the purpose of system optimization and identification of new and more efficient nuclear‐pumped laser systems. A first‐order model of the3He‐Ar 1.79‐&mgr;m laser is developed, compared to experimental results, and used to explain the qualitative features of this system. The results indicate that direct excitation of the argon upper level is at best very inefficient for population inversion. For argon concentrations which give the most efficient laser operation, the3He(n,p)3H energy is used to produce atomic helium ions that quickly convert into helium molecular ions. These molecular ions subsequently form argon atomic ions through charge transfer. The dominant pumping mechanism is collisional‐radiative recombination of the argon atomic ion and subsequent radiative cascading into the upper laser level. The formation of argon molecular ions is in competition with argon atomic ion recombination; this combined with the dissociative recombination of argon molecular ions into the lower laser level terminates laser action for argon concentrations above 20%.

ISSN:0021-8979    

DOI:10.1063/1.326142

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Longitudinal and shear mechanical relaxation data are reported for a hydration of 20% of synthetic diethylamine melanin. The longitudinal attenuations per wavelength &agr;&lgr; at frequencies between 1 and 5 MHz show an enormously large amount of absorption above room temperature. The amount &agr;&lgr;/2&pgr;=0.55–0.95 at a temperature of 60 °C in the frequency of 1 MHz has never been found in usual polymeric substances where &agr;&lgr;/2&pgr;∼0.1. The longitudinal data are interpreted in terms of a combined relaxation and resonance process. Measurements of the shear impedance in the temperature range from −10 to +60 °C, with frequencies ranging from 5.2 to 362 MHz, indicate a distribution of relaxation times, represented by the Davidson‐Cole spectrum. Temperature dependency of limiting shear modulus is found to obey the Hirai‐Eyring equation.

ISSN:0021-8979    

DOI:10.1063/1.326143

出版商:AIP    

年代:1979

数据来源: AIP