摘要:

It is pointed out that the condition &Dgr;Qout=0 cannot be taken as the criterion of perfect regeneration for a magnetic Ericsson cycle, but &Dgr;CH=0 can. By using the criterion, the regenerative performance of the magnetic Ericsson refrigeration cycle is discussed. Some new characteristics of the cycle are expounded. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360035

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ultrathin dielectrics (<4 nm) were prepared by both growing and annealing in a nitric oxide (NO) ambient, using rapid thermal processing at different temperatures for various lengths of time. Compositions and residual nitrogen contents in various dielectrics were studied using x‐ray photoelectron spectroscopy (XPS). The XPS depth profiles show that the nitrogen distribution of NO grown films is different from those that are NO‐annealed (an initially grown pure oxides annealed in NO), N2O‐grown and N2O‐annealed (an initially grown oxide annealed in N2O) oxynitrides. The nitrogen distributes evenly throughout the dielectric with an atomic percentage of around 5.4 at. % for the NO‐grown sample, while the nitrogen concentration is lower at the dielectric surface and piles up at the dielectrics/silicon interface with a peak of 5 at.% for the NO‐annealed oxides. Deconvolution of Si 2p and N 1s XPS spectra has been used to study the bond structures. Both Si≡N and Si‐N=H2bonds have been found in the NO‐grown and NO‐annealed films, the later one is believed to be introduced by hydrogen impurities present in the NO gas or growth environment. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360036

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simplified collisional‐radiative model has been constructed for the system of the ground state, electronically excited stable states, and the ionic state of molecular hydrogen in plasma. Effective rate coefficients have been calculated for production of electrons, molecular ions, protons, and hydrogen atoms from molecular hydrogen. The ratio of the effective ionization rate of molecular hydrogen to the Balmer &agr; photon emission rate and the effective rate coefficients for radiation and energy losses are also presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360037

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We show that a photoconductivity relaxation can strongly influence the magnitude of the ac current induced in a bipolar photoconductor by a vibrating pattern of interference fringes. This occurs for low pattern vibration frequencies if the time of the photoconductivity relaxation is much greater than the dielectric relaxation time. The features predicted by the theory were observed in semi‐insulating GaAs illuminated by a He–Ne laser (&lgr;=633 nm) for vibration frequencies lower than 20 kHz. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360038

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Reshaping effects of ns pulses were theoretically and experimentally investigated using bulk CdTe. The experiments were performed using a 1.064 &mgr;m Nd:YAG laser with pulse duration of 10 ns. We observed that the laser pulses emerging from the sample experienced temporal compression and modulation which were found to be dependent on the input irradiance, the distance from the exit surface of the sample, and the cross sectional area detected. Self‐defocusing and the formation of ring structures were also observed in the transmitted spatial profile and were found to be dependent on the input irradiance and the position of the detector from the sample. In our model we assumed that the free carriers generated by the two‐photon absorption process were responsible for the induced nonlinear change in the index of refraction. As a result, the temporally and radially dependent phase shift encoded to the field that emerged from the sample was the cause of the reshaping effect. The results of our model, for both the spatial and the temporal profiles, are in good agreement with the experimental results. Moreover, the nonlinear parameters deduced from the fitting are in good agreement with previous experimental and theoretical results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360039

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have conducted a detailed study of the thermal stability of Bragg gratings written in hydrogen‐loaded and unloaded germanium‐doped optical fiber. Interference of either continuous‐wave or pulsed ultraviolet light was used to induce the index modulation gratings. Some gratings were kept at room temperature and others were annealed at fixed temperatures for 10–20 h. For temperatures between room temperature and 350 °C, gratings in the hydrogen‐loaded fiber showed significantly greater decay than those in the unloaded counterpart. The ultraviolet‐induced index modulation in hydrogen‐loaded fiber was reduced by 40% after 10 h at 176 °C, whereas it was reduced by only 5% in unloaded fiber under the same conditions. The annealing behavior of gratings written using the pulsed source was identical to that of gratings written with the continuous‐wave source, and the thermal stability of gratings in hydrogen‐loaded fiber did not depend on the magnitude of the index modulation. We also observed that the annealing of ultraviolet‐induced OH absorption in the hydrogen‐loaded fiber was not correlated with the grating decay. Our annealing results show that the species responsible for the index change in the hydrogen‐loaded fiber are less stable than those in the unloaded fiber. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360753

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The ultrafast pump‐probe signal of a two band semiconductor amplifier is theoretically analysed using Maxwell‐Semiconductor‐Bloch equations. It is shown that the coupling of the pump and probe pulse via the probe gain modification significantly contributes to the signal for short delay times between pump and probe. The probe signal exhibits dominant oscillatory interference‐like structures which conceal intensity dependent ultrafast features. Despite the semiconductor is described with a two band model which does not include free carrier absorption and two photon absorption the results are qualitatively similar to those of recent experiments. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360040

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Complementary modulation involving dynamic carrier heating along with carrier injection is reported as means for the picosecond pulse shaping in a gain‐switched semiconductor laser. By numerical simulation based on the earlier developed model of a GaInAsP/InP laser operating in the 1.55 &mgr;m wavelength, we show that it is possible to produce the ideal‐shaped low‐chirp high‐intensity optical pulses at multi‐Gbit/s repetition rate. A three‐terminal laser device, in which hot electrons with well‐defined and tunable energy are injected by resonant tunneling, is proposed to implement this modulation technique. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360041

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Using a U2+:CaF2passiveQ‐switch for the Er:glass laser, 20 ns, 3 mJ pulses were obtained. This is the shortest duration passiveQ‐switched pulse obtained for this laser without intracavity focusing and without optical damage. The measured U2+:CaF2absorption cross section and relaxation lifetime are compared with those of U2+:SrF2and U2+:BaF2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360042

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this paper we examine the effect of coupling between the wells on the differential gain. We find, as for the gain peak, the differential gain at the gain peak is not a monotonic function of the barrier thickness. For relatively thick barriers inclusion of coupling reduces the differential gain but as the barrier gets thinner the differential gain can be significantly enhanced or suppressed. We also compare our calculations with those for single quantum well to show how the enhancement in differential gain in the multi quantum well laser, due to reduced state filling and higher modal gain is affected by well coupling. Without losing generality, the model assumes the quantum well region to be electric field free. Numerical examples are presented for a GaAs/Al0.2Ga0.8As double quantum well system. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360043

出版商:AIP    

年代:1995

数据来源: AIP