Temperature dependence of light absorption in water at holmium and thulium laser wavelengths

A simple experimental setup is described that facilitates accurate measurements of the temperature-dependent water absorption coefficient in the mid-infrared spectral region. With this setup, the absorption of holmium and thulium laser radiation in water was quantified to a precision of 0.5%. In the 20-100 degrees C temperature range, a linear decrease of the absorption coefficient with temperature is observed. The slope coefficients amount to -0.104 +/- 0.001 and -0.259 +/- 0.003 l/(K cm) for 2090-nm holmium and 2014-nm thulium radiation, respectively. At both wavelengths, this bleaching reduces the absorption coefficients of water at 100 degrees C by one third when compared with room temperature. A numerical simulation shows that the variable absorption has a noticeable influence on peak temperatures in laser heating of water.     

Temperature dependence of the intensity and phase of reflected light in a liquid-crystal structure with surface plasmons

The results of a theoretical calculation of the temperature dependence of the amplitude coefficient and phase of reflected radiation with wavelength λ=6328 Å in a liquid-crystal structure with surface plasmons are reported for the first time. The computational results could be helpful for developing temperature sensors and optically coupled thermal imagers based on liquid-crystal structures with surface plasmons. Pis’ma Zh. Tekh. Fiz. 23, 11–15 (September 12, 1997)     

Temperature distributions in semi-infinite and finite-thickness media as a result of absorption of laser light

A time-domain method is used to derive simple expressions for temperature distributions within media heated by a moving laser beam with a Gaussian power density profile. Various medium-absorption functions are considered. The solutions are given as single integrals with respect to time of simple functions. The expressions can be applied to multilayer media consisting of layers with different optical (light-absorbing) properties, provided that the layers have similar thermal properties. A number of optical recording examples have been examined in detail, and the results compared with those obtained by use of a more general (fast-Fourier-transform-based) approach.     

Temperature alterations of infrared light absorption by cartilage and cornea under free-electron laser radiation

Like pure water, the water incorporated into cartilage and cornea tissue shows a pronounced dependence of the absorption coefficient on temperature. Alteration of the temperature by radiation with an IR free-electron laser was studied by use of a pulsed photothermal radiometric technique. A computation algorithm was modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The absorption coefficients for several wavelengths within the 2.9- and 6.1-microm water absorption bands have been determined for various laser pulse energies. It is shown that the absorption coefficient for cartilage decreases at temperatures higher than 50 degrees C owing to thermal alterations of water-water and water-biopolymer interactions.     

Temperature distributions in semi-infinite and finite-thickness media as a result of absorption of laser light: erratum

Errors in a paper published earlier [Appl. Opt. 36, 494 (1997)]are corrected. They comprise a corrected definition and line of pseudocode. In the paper "Temperature distributions in semiinfinite and finite-thickness media as a result of absorption of laser light,"(1) two errors appeared and are corrected as follows:     

Temperature dependence of absorption edge in MOCVD grown GaN

We have studied the temperature dependence of absorption edge of GaN thin films grown on sapphire substrate by metal-organic chemical vapor deposition using optical absorption spectroscopy. A shift in absorption edge of about 55 meV has been observed in temperature range 273–343 K. We have proposed a theoretical model to find the energy gap from absorption coefficient using α = α_max + (α_min − α_max)/[1 + exp 2(E − E_g + KT)/KT]. Temperature dependence of band gap has also been studied by finding an appropriate theoretical fit to our data using E_g(T) = E_g(273 K) − (8.8 × 10⁻⁴T²)/(483 + T) + 0.088 (Varshni empirical formula) and E_g(T) = E_g(273 K)−0.231447/[exp(362/T)−1] + 0.082 relations. It has been found that data can be fitted accurately after adding a factor ∼0.08 in above equations. Debye temperature (483 K) and Einstein temperature (362 K) in the respective equations are found mutually in good agreement.     

Temperature influence on light absorption by fresh water and seawater in the visible and near-infrared spectrum

The influence of temperature on light transmission in the spectral range from 400 to 760 nm has been determined in a two-cell instrument constructed especially for this purpose. Light transmission was measured over a 1-m path length in both a photometric and a spectral mode in double-ion-exchanged fresh water and filtered seawater with a salinity of approximately 25%?. For both groups of samples the temperature-dependence coefficient of the absorption was found to be -0.00091 ± 0.00006 m(-1) K(-1) in the range from 400 to 550 nm, in contrast to earlier findings. Reproducible signals could be observed only when the samples were left undisturbed for long periods of time between shifts in temperature. The temperature was scanned in alternating directions between 6 and 30 °C in steps of ± 2 °C. The time for recording a set of data was between 2 and 3 weeks. Finally, the temperature dependences of the absorption spectra were recorded in the range 400 to 760 nm. These measurements are only partially in agreement with earlier measurements.     

Temperature dependence of the Brillouin linewidth in water

In the frequency spectrum of light that is scattered in liquid water there is a central elastically scattered peak that is due mainly to scattering by suspended particles; and, there is a peak on each side of the central peak that is displaced by the Brillouin frequency shift. The Brillouin shift is a direct measure of sound speed. The linewidth of the Brillouin shifted lines is dependent on the bulk and shear viscosity of water as well as its density, thermal conductivity, and specific heat. The linewidth of the Brillouin peaks has been investigated in laboratory experiments over a range 1°C to 35°C. The frequency spectrum of back-scattered laser light was analysed using a scanning Fabry-Perot etalon. A strong dependence of the linewidth of the Brillouin shifted lines on temperature was found. In particular, for low temperatures in the range 10°C down to 1°C the linewidth shows an increase from 750 MHz to 1.4 GHz.     

Traffic and seasonal dependence of the light absorption coefficient in santiago de chile

We have designed and built a compact, low-cost automated system to measure the optical absorption coefficient of air. Because most of the light absorption is due to black carbon, this method is a direct measure of the amount of black carbon in the atmosphere. The equipment was used to measure absorption over a period of one year in a central area of Santiago. Our results show a strong correlation with the daily traffic pattern. The highest value of the absorption coefficient during most of the year occurs during the morning rush hour (0700-0800), and the lowest value either early in the morning (0300-0500) or in the afternoon (1400-1700). The absorption coefficient also shows a strong dependence with the season of the year, with values 10-20 times higher in winter than in summer. The data show that, during most of the year, the amount of black carbon present in the atmosphere is due to traffic. At night, during winter, the high concentration of black carbon is due to the temperature inversion effect.     

Spectral intensity and phase changes of short laser pulses by two-photon absorption

We calculated third order non-linear polarization to estimate the two-photon absorption of non-interacting two-level molecules in the transmission-type degenerate pump–probe geometry. The spectral intensity and the phase changes of the laser pulses when passing through a thin dielectric slab composed of the molecules were considered. We also investigated the effect of the decay rate of the molecules and the chirp of the pulses on their spectral intensity and phase changes.     

Temperature dependence of the heat of crystallization of water

Results of a comparative analysis of thermodynamic relationships are presented, permitting calculation of the temperature dependence of the heat of crystallization of water.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 4, pp. 658–664, October, 1985.     

Temperature dependence of pure CsI: scintillation light yield and decay time

The temperature dependence of the light emission for pure CsI crystals has been measured with photomultipliers, and photodiodes with wavelength shifters from 80–300 K. The light yield at 80 K is N_γ=50,000±5000 photons/MeV. This number was deduced from the number of electron–hole pairs produced in the photodiode, N_eh=39,600±1200. The light yield at room temperature is lower by a factor of 15.8±1.0, giving 3200±400 photons/MeV. Decay times were measured with a photomultiplier. At room temperature two fast decay components were observed with decay times of 6±1 and 28±2 ns. Below 180 K only one component is observed and at 80 K the decay time is 1015±17 ns.     

Pressure dependence of the small-signal gain and saturation intensity of a copper vapor laser

The small-signal gain coefficient and the saturation intensity of a copper vapor laser have been measured for both 510.6- and 578.2-nm transitions through the implementation of a discharge driven oscillator-amplifier configuration. Pressure dependence of the gain and saturation property of the laser has been investigated.     

Diode laser absorption spectroscopy of water vapor in a scramjet combustor

A sensor based on tunable diode laser absorption spectroscopy was constructed for time-resolved temperature and water vapor concentration measurements in a scramjet combustor. The sensor probed two absorption lines near 1390 nm with two time-multiplexed lasers used to measure temperature and water vapor concentration at up to 20 kHz. A demonstration experiment was performed in the supersonic, expanding exhaust region of the combustor, showing the measurement to be repeatable, able to resolve temporal trends during tunnel operation, and sensitive to changes in combustor operating conditions.     

Temperature dependence of the optical absorption spectra of InP/ZnS quantum dots

The optical-absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5–296 K. Using the second-order derivative spectrophotometry technique, the energies of optical transitions at room temperature were found to be E ₁ = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E ₂ = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E ₁(T) has been approximated for the first time in the framework of a linear model and in terms of the Fan’s formula. It is established that the temperature dependence of E ₁ is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.     

Enhanced light absorption of Ag films deposited onto femtosecond laser microstructured silicon

Absorptive properties of silver (Ag) films with the thickness varied from 160 nm to 340 nm deposited onto the surface of femtosecond laser microstructured silicon by vacuum thermal evaporation were measured in a wavelength range of 0.3-16.7 μm. Greatly enhanced light absorption of Ag films has been observed in the whole measured wavelength range. For the same Ag film thickness (268 nm), the light absorption was strongly depended on the height and spacing of the spikes, especially in the region of 1-16.7 μm. The relation between light absorption and thickness of Ag films has also been investigated, it was shown that the light absorption decreases with the increasing thickness of Ag films. The strongly enhanced light absorption in such a wide wavelength range is mainly ascribed to the multiple reflection of light between spikes and surface plasmon excitation of noble metal nano-particles on the spikes surface.