Optical Absorption Values Research Articles

Assessment of diffusion-bonded KTP crystals for efficient, low pulse energy conversion from 1 to 2 μm

Diffusion bonded (DB) walk-off compensated KTP crystals offer an alternative nonlinear medium for efficient 1 to 2 microm conversion within optical parametric oscillators (OPOs) at low pulse energies. Spatial variations in optical absorption and transmission values measured at 2 mum are reported for two DB-KTP crystals. Finally, a comparison is made between the conversion efficiency obtained from a degenerate 1 microm pumped OPO using a single 20 mm KTP crystal and an equivalent length DB-KTP crystal consisting of two bonded 10 mm crystals.

Accelerated protein aggregation induced by macrophage migration inhibitory factor under heat stress conditions

Kinetics of thermal aggregation of model protein substrates (glycogen phosphorylase b from rabbit skeletal muscle and yeast alcohol dehydrogenase) were investigated under heat stress conditions (41-48 degrees C) in the presence of macrophage migration inhibitory factor (MIF), a heat-stable hydrophobic protein (12.5 kD). Anti-chaperone MIF activity found by turbidimetry manifests itself in significantly accelerated protein aggregation and increased limiting value of apparent optical absorption at 360 nm and t --> infinity in the sub-stoichiometric range of MIF concentrations. The aggregation kinetics is shown to have cooperative character. Possible reversibility of aggregation after removal of denaturing conditions was demonstrated using alcohol dehydrogenase aggregation at a temperature close to the physiological level (41.5 degrees C). This reversibility is caused by solubility of aggregates and stabilization of oligomeric structure of the substrate as a result of MIF binding to the partially denatured protein. The data suggest that in spite of distinct anti-chaperone effect, the chaperone-like activity of MIF can be observed in the case of heat stress removal and restoration of the system to normal conditions.

Hydrogenated amorphous and microcrystalline GaAs films prepared by radio-frequency magnetron sputtering

We report on the optical absorption, adhesion, and microstructure of radio-frequency magnetron sputtered films of hydrogenated amorphous and microcrystalline GaAs films for the 1 to 25 μm infrared wavelength range. Sputtering parameters which were varied include sputtering power, temperature and pressure, and hydrogen sputtering-gas concentration. Transmission electron microscopy results show a sharp transition from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous matrix at a substrate-holder temperature of 34±2 °C. By optimizing the sputtering parameters, the optical-absorption coefficient can be decreased below 100 cm−1 for wavelengths greater than about 1.25 μm. These results represent the lowest reported values of optical absorption for sputtered films of GaAs directly measured by spectrophotometry for the near-infrared wavelength region.

NIR Absorption of Nb4+ Polarons in Reduced SBN Crystals

A stable broad absorption band around 0.72 eV, assigned to the absorption of Nb4+ polarons, is observed in pure SBN, SBN:Cr or SBN:Ce crystals after previous reduction treatment at T < 800 °C in Ar, vacuum or H2. The absorption spectrum of Nb4+ polarons in reduced SBN crystals shows a considerable dichroism, which exists even far above room temperature. The peak position and the integrated absorption of Nb4+ polarons are measured as a function of temperature. The maximum of the Nb4+ polaron absorption shifts to higher energies with decreasing temperature. A comparison of optical absorption and recent literature values [1] of the magnetic susceptibility and therefore concentration of polarons yields values of the optical oscillator strength estimated to be f ≈︂ (5 ± 0.6) × 102.

The ratio of aerosol optical absorption coefficients to sulfur concentrations, as an indicator of smoke from forest fires when sampling in polar regions

Analyses of aerosol composition data from seven National Park Service locations in Alaska were performed. All of the sampling sites in Alaska experience aerosol pollution from long distance and regional sources. One of the most important regional sources of particles in the area is wood smoke from forest fires. The Denali National Park aerosol data and the corresponding meteorological data made it possible to identify samples of background (long-range-transported) aerosol, which are likely to be without contamination from local and regional sources. Background values of optical absorption (BABS) and sulfur concentration for this site are well correlated and in ranges of 2 × 10 −7−50 × 10 −7 m −1 and 10–350 ng m −3, respectively. Positive matrix factorization method was used for obtaining information about possible sources of aerosol in the remote locations. Seasonal variations with maxima during the winter-spring season and minima in summer were observed for the sulfur concentration but not for BABS. Seasonal variations were always higher for the more northerly locations. The influence of emissions from regional sources on the BABS values was higher than for sulfur concentrations. The ratios of optical absorption coefficient to sulfur concentration were used to characterize the relative influence of regional pollution sources on the measured particle compositions.

Calculation of the Z 1-center absorption bands

The optical absorption of the Z 1-band in alkali halides was studied using point-ion and ion-size correction models. Several alkali halides with Ca 2+ impurities were investigated. For the calculations, the Gourary and Adrian [Gourary B. S. and Adrian F. J., Solid State Physics, Vol. X. Academic Press, New York (1960)] wave functions as well as the Gaussian wave functions were used. Some discrepancies in the energy values with the Weber and Dick [Dick B. G., Phys. Stat. Sol. 28, 223 (1968)] paper were found using the Gourary and Adrian wave functions. Good agreement with the experimental optical absorption values was found for the xȳ Gaussian wave functions, using the point-ion model, and for the z Gaussian wave functions using the ion-size correction model, for the excited state, and the Gaussian wave functionals for the corresponding ground states. We obtained the energy functionals for the type I, II, III and Gaussian wave functions. With the point-ion method the difference between theoretical and experimental values is smaller than 11 % for the ion-size-correction method the difference is less than 17%.

Properties and Effects of Laser-Induced Plasma During Evaporative Deposition of Thin Films

ABSTRACTThe properties of plasmas generated by the interaction of a pulsed CO2 laser with several solid evaporation targets were studied and the films deposited from such plasmas were characterized. A large flux (˜ 1014/cm2/s) of ions at high velocities (2 − 10 × 106 cm/s) was measured in these plasmas. ZrO2 thin films deposited by laser-assisted evaporation on room temperature substrates had crystalline-oriented structures. Low optical absorption and high refractive index values (2.15 at 632.8 nm) indicated the stoichiometric and dense nature of these films.

Effect of active layer thickness on differential quantum efficiency of 1.55 μm InGaAsP buried crescent injection lasers

Comprehensive measurements of the differential quantum efficiency (ηd ) dependence on the active layer thickness (d) for 1.55 μm InGaAsP buried crescent (BC) injection lasers are presented. The results show that ηd increases rapidly as d decreases. The strong d dependence of ηd in 1.55 μm BC lasers suggests that a large value of optical absorption in the active region is one of the dominant mechanisms which determines the ηd of these InGaAsP lasers. The likely cause for large absorption in the active region is intervalence band absorption (IBA). Thus, by reducing the active layer thickness and hence, the effect of IBA, we have obtained 1.55 μm BC lasers which exhibit threshold currents as low as 9 mA at 25 °C, ηd over 45%, and high-temperature operation up to 100 °C.

DUST IN THE NUCLEI OF THE SEYFERT GALAXIES MARKARIAN 231 AND NGC 4151.

ABSTRACT Observations carried out with a 8-13 micron grating-spectrometer of Mrk 231 and NGC 4151 are reported. The Mrk 231 data can be fitted to various thermal dust emission models or a single power law, with dust extinction. In all the model fits, except for that of graphite and silicon carbide grain emission, a component of silicate absorption of optical depth of not more than 0.7 is required. Confirming published work, the absorption being at the redshift of the low-redshift absorption-line system is ruled out. The high values of silicate optical depth absorption do not give ratios to the galaxy's visual extinction which are comparable to those of galactic H II regions. Weak evidence for a 10-micron absorption feature in NGC 4151 is also reported. This is somewhat contrary to expectation, since the visual extinction of NGC 4151 is lower than that of Mrk 231, and since there is evidence to support a nonthermal rather than thermal dust origin for the infrared continuum emission.

Density of the gap states in undoped and doped glow discharge a-Si:H

The density of the gap states in undoped and phosphorus and antimony doped a-Si:H has been determined from the absorption coefficient measurement. A constant photocurrent method was used to determine the value of optical absorption in the low absorption region. A quantitative model has been suggested to explain all experimental data. The model is based on a Gaussian shaped maximum, connected with the dangling bond, within the exponential band tails just below the middle of the gap. Moderate and strong coping rises the concentration of dangling bonds.

Materials for magneto-optic modulators

A review of the current status of magneto-optic modulator materials is presented with emphasis on operation at the Nd3+:YAG wavelength of 1.064 μm. Because the iron garnets are “cubic”, exhibit small values of linear magnetic birefringence, and offer great flexibility in ion substitutions and some flexibility in optical absorption values, these materials provide clear advantages over any other known class of magnetic compounds. Recent work has also shown that Faraday rotati ons in the iron garnets can be remarkably enhanced by Bi3+ and/or Pr3+ substitutions. The physical origin of this enhancement is briefly outlined in terms of the iron garnet energy level structure. An important problem that has not as yet been completely resolved is the question of intrinsic optical absorption at 1.064 μm. Evidence is presented showing that optical losses in the 1–4 cm−1 (0.43–1.7 db/mm) range should be achievable in praseodymium-substituted gadolinium iron garnet, but thus far the lowest observed absorption coefficient is 5.9 cm−1 = 2.6 db/mm. In the case of bismuth-substituted garnets the lowest observed absorption at 1.064 μm is 13 cm−1 = 5.6 db/mm. The importance of impurities, nonstoichiometry, and Pb incorporation from the flux is emphasized. Finally, we point out that other material properties such as magnetocrystalline anisotropy, ferromagnetic resonance frequency and linewidth, and values of 4πMS should be included in any complete materials evaluation.

The optical properties of lead in the energy range 0·6-6 ev

Abstract An ellipsometer used with the sample enclosed in an ultra-high vacuum chamber is described. It permits the determination of optical constants of evaporated films in vacua ∼5 × 10−10 torr. Lead films have been studied in the energy range 0·6 to 6 ev. The absolute values of optical absorption are considerably higher than previous published values. Since it is shown that exposure to air causes a large decrease in size it is considered that the high values are characteristic of clean lead. The absorption spectrum is discussed in terms of Loucks’ band structure calculation. Assignments of interband transitions are made and reasonable agreement between experiment and band calculation found.