摘要:

Energy transfer between chromium and rare‐earth ions in YAlO3was investigated from fluorescence excitation spectra and fluorescence decay studies. Rare earths examined include Nd3+, Ho3+, Er3+, Tm3+, and Yb3+. Chromium—to—rare‐earth transfer was observed in all cases; evidence of rare‐earth—to—chromium transfer was also observed for Ho3+. Phonon‐assisted transfer rates are dependent on the energy mismatch of the transitions for the two ions involved. The efficiency of the Cr3+→ Nd3+energy transfer in YAlO3was measured at 300°K and found to be greater than in Y3Al5O12for comparable dopant concentrations. Use of chromium as a sensitizer for rare‐earth fluorescence and laser action is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662895

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The absorption characteristics of COF2both internal and external to the optical resonator of a CO2laser were investigated over pressure ranges 1–26 Torr. Injection of small amounts of COF2into the flow of an operating transfer chemical laser resulted in significant reductions in laser power. The absorption coefficient for COF2was obtained from experiments using a CO2laser with a line selection capability. For pure COF2in the pressure range 1–10 Torr, the strongest absorption was on theP(24) line yielding an absorption coefficient of — 0.005 cm−1Torr−1. When the COF2was diluted with N2, the absorption was found to decrease as the operating laser line moves away from the COF2absorption band centered at 965 cm−1(10.36 &mgr;m).

ISSN:0021-8979    

DOI:10.1063/1.1662896

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In a new concept for an optically regenerativeQswitch which is described, the oscillation of the laser with the cavity closed is sensed by a fast photodiode whose output signal opens the electro‐opticalQswitch. The threshold of the laser as a function of the modulator voltage is theoretically investigated; the empirical results obtained with a YAG:Nd3+laser agree well with theory. The advantages offered by the optically regenerativeQswitch are the easy controllability of the peak power of the giant pulses by way of the modulator voltage and the excellent reproducibility of the giant pulses. The experiments revealed the variations between pulses to be less than 3%. Thus the optically regenerativeQswitch is practical for all giant‐pulse lasers whose emission is required to be highly stable.

ISSN:0021-8979    

DOI:10.1063/1.1662897

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In this study of Zn‐diffused red‐emitting diodes, measurements of emission spectra,I‐Vcharacteristics, electroluminescence (EL) saturation, electron diffusion lengths, and photocapacitance have been compiled. Two factors which contribute to the observed low EL efficiency of diffused diodes have been identified. One is the presence of deep level centers, as indicated by large space‐charge recombination currents. The other is a relatively small product of the Zn&sngbnd;O pair concentration and the electron diffusion length, which determines the EL level at Zn&sngbnd;O pair saturation. Results from photocapacitance measurements indicate that for diffused diodes, the oxygen, and hence the pair concentration, is smaller by a factor of 2–3 than that found in double liquid‐phase epitaxy (LPE) diodes. The effects of an optimized annealing procedure (750°C for 8 h, followed by 525°C for 16 h) were also identified. The 750°C anneal primarily reduces the deep state concentration, whereas the 525°C annealing results in increased Zn&sngbnd;O pair concentrations.

ISSN:0021-8979    

DOI:10.1063/1.1662898

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The impulse reaction resulting from the in‐air irradiation of aluminum by a high‐intensity pulsed CO2laser is experimentally examined in this study. Power densities of the order of 107−108W/cm2are obtained for focused beam energies between 100 and 700 J and pulse durations of between 15 and 50 &mgr; sec. The targets are mounted in a sensitive pendulum in order to measure the total recoil impulse. The time history of the impulse during irradiation is determined by an interferometric technique. In addition, thermocouples are used to monitor the rear surface temperature of the thin (0.05 cm) targets. The thermal and mechanical response of the target is dominated by the effects of a high‐intensity leading edge of the laser pulse. The precursor spike generates an opaque plasma at the target surface which effectively shields the target from the incident energy. Impulse and pressure transmitted to the target are related, therefore, to reaction of the expanding plasma against the target surface. Impulse coupling coefficients (I/E) between 5 and 7.8 dyn sec/J are measured for this mechanism of impulse production. The major contribution to the total impulse is associated with the plasma pressure during the initial stages of the plasma‐surface interaction. The peak pressures generated during this time are found to depend on the second power of the initial beam intensity. It follows that the corresponding impulse coupling coefficients should increase linearly with beam intensity. However, a net increase inI/Eis not realized at higher beam energies because of absorption losses (air breakdown) along the beam path.

ISSN:0021-8979    

DOI:10.1063/1.1662899

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The existence of metal oxides at the surface of a metal irradiated by an intense laser beam leads to partial absorption of the incident radiation in the blow‐off vapor due to vibration‐rotation bands which exist in the vicinity of the laser frequency. We present calculations for the vibration‐rotation bands of SiO, FeO, AlO, and TiO in the 10.6‐&mgr; range for application to CO2laser interaction. The absorption coefficients are calculated by use of a just overlapping line model. The range of validity of the model is established by performing line‐by‐line calculations in the vicinity of a typical laser line. The absorption coefficients are then supplemented with an equilibrium chemistry model for laser interaction with Al2O3and SiO2surfaces. These calculations may be used to establish the importance of surface shielding for cases in which the blow‐off vapor exists in the range of temperatures up to about 7000°K.

ISSN:0021-8979    

DOI:10.1063/1.1662900

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The refractive index difference at the GaAs lasting wavelength of[inverted lazy s] 9000 Åhas been experimentally determined, from the measured beam profile, for a range of (AlGa)As&sngbnd;GaAs heterojunctions of practical interest. Good agreement is found with values calculated from the change in band gap with increasing Al in (AlGa)As. We have also shown by direct measurement that the loss of electron confinement atp+‐pheterojunctions follows a thermally activated process with activation energy equal to the difference in band gap at the heterojunction.

ISSN:0021-8979    

DOI:10.1063/1.1662901

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Energy transfer has been observed between trivalent chromium and ytterbium ions in a silicate glass. Optical absorption and emission spectra of Cr3+and Yb3+are presented and show that the chromium emission, which occurs as a broad‐band fluorescence in the near‐infrared, overlaps the ytterbium absorption. Hence Cr3+ions can be used to sensitize YB3+fluorescence. Cr3+‐to‐Yb3+energy transfer was established from the Yb3+fluorescence excitation spectrum and the decrease in the Cr3+fluorescence intensity and lifetime. A decrease in the Yb3+lifetime with increasing Cr3+content was also observed indicating relaxation of Yb3+by back transfer to the faster relaxing Cr3+ions. Measurements of the Yb3+and Cr3+fluorescence lifetimes as a function of temperature and chromium content are reported.

ISSN:0021-8979    

DOI:10.1063/1.1662902

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A triple sandwich of C&sngbnd;Se&sngbnd;C was employed to study the transformation behavior of amorphous selenium by electron microscopy. The electron beam was used as energy source in all experiments. Reversible transformations from crystalline to amorphous Se was observed in well‐defined localized areas. By application of a rapid heat pulse, void formation occurred in amorphous Se. Slow heating caused erasure of the voids by viscous flow. Crystalline Se held at low temperatures (< 50°C) was found to become amorphous by gradual breakdown of crystalline order under electron irradiation.

ISSN:0021-8979    

DOI:10.1063/1.1662903

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Spectral changes in the spontaneous emission from stripe‐geometry GaAs double‐heterostructure junction lasers have been observed to occur during their noncatastrophic degradation under continuous operation at room temperature. As a result of prolonged continuous operation, the optical wavelength for maximum external spontaneous emission increases significantly as the degradation progresses. In some lasers the wavelength shift has been observed to occur only in the emission from one mirror of the laser with the spectral emission from the other mirror remaining unchanged. The observed changes in rapidly degrading lasers are interpreted in terms of the formation of a localized region of high optical absorption within the active region. The absorbing region is identified by visual observation through thensubstrate of a degraded laser as a volume in which little or no spontaneous emission occurs near the lasing wavelength. In addition, the absorption is shown to be dispersive, exhibiting a sharply increasing absorption edge with increasing energy.

ISSN:0021-8979    

DOI:10.1063/1.1662904

出版商:AIP    

年代:1973

数据来源: AIP