摘要:

The ultimate strength of laser‐drawn silica fibers has been found to be related to the velocity of drawing and the tension in the fiber required to maintain it. We find that when the uncoated pristine fiber tension during drawing exceeds about 80 g for a 110‐&mgr;m fiber there is a dramatic decrease in strength (coated fiber). Dimensional analysis of the laser‐drawing process indicates that for this particular system the fiber tension should be proportional to the cube of the drawing velocity. This is confirmed experimentally for fibers drawn at a variety of tensions and speeds of 0.4 and 1.0 m/s.

ISSN:0021-8979    

DOI:10.1063/1.325411

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Considering both the real and imaginary parts of the dielectric constant to be intensity dependent, we have investigated the self‐focusing of a Gaussian laser beam in a plasma. The mechanism or nonlinearity considered herein is the ponderomotive force or heating mainly determined by collisions of electrons with heavier particles. An equation for the beamwidth parameter and an expression of the axial intensity have been obtained in the WKB(J) and paraxial approximations. It is seen that the effect of nonlinear absorption on self‐focusing is significant. Consideration of nonlinearity in absorption predicts focusing of a laser beam (under certain conditions) even when the linear‐absorption approximation would predict defocusing of the beam. The results reduce to the corresponding analytical results reported earlier, when the intensity dependence of the dielectric constant is neglected. The technique adopted in the present investigation for solving the wave equation in the presence of nonlinear absorption is equally applicable to media other than a plasma.

ISSN:0021-8979    

DOI:10.1063/1.325412

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Small‐signal gains as high as 1.5&percent; cm−1have been measured in a TEA‐CO2amplifier on the 00°2‐ (1001, 0201)I,IIsequence bands. The ratio of the gain coefficient of the sequence bands over the gain coefficient of the regular bands has been observed to be independent of either the CO2or He proportion in the gas mixture. It has also been found to increase with the electrical energy dumped into the active medium and to reach a value of 1/3 at an excitation density of 140 J/l. Gain on the sequence bands has been found to be responsible for the anomalously high gain coefficient that is measured at low J values of theRbranch of the regular 9.4‐&mgr;m transition in TEA amplifiers.

ISSN:0021-8979    

DOI:10.1063/1.325413

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An improved phenomenological model of the electrical and optical characteristics of semiconductor heterostructure injection lasers is analyzed with emphasis on the nonlasing‐to‐lasing phase transition. The model includes both radiative and nonradiative carrier recombination, as well as electron‐photon coupling. Recently developed approximations of the Fermi‐Dirac integral are used, and they allow closed‐form solutions of the electron and photon rate equations to be obtained—even though the carrier populations are highly degenerate near lasing threshold. Because of the detailed information which harmonic‐voltage amplitudes provide, calculation of the functional forms of the voltage derivatives of the devices is emphasized, and expressions for the height and width of the second‐derivative peak, and for the slope at threshold of the first derivative, are obtained. The effects of carrier degeneracy and of nonradiative recombination are explicitly displayed, and both are found to be important in modifying the values of the parameters entering the traditional form,i=ir exp(qV/mkT), of the forward‐conduction current‐voltage relation. In (Al,Ga)As stripe‐geometry lasers values ofm?2 are found to be reasonable.

ISSN:0021-8979    

DOI:10.1063/1.325422

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A sensitive F2absorption diagnostic technique was developed by which a difference in absorption sensitivity of &Dgr;I/I0=10−4can be determined. This value corresponds to an F2pressure–path‐length product of 0.215 Torr cm at 300 K. The method was applied to an HF (DF) chemical laser flow and resulted in measured average nozzle‐exit values (&agr;) of from 0.4 to 0.5 from a totally dissociated plenum, indicating a large degree of nozzle wall recombination.

ISSN:0021-8979    

DOI:10.1063/1.325423

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A sensitive F2absorption diagnostic technique was used to determine F2densities in the flow of a 10.2‐cm‐long combustion‐driven chemical‐laser nozzle. The diagnostic device was demonstrated to be readily transportable and operable in a combustion‐driven chemical‐laser field environment. Cold‐ and hot‐flow measurements up to 970 K plenum temperature (i.e., no F2dissociation cases) were in agreement; hence, the measurement technique appears to be reliable. The use of C2H4as a combustor fuel did not result in particulate absorption or scattering of sufficient magnitude to affect the measurement. The flow dissociation level (&agr;) was ≳0.8 for this nozzle. The measurement sensitivity achieved in these tests was &Dgr;I/I0=6×10−4, which corresponds to an F2density of 6.76×10−6mole/l (i.e., 0.127 Torr F2at 300 K) for a 10.2‐cm path length.

ISSN:0021-8979    

DOI:10.1063/1.325424

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Optimum conditions for the preparation of CdTe with minimum absorption at 10.6 &mgr;m are determined, paying attention both to type and concentration of dopants and the conditions of annealing. Doping with indium and annealing at 700 °C followed by quenching led to material with the smallest absorption coefficient at 10.6 &mgr;m of 8×10−4cm−1.

ISSN:0021-8979    

DOI:10.1063/1.325425

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A 4‐mm gap uv preionized CO2laser has been developed, which operates at pressures ≲ 12 atm using relatively low voltages. Studies of the small‐signal gain and laser‐performance characteristics are reported.

ISSN:0021-8979    

DOI:10.1063/1.325426

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Mirror‐surface‐damage thresholds are calculated analytically for two temporal pulse forms relevant to laser‐fusion experiments; a truncated Gaussian and the ’’ideal’’ isentropic pulse. The results show that 20&percent; more laser energy/cm2may be handled using a two e‐folding Gaussian of the same FWHM as a square pulse of equal peak power. The surface‐temperature rise is given in completely closed form for the isentropic pulse and applied to a conceptual laser‐fusion design.

ISSN:0021-8979    

DOI:10.1063/1.325427

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A peak density of electronically excited free radical NF(b1&Sgr;+) of 5.6×10−10mol/cm3has been produced in a subsonic flow by means of intracavity pulsed iodine laser pumping of ground‐state iodine atoms and subsequent energy transfer of this electronic energy to NF(a1&Dgr;) free radicals. This concentration represents a 30‐fold increase over previously reported steady‐state concentrations and supports the promise of the NF(b1&Sgr;+) species as a potential laser candidate.

ISSN:0021-8979    

DOI:10.1063/1.325428

出版商:AIP    

年代:1978

数据来源: AIP