Spectral Half-width Research Articles

Vapor-phase growth of (In,Ga)(As,P) quaternary alloys

Crystal growth techniques for the metal chloride-hydride vapor-phase epitaxy of InGaAsP alloys are described. The growth conditions and gas flows for alloys with energy bandgap wavelengths in the range of 1.0-1.7 \mu m are specified. Calibrations for n- and p-type doping and relationships between the photoluminescence spectral half-width and doping level are also presented. Mobility values as high as 4500 cm2/V . s (300 K) and electron diffusion lengths as long as 1.75 μm have been measured in InGaAsP alloys. The growth of alloys over vee, dovetail, and circularly defined regions in InP substrates is also discussed.

Spectral Half-Width of Spontaneous Emission of GaInAsP Lattice-Matched to InP

Spectral Half-Width of Spontaneous Emission of GaInAsP Lattice-Matched to InP

Observations of the diffuse interstellar EUV radiation field

Results are reported for observations and a preliminary theoretical analysis of the diffuse interstellar EUV radiation field exhibiting positive measurable fluxes in the wavelength range from 912 to 1150 A. The observations were made with the UV spectrometers on the two Voyager spacecraft, and a spectral half-width of 30 A was obtained. The procedures used in the analysis are described in detail, particularly those relating to the elimination of thermal and cosmic-ray noise, internal instrumental scattering from bright lines, and possible contributions from direct starlight. Measurements in several directions reveal diffuse intensities at 975 A ranging from a maximum of about 10 to the -7th erg/sq cm per (sec sr A) near the galactic plane to an upper limit of 10 to the -8th erg/sq cm per (sec sr A). A comparison of the present measurements with various theoretical predictions and previous measurements indicates reasonable agreement with some theoretical predictions of the interstellar EUV intensity.

Singe-mode cw operation of ’’double-dovetail’’ constricted DH (AlGa)As diode lasers

Constricted double-heterojunction (CDH) lasers have been prepared in a double-dovetail channel structure, which consistently provides cw fundamental-mode operation. Oscillation in both single lateral and single longitudinal modes (spectral halfwidth <0.09 Å) is obtained at drive currents 50–100% above threshold and to cw power levels as high as 12 mW. ’’Kinkless’’ power-current curves at 20 and 70°C have been obtained from all lasers prepared to date to power levels close to that at which degradation occurs (∼30 mW cw at 20 °C for a 3–4-μm-wide lasing region). Threshold currents of 55–75 mA and external differential quantum efficiencies (one facet) of 15–17% are obtained from 120–150-μm-long diodes with a reflector on one facet. Threshold current ratios as low as 1.26 have been measured between 20 and 70 °C.

Spectrally narrow pulsed dye laser without beam expander

We have developed a simplified version of the side-pumped pulsed dye laser which has a spectral halfwidth of 1.25 GHz and a peak power of 10 kW at 600 nm. The basic laser consists of only four components (output mirror, dye cell, diffraction grating, and tuning mirror) and is exceptionally easy to align. Since the beam expander has been eliminated, the laser cavity can be made quite compact. Under the condition of reduced gain, the laser has been operated in a single mode.

GaAs/GaAlAs diode lasers with angled pumping stripes

Operation of DH GaAs/GaAlAs stripe contact lasers with stripes oriented nonorthogonally to the cleaved end facets of the laser is described. Such lasers, with misalignment angles of \sim2\deg , do not exhibit kinking behavior to power levels greater than 90 mW/facet, and do not exhibit relaxation oscillations under pulsed operation. Data showing the dependence of laser wavelength, spectral half-width, transverse mode structure, facet reflectivity, and output beam angle on both stripe angle and pump current level are also presented.

InGaAsP/InP d.h. l.e.d.s for fibre-optical communications

InGaAsP l.e.d.s emitting at 1.24 μm are fabricated. Their characteristics at 100 mA are as follows: output power coupled into the fibre of 77 μW, a spectral halfwidth of 0.1 μm and a cutoff frequency of 70 MHz. The cutoff frequencies are proportional to the square root of the bias current. The recombination coefficient is estimated to be 5 × 10−10cm3/s

Efficiency of thin-film acoustooptic light deflectors for a Gaussian guided optical beam

We have investigated deflection efficiency of thin-film acoustooptic light deflectors for a narrow guided optical beam (GOB). Dependences of the maximum deflection efficiency eta(max) on spreading angle (deltatheta) of such a GOB and that (deltaPhi) of a surface acoustic wave were revealed experimentally and theoretically for He-Ne and GaAlAs double heterostructure (DH) lasers. eta(max) is drastically reduced when deltatheta increases to deltaPhi; and eta(max) increases with increasing deltaPhi for fixed deltatheta. Even for a DH laser having a spectral halfwidth of about 63 A, the spectral distribution scarcely affects eta(max) in this deflector. Some restrictions are pointed out in designing the deflector with higher eta(max) for a narrow GOB.

The Detection of Hg(63P1 and 63P0) Atoms by an Atomic Absorption Method and Their Quenching Cross Sections

Abstract The absorption intensities of the 435.8- and 404.7-nm lines by Hg(63P1 and 63P0) atoms were calculated taking into account the hyperfine structure under the assumption of a Doppler spectral line shape. The calculated values were tested by comparison with experimental absorption of the line in an Ar+N2+Hg mixture illuminated by 253.7-nm radiation. This procedure led to the conclusion that the ratio of the spectral half-width of the 404.7-nm line from a low-pressure Hg lamp to that of the Hg(63P0) absorption line should be 2.25±0.25 instead of the value of 5 determined in the previous experiment. On the basis of this value, the quenching cross sections of the excited Hg atoms reported in the previous paper were revised. The corrections are generally less than 20%, so that it is not necessary to change the previous conclusions.

Depolarized Rayleigh scattering studies of molecular motion of 1,3,4-[D 2] thiadiazole

Depolarized Rayleigh scattering spectra have been measured using a Fabry-Pérot interferometer for 1,3,4-[D 2] thiadiazole at temperatures between 20 and 92.5°C, covering a large portion of the liquid and supercooled liquid regions. From the spectral halfwidth measurements, the Rayleigh relaxation times, τ Ray, have been obtained. A semilog plot of τ Ray versus T −1 shows that the data fit well to an Arrhenius equation, with activation energy equal to 2.4 kcal/mole. The relation of τ Ray to pair orientation correlations is discussed.

Silicon-doped gallium arsenide antimonide electroluminescent diodes emitting to 1.06 μm

We report efficient room-temperature emission to 1.06 μm from silicon-doped gallium arsenide antimonide electroluminescent diodes fabricated in GaAs1−xSbx layers grown on GaAs substrates in a single-step LPE growth from melts containing from 0.1 to 1.1 at.% Si. The spectral half-width of the emission is 42.5 nm at 0.96 μm and 79 nm at 1.06 μm.

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF 2 underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.

Dependence of fluorescence characteristics on the bandwidth of exciting and observed light

A method is described for determination of the quasimonochromatic (elementary) fluorescence characteristics (absorption, fluorescence and polarization spectra, and the wavelength-dependent relative quantum yield of fluorescence) from experiments with beams of non-zero spectral half-width. The error of the approximate solution of the linear integral equation of first order is estimated. In certain spectrum regions the differences between the elementary and measured characteristics of fluorescein and trypaflavine in water and glycerol are much higher than the experimental error.

Properties of high-efficiency zinc-diffused Ga1-xAlxAs light-emitting diodes

The external quantum efficiency of zinc-diffused hemispherically-shaped Ga1-xAlxAs light-emitting diodes has been investigated as a function of temperature, peak emission energy, and current. External quantum efficiencies as high as 13.5% and 52% have been achieved at 296°K and 77°K, respectively. An analysis of the temperature dependence of the spectral characteristics (emission spectral shape, peak emission energy, and spectral half-width) shows that the improved efficiencies at room temperature result from reduced internal bulk absorption due to a composition gradient in the emitter. Values as small as 3.4 have been observed for the ratio of the 77°K efficiency to the 296°K efficiency. The decrease of the external quantum efficiency at high peak emission energies (short wavelengths) agreed with the decrease theoretically predicted from the composition dependence of the direct and indirect energy gaps of Ga1-xAlxAs. A decrease of external quantum efficiency at low currents was shown to be due to a nonradiative parallel component of current.

Preferential etching of ion bombarded GaAs

Abstract Abrupt changes in the near-band-edge luminescence of n-type undoped GaAs after implantation with 400 keV Zn ions and vacuum annealing at 580°C are reported. The good agreement of the spectral position, half-width and temperature dependence of the emission obtained after implantation and annealing with that of melt-doped GaAs: Zn indicates that implanted Zn ions have been incorporated at Ga lattice sites. The larger number of Zn substitutions obtained when bombardment is made on the Ga face than for an equivalent fluence on the As face demonstrates the existence of a polar implant effect.

Spectroscopic Determination of Quenching Cross-Sections of Excited Mercury Atoms (63P1, 63P0) in Molecular Collisions

Abstract The concentrations of Hg(63P1) and (63P0) atoms, [Hg1*] and [Hg0*], were determined from the absorptions of 4358 and 4047 Å lines in the Ar-diluted mercury vapor in the presence of several quenching molecules, under the radiation of 2537 Å emission. An apparent absorption intensity was not proportional to [Hg1*] or [Hg0*], and was sensitive to the ratio of the spectral half-width of the light source to that of the absorption line. Therefore, a method to correct an absorption intensity was proposed. The relation of [Hg1*] to [Q], a concentration of quenching molecules, is explained well by the Stern-Volmer equation. The value of [Hg0*] increases with [Q] until it reaches a maximum at a certain value of [Q], and a further increase of [Q] results in a decrease of [Hg0*]. These findings are explained well by the following mechanism: (1) Hg+hν→Hg1*, (2) Hg1*→Hg+hν, (3) Hg1*+Q→Hg+Q, (4) Hg1*+Q→Hg0*+Q, (5) Hg0*+Q→Hg+Q, (6) Hg0*→Hg (by collisions with a wall). The respective values of cross-sections (σ2) of N2, CO, and NO for process (3) are ≤0.03, 0.60, and 20 Å2, and those for process (4) are 0.36, 2.1 and 5 Å2, and those for process (5) are ≤3.6×10−4, 0.15 and 8.0 Å2.

Electroluminescence Characteristics and Efficiency of GaAs:Si Diodes

The peak wavelength, spectral half-width, and efficiency of liquid-phase epitaxial GaAs:Si diodes were determined as a function of silicon concentration in the melt. The peak of the emission spectrum could be shifted from about 9200 to 10 000 Å by varying the silicon concentration. For all wavelengths investigated, uncoated diodes with 6% efficiency could be made, with some going as high as 10%. External room-temperature dc efficiencies up to 32% were measured on diodes provided with high-index glass domes. The spectral half-width was found to increase with silicon concentration, and was especially large for growth on the 111B plane. The internal absorption loss was found to be significant for all peak wavelengths. These findings are discussed in the light of current models of recombination processes in heavily doped semiconductors.

Some characteristics of dye lasers with nitrogen laser pulse excitation

Results from experiments in which the ultraviolet pulses from a nitrogen laser are used to obtain laser action from organic dyes are described. The dyes include three in the xanthene group (rhodamine 6G, B, and sodium fluorescein) and two coumarins, 7-diethylamino-4-methylcoumarin and 7-N-dimethylamino-4, 6-dimethylcoumarin) in ethanol solvent. With these dyes, laser power is available over the entire visible range from 4200 to 6300 A when used with a rotatabie diffraction grating. The range of tunability of one of the dyes was extended to ∼ 1000 A by appropriate acidification. The spectral halfwidth of the light varied between 7 and 15 A over the range of tunability. Maximum repetition rates of 100 pps were obtained. Maximum power efficiency of ∼ 25% was found for rhodamine 6G. Overall output pulse shapes were found to be in agreement with the theory of Sorokinet al. Output pulse widths varied from ∼ 1 to 7 nsec. Other dyes which we have found to lase by this method of excitation include acridone, chloro-aluminium pthalocyanine and 4-methylumbelliferone. However, these dyes will not be discussed further in the text.

Reflectivity of Mars, 2550-3300 Å

view Abstract Citations (8) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Reflectivity of Mars, 2550-3300 Å Broadfoot, L. ; Wallace, L. Abstract Mars was observed near opposition with a rocket-borne telescope-spectrometer. The 2550-3500 A region of the Martian spectrum was recorded wfth a spectral half-width of 3 A. This spectrum resembles that of the Sun very accurately, and no narrow absorption features were found. The geometric albedo of the planet does not show the Rayleigh type of enhancement toward shorter wavelengths which is predicted by a reflecting-layer model of the atmosphere. Agreement with the observed albedo can be obtained by postulating a slight decrease in ground albedo toward the shorter wavelengths, a small amount of ozone in the atmosphere, or a combination of both. An abundance of 2 X 10- cm-atm of O3 or greater would have been detected. Publication: The Astrophysical Journal Pub Date: July 1970 DOI: 10.1086/150532 Bibcode: 1970ApJ...161..303B full text sources ADS |

Spectral Broadening of Europium Ions in Glass

The fluorescence and absorption spectra of trivalent europium ions in glass were measured and compared with the spectra of single crystals of ${\mathrm{Gd}}_{2}$${\mathrm{O}}_{3}$: Eu. It was determined that there is a great similarity between the optical properties of the rare-earth glasses and rare-earth sesquioxide crystals. The spectral studies showed that the europium ions locate in two, and possibly three, average environment sites in glass, mirroring the three sites in which the ion locates in the monoclinical form of the sesquioxide. The primary broadening mechanism was found to be inhomogeneous as determined by the temperature independence of the spectral half width and peak wavelength in the range from 4 to 300\ifmmode^\circ\else\textdegree\fi{}K. This inhomogeneous broadening arises from the heterogeneity of the ion environment in glass.