摘要:

The rapid degradation at 300°K in the cw regenerative output of stripe‐geometry GaAs double‐heterostructure junction lasers is shown to be a result of the formation of a local optical absorber in the laser cavity. Gain measurements performed on diodes before and after degradation show that the optical loss within the cavity increases during degradation. By observing the (predominantly) spontaneous emission from the active region directly through then‐GaAs substrate, it is confirmed that the increased loss is localized in a region where little or no spontaneous emission takes place at lasing energies. In such diodes, the internal radiative efficiency of the undegraded portion of the optical cavity shows a relatively small decrease compared to the external differential quantum efficiency. When the local absorber extends over a sufficient length of the cavity the electronic gain in the undegraded section is insufficient to overcome the loss and the device ceases to act as a regenerative optical oscillator. Net gain measurements on DH laser devices in which the active region is lightly (≈ 1017)n‐doped indicate that the optical gain increases linearly with current prior to degradation. At lasing threshold the medium exhibits net gain over a wavelength range of 100 Å. After degradation the gain dependence on current can become superlinear due to the saturation of the optical absorber. Estimates on the attenuation constant in the local absorber at low currents give a value of ≈ 60 cm−1at 8800 Å. For pulsed currents close to lasing threshold the attenuation constant increases to nearly 160 cm−1at 8760 Å.

ISSN:0021-8979    

DOI:10.1063/1.1662905

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Experimental data are presented which demonstrate superfluorescent radiation due to stimulated transitions between the lowest‐bound diatomic states of xenon and the repulsive ground state. In this context, superfluorescence describes a condition where, even in the absence of feedback, radiation from the fluorescent medium is dominated by stimulated transitions. The continuum emission spectrum was highly anisotropic and narrowing of the spectrum was observed. The optical gain was greatest at a wavelength of 1730 ± 10 Å, where the experimentally estimated effective gain cross section is 1 × 10−18cm2.

ISSN:0021-8979    

DOI:10.1063/1.1662906

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Temporally and spatially resolved gain measurements are reported for near‐atmospheric CO2:N2:He glow discharges in a contoured planar electrode configuration. When suitably preionized by rows of electrically stressed dielectric interfaces, the entire interelectrode volume is filled with a uniform glow discharge for large ranges of capacitor energy, voltage, and gas pressure. The 10.59‐&mgr;m gain reaches a peak value of 2.8% cm−1in 2 &mgr;sec, and decays exponentially with a 20‐&mgr;sec time constant in near‐optimum laser mixtures of 60 Torr CO2, 180 Torr N2, and 60 Torr He. Peak gain is uniform over the transverse dimensions to within 5%. Mathematical expressions are developed which relate the small‐signal gain to thePandRbranch rotational quantum numbers in a linear fashion. This analysis shows that for optimized laser conditions the 00°1–10°0 population inversion is[inverted lazy s]1.8×1017 cm−3with a rotational temperature of[inverted lazy s]400 °K. This corresponds to a maximum 10.6‐&mgr;m optical storage density of[inverted lazy s]31 J/literand represents[inverted lazy s]17%of the electrical energy input to the discharge.

ISSN:0021-8979    

DOI:10.1063/1.1662907

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The maximum reduction in the average temperature ⟨T⟩z=b−1∫0bd z Tof a slab of thicknessbthat can be obtained in both a short period of time, typically[inverted lazy s]1 sec,and a long period of time (steady‐state approached) without causing material failure is calculated. The slab is originally at a constant temperature, and ⟨T⟩zis the temperature that determines the optical properties of a normally illuminated slab. The results indicate that Ge28Sb12Se60glass can be cooled rapidly enough for use in laser systems at relatively high power levels (several hundred W/cm2) in the pulse mode of operation discussed previously, in contrast to previous beliefs. There is a time constant &tgr;sfor the nonexponential approach of the surface temperatureTsof a semi‐infinite medium to the temperatureTcof the coolant. Consider the thermally thin‐disk case of&tgr;b≪&tgr;s, where &tgr;bis time required for heat to diffuse across the thicknessb, roughly speaking. The value of ⟨T⟩zthen approachesTcexponentially with a time constant &tgr;c, which is much smaller than &tgr;s. For the thermally thick‐disk case of&tgr;s≪&tgr;b,⟨T⟩z[inverted lazy s](t/&tgr;c)Tcfort≪&tgr;s; ⟨T⟩z≃(t/&tgr;b)1/2Tcfor&tgr;s≪t≪&tgr;b; and ⟨T⟩z≃Tcfort≫&tgr;b.The solution to the heat‐flow equation forTis known in simple closed form for the case of a semi‐infinite medium. The result is quite accurate for finite disks, both thermally thick and thin, whent≪&tgr;bis satisfied. For this case oft≪&tgr;b, the maximum value of the magnitude of the stress component |&sgr;xx|(=|&sgr;yy|) is determined by the surface temperatureTsonly. For a given temperature difference across the disk, the maximum value of |&sgr;xx| is less for the case oft≥&tgr;bthan for the case oft≪&tgr;b. Two examples, GaAs and Ge28Sb12Se60glass, are considered.

ISSN:0021-8979    

DOI:10.1063/1.1662908

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The characteristics of tunable Pb1−xSnxTe(0.08⪝×⩽∼0.20)junction lasers are described. The lasers operate cw at liquid‐helium temperatures and for the above alloy compositions, the wavelength is in the 8–12‐&mgr;m region of the infrared. The devices are prepared by antimony diffusion into largep‐type vapor‐grown single crystals. Active region width, gain, and loss parameters are derived from measurements of the current density at the lasing threshold, efficiency, and cavity length dependence of the threshold current. Impurity diffused lasers favor oscillation in high‐order TE modes and some evidence of filamentary lasing was obtained from the device parameters together with a study of far‐field patterns. Results are presented which confirm the model of current tunability of these devices and provide data on refractive index and temperature dependence of the forbidden energy gap in these alloys. Finally, spectroscopic data are presented to show the present limitations and potential of the diode laser for rapid(≪50 &mgr;sec)high‐resolution gas spectroscopy.

ISSN:0021-8979    

DOI:10.1063/1.1662909

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The laser behavior of the Cresyl Violet‐Rhodamine 6G dye system is studied by measurements of the small‐signal gain spectra for various dye mixtures and pump powers. It is found that most of the pump power absorbed by the Rhodamine 6G is transferred to the Cresyl Violet as useful pump power. The experimental results are in good agreement with a simple theoretical model.

ISSN:0021-8979    

DOI:10.1063/1.1662910

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The measurement of Young's modulus as a function of temperature for pressure‐sintered lithium‐doped nickel oxide was found to be a very sensitive method for the determination of the variation of the Ne´el temperature with composition. The low‐temperature value of Young's modulus was found to increase with increased lithium content and the temperature of the modulus anomaly was found to decrease linearly with increased lithium content. This behavior was interpreted in terms of a localized electron theory of antiferromagnetism. Resistivity measurements agreed with the reported results on single‐crystal material. These include a break at the Ne´el temperature, a lower activation energy at higher temperatures than at lower temperatures, and a decrease in the low ‐ temperature activation energy with increasing lithium content. The combined trends in the modulus and resistivity as a function of temperature and impurity level were interpreted in terms of an electron‐acoustic‐mode interaction model which predicts an inverse relation between the elastic modulus and the energy difference between the self ‐ trapped and activated electron states. It was concluded that the success of a quantitatively correct localized electron model appears to depend on the development of a theoretical approach which would simultaneously account for both optical ‐ mode and acoustic ‐ mode interactions.

ISSN:0021-8979    

DOI:10.1063/1.1662911

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Optical transmission properties are described for two types of waveguides formed in AlxGa1−xAs&sngbnd;GaAs&sngbnd;AlxGa1−xAs epitaxial layers. The first consists of long smooth‐walled mesas formed by a masking and etching procedure and the second are obtained using an additional etching step to selectively etch the GaAs layer. The latter structure is potentially useful in forming active devices such as modulators since this structure is self‐masking for contacting of the top layer by conventional evaporation techniques. The waveguide dimensions are typically 1–30 &mgr;m wide, [sine wave] 1 &mgr;m thick, and several mm in length. The transmission measurements are quite similar for both types of guides with attenuation as low as[inverted lazy s]2 cm−1in wide([inverted lazy s]20 &mgr;m)guides but with losses increasing with decreasing width. The loss appears to arise from imperfections and compositional inhomogeneities in the epitaxial layers.

ISSN:0021-8979    

DOI:10.1063/1.1662912

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Controlled adjustment of the bubble domain collapse field has been demonstrated in epitaxial garnet films of nominal composition Y2.6Sm0.4Ga1.2Fe3.8O12using a thermal annealing technique to redistribute gallium ions between the tetrahedral and octahedral sites in the garnet lattice. This technique involves annealing each film at two different temperatures, the first of which establishes equilibrium at a known temperature. Analysis, based on bubble domain theory, shows that the measured parameters after thermal equilibration can be used to calculate the change in saturation magnetization which will lead to the desired values of the bubble domain collapse field. The change in magnetization can be related to the required change in the equilibrium annealing temperature,Ta, from the derivatived(4&pgr;Ms)/dTa. The value ofd(4&pgr;Ms)/dTahas been found to be approximately constant for900≲Ta≲1200 °Cand is equal to0.35≲G/°C. By using this technique, the bubble domain collapse field can be changed by more than 10 Oe with a precision of a few tenths of an Oersted if the annealing temperatures are controlled to a fraction of 1°C.

ISSN:0021-8979    

DOI:10.1063/1.1662913

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Simple domain structures were observed in iron‐silicon and cobalt‐iron single crystals by three techniques using polarized neutrons. The first method involves scanning the specimen with a fine beam and measuring the depolarization suffered by the beam after transmission: it can only detect regions where the magnetization direction deviates from the direction of polarization of the beam, and cannot differentiate domains with antiparallel magnetization. The second method, based on the determination of the ratio of the Bragg‐diffracted intensities when the polarization of a fine beam is reversed, provides, when the specimen is scanned, a map of the domains. The third technique, polarized neutron diffraction topography, provides photographs of the domain structure. The possibilities of these techniques for the observation of domains within bulk specimens are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662914

出版商:AIP    

年代:1973

数据来源: AIP