摘要:

The contributions of space charge to chromatic and trajectory aberrations of accelerating electrons in a laser‐illuminated photoelectron microscope are calculated. Average and fluctuating components of the electrostatic forces on the particles are considered spearately. The average forces produce a magnification change but no chromatic spread. Fluctuating effects include relaxation of potential to kinetic energy in a beam obeying Poisson emission statistics, and transverse‐to‐longitudinal velocity relaxation by multiple scattering. The potential energy relaxation is treated in a new way by modifying the Poisson distribution with position along the beam axis. The field fluctuations produce both chromatic and trajectory spreading effects, the latter being much larger at high currents. The resolution limit is about 500 A˚ for 30‐kV electrons in a beam of 1‐A/cm2current density.

ISSN:0021-8979    

DOI:10.1063/1.329216

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Using an algorithm for solution of the Poisson‐Vlasov equations for ions extracted from a plasma, an electrode shape is considered which has high optimum perveance and low beam divergence.

ISSN:0021-8979    

DOI:10.1063/1.329217

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We present a new technique for cooling heavy‐ion beams. The discrete absorption spectrum of the ions and the transverse Doppler shift distinguish the transverse direction of velocity and cool the ions by photon absorption. We evaluate the total energy and time requirements for a particular example relevant to heavy‐ion fusion.

ISSN:0021-8979    

DOI:10.1063/1.329218

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A dispersion relation which includes finite axial wavevectors,k, is derived in the rest frame of the beam where the instability is assumed to be electrostatic. The dispersion relation is obtained in the lab frame by a Lorentz transformation. The instability is found to have a finitekbandwidth with the most unstable mode occurring atk≠0. The growth rate for the most unstable mode is found to be reduced by approximately 1/&ggr;2from the nonrelativistic result while the real frequency of this mode remains virtually unchanged. The effects of finitevzshear, which are left out of the analysis, are estimated and discussed.

ISSN:0021-8979    

DOI:10.1063/1.329842

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The evolution of a tunable dye laser (TDL) pulse in an ultrashort cavity pumped by a monochromatic picosecond light pulse is described using the appropriate laser rate equations. The ultrashort duration of the excitation pulse typically reduces the treatment into one which is directly analogous to the giant pulse model of Wagner and Lengyel, applied previously toQ‐switching dynamics in solid‐state lasers. The spectral properties of the TDL pulse are calculated using an active e´talon model, in which the bandwidth narrowing of the cavity axial modes is governed by the time‐dependent gain derived from the giant pulse model. Theoretical conditions are obtained for achieving operating regimes which correspond to extraction of high pump→TDL conversion efficiencies, to the minimization of TDL pulse durations, or to shot‐to‐shot stabilization of output properties. The feasibility of extracting ∼45% conversion of 531‐nm SHG pulses from the mode‐locked Nd3+: glass oscillator using a 54‐nm rhodamine 6G cavity is confirmed experimentally.

ISSN:0021-8979    

DOI:10.1063/1.329843

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

In an attempt to determine the assignments for the wavelengths observed in the line tunable lithium dimer laser [H. Welling and B. Wellegehausen,LaserSpectroscopyIII(Springer‐Verlag, New York, 1977), p. 365] pumped by the Kr+6471‐A˚ laser, we have examined the corresponding fluorescence spectrum of the7Li2molecules. Unlike the Ar+laser fluorescences which have previously been assigned, the Kr+laser fluorescence of Li2has not been previously studied. Here we present the assigned fluorescence spectrum which consists of two series of theA‐Xsystem (v′ = 9,J′ = 11,v′ = 12,J′ = 60) along with the line frequencies and their calculated absolute radiative transition probabilities. The optically‐pumped laser lines are identified and additional wavelengths are listed which may lase when pumped at 6471 A˚ or at various Ar+laser wavelengths.

ISSN:0021-8979    

DOI:10.1063/1.329844

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Carrier losses in double‐heterostructure lasers are twofold: (i) nonradiative recombination through killers in the bulk of the active region and at all its boundaries (interfaces and surfaces), and (ii) leakage out of the active region. A simple theory shows the following. In the high‐injection regime (p?n) all processes under (i) are directly proportional ton. Consequently their contributions can be lumped together in a single effective nonradiative carrier lifetime &tgr;nr; this &tgr;nris constant (i.e., independent ofn) owing to the constant degree of occupation of all killers in the mentioned regime. On the other hand, the leakage losses (ii) are superlinear inn. This provides a well‐grounded basis for disentangling the contributions of (i) and (ii) in a given sample. Further, a simple method is presented for accurately determining &tgr;nrfrom data of the external quantum efficiency &eegr;extmeasured as a function of currentIin the spontaneous high‐injection regime below the laser threshold. Knowledge of the light‐extraction factor (i.e., the ratio of external and internal quantum efficiencies) is essentially unnecessary with this method. However, optionally it can be determined easily from a slight extension of the method. For illustration the method of determining &tgr;nr, which is also applicable to double‐hetero LED’s, has been applied to some thirty LPE and metal‐organic VPE GaAs‐(Ga,Al)As lasers of widely varying qualities. The values found vary between 0.8 and 55 ns. From the measured values of &tgr;nrit follows that the upper limit for the interface recombination velocity in the best samples is 270 cm/s. For most samples &tgr;nrcannot account for all electrical losses at laser threshold. The superlinear  excess  losses are ascribable to leakage.

ISSN:0021-8979    

DOI:10.1063/1.329845

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The temperature dependence of threshold currents in constricted double‐heterojunction diode lasers with strong lateral mode confinement is found to be significantly milder than for other types of lasers. The threshold‐current relative variations with ambient temperature are typically two to three times less than for other devices of cw‐operation capability. Over the interval 10–70 °C the threshold currents fit the empirical exponential law exp [(T2−T1)/T0] withT0values in the 240–375 °C range in pulsed operation, and in the 200–310 °C range in cw operation. The external differential quantum efficiency and the mode far‐field pattern near threshold are virtually invariant with temperature. The possible causes of high‐T0behavior are analyzed, and a new phenomenon—temperature‐dependent current focusing—is presented to explain the results.

ISSN:0021-8979    

DOI:10.1063/1.329846

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The spatial mode stability of state‐of‐the‐art (AlGa)As oxide stripe cw lasers during aging at 70 °C has been studied. These routinely fabricated devices exhibited reproducible fundamental spatial mode operation and had a median time to failure at 70 °C of 7000 h. While there was wandering of the farfield beam pattern of up to 10° during aging, operation in an essentially fundamental spatial mode continued until very close to the end of life.

ISSN:0021-8979    

DOI:10.1063/1.329847

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An HgBr2/HgBr dissociation laser has been excited in ane‐beam preionized, self‐sustained discharge. Laser output of 100 mJ at 502 and 504 nm has been obtained with an overall efficiency of 0.5%. The steady‐state efficiency for formation of the HgBr (B) state in the Ne/N2/HgBr2discharge is determined to be 4%. An optical gain to loss ratio of ∼ 14 at the laser wavelength is inferred.

ISSN:0021-8979    

DOI:10.1063/1.329848

出版商:AIP    

年代:1981

数据来源: AIP