Wavelength-dependent Emission Research Articles

Observation of cavity effect on spontaneous emission lifetime in AlGaAs quantum microcavities using continuous tuning of emission wavelength

Cavity effect on spontaneous emission lifetime has been observed through the continuous tuning of the emission wavelength by quantum confined Stark effect in AlGaAs Fabry–Perot microcavities. The obtained emission wavelength dependence of the exciton lifetime shows that the lifetime increases with the emission wavelength, specifically indicating a sharp increase at the cavity resonant wavelength. This behavior agrees well with the theoretical prediction based on the theoretical model of G. Björk, S. Machida, Y. Yamamoto, and K. Igeta [Phys. Rev. A 44, 669 (1991)]. Furthermore, we have also investigated the emission wavelength dependence of the transfer efficiency and obtained good agreement with the theory.

Intramolecular dynamics in the environment of the single tryptophan residue in staphylococcal nuclease

The dipole relaxational dynamics in the environment of a single tryptophan residue Trp-140 in staphylococcal nuclease was studied by time-resolved (multi-frequency phase-modulation) spectroscopy and selective red-edge excitation. The long-wavelength position of the fluorescence spectrum (at 343 nm) and the absence of red-edge excitation effects at 0 and 20°C indicate that this residue is surrounded by very mobile protein groups which relax on the subnanosecond time scale. For these temperatures (0-20°C) the steady-state emission spectra did not show the excitation-wavelength dependent shifts (red-edge effects) for excitation wavelengths from 295 to 308 nm; however, the anisotropy decay rate is slow (tens of nanoseconds). This suggests that the spectral relaxation is due to mobility of the surrounding groups rather than the motion of the tryptophan itself. The motions of the tryptophan surrounding are substantially retarded at reduced temperatures in viscous solvent (60% glycerol). The temperature dependence of the difference in position of fluorescence spectra at excitation wavelengths 295 and 305 nm demonstrate the existence of red-edge effect at sub-zero temperatures, reaching a maximum value at −50°C, where the steady-state emission spectrum is shifted to 332 nm. The excitation and emission wavelength dependence of multi-frequency phase-modulation data at the half-transition point (−40°C) demonstrates the existence of the nanosecond dipolar relaxations. At −40°C the time-dependent spectral shift is close to monoexponential with the relaxation time of 1.4 ns.

High-power broadband singlemode Pr 3+ - doped fibre superfluorescence light source

A broadband Pr3+-doped silica-based fibre superfluorescence light source at 1049 nm is demonstrated. For ~4 m length of Pr3+-doped fibre, the authors obtain an output power of 60 mW and a linewidth of ~20 nm at a pump power of 190mW. The dependence of the peak emission wavelength on the wavelength of the pump is investigated. The intensity weighted average wavelength is stable with only a small fluctuation of ±0.2 nm for different pump powers.

A combined heat-transfer analysis of a single-fiber CVD reactor

A combined-conjugated heat-transfer and fluid-flow analysis is presented for coating fibers by CVD in a vertical cylindrical quartz reactor. The numerical model focuses on radiation and natural convection. Three case studies are performed, and the wall temperature predictions are compared to experimental measurements. In the first case, the flowing gas is hydrogen, and conduction is more important than both radiation and convection, in which case measured and predicted wall temperatures agree excellently. In the second, hydrogen is replaced by argon, thus making radiation heat transfer more important than the previous situation. Three radiation models with increasing degrees of sophistication are compared: an approximate nongray model (no wavelength dependence of emissivity), an approximate semigray model, and a rigorous semigray model with view factor calculations. Comparison with experiments suggest that a semigray radiative analysis is needed for correct determination of wall temperatures. The third involves argon at a lower flow rate, where natural convection effects are more pronounced. Checking the validity of the Boussinesq approximation by incorporating the explicit dependence of density on temperature in the model shows a slight difference between the velocity fields predicted using the Boussinesq approximation and those obtained using the explicit dependence of density on temperature. However, there is negligible difference between the temperature fields predicted in the two cases.

Fluorophore environments in membrane-bound probes: a red edge excitation shift study.

A shift in the wavelength of maximum fluorescence emission toward higher wavelengths, caused by a shift in the excitation wavelength toward the red edge of the absorption band, is termed the Red Edge Excitation Shift (REES). This effect is mostly observed with polar fluorophores in motionally restricted media such as very viscous solutions or condensed phases. In this paper, we report the red edge excitation shift of a membrane-bound phospholipid molecule whose headgroup is covalently labeled with a 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) moiety. When incorporated into model membranes of dioleoyl-sn-glycero-3-phosphocholine (DOPC), the NBD-labeled phospholipid (NBD-PE), exhibits a red edge excitation shift of 10 nm. In addition, fluorescence polarization of NBD-PE in membranes shows both excitation and emission wavelength dependence. The nonpolar membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH) does not show red edge excitation shift in model membranes. The lifetime of NBD-PE in DOPC vesicles was found to be dependent on both excitation and emission wavelengths. These wavelength-dependent lifetimes are correlated to the reorientation of solvent dipoles around the excited-state dipole of the NBD moiety in the membrane. The magnitude of the red shift in the emission maximum for NBD-PE was found to be independent of temperature, between 12 and 54 degrees C, and of the physical state (gel or fluid) of the membrane. Taken together, these observations are indicative of the motional restriction experienced by this fluorophore in the membrane. Red edge excitation shift promises to be a powerful tool in probing membrane organization and dynamics.

Optical properties of a Cr3+-doped fluorophosphate glass investigated by steady state and time-resolved laser spectroscopy

The optical properties of trivalent-chromium-doped fluorophosphate glass (21.74 Al(PO3)3-57.8 BaF2-19.96 AlF3 (wt.%)) have been investigated in the 4.2-300 K temperature range using steady state and time-resolved laser spectroscopy. The luminescence of Cr3+ shows a strong thermal quenching which can be analysed in terms of the quantum mechanical single-configurational coordinate model. In order to establish a correlation between the glass matrix composition and the spectral and temperature behaviour of the Cr3+ photoluminescence, detailed time-resolved measurements have been performed. When compared with fluoride glasses, the results attained for the emission wavelength dependence of the lifetimes and excitation spectra show an enhancement of the site-dependent effects.

Far-infrared observations of NGC 4945 and the Circinus galaxy

view Abstract Citations (20) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Infrared Observations of NGC 4945 and the Circinus Galaxy Ghosh, S. K. ; Bisht, R. S. ; Iyengar, K. V. K. ; Rengarajan, T. N. ; Tandon, S. N. ; Verma, R. P. Abstract Results of observations of NGC 4945 and the Circinus galaxy carried out with a 1 m balloon-borne far-infrared telescope are reported. While only an upper limit (5 σ) of 150 Jy for the 150 micron flux density is obtained for Circinus, the central region NGC 4945 has been mapped in two bands with effective wavelengths of ~58 and ~150 microns. Pointed observations of IRAS, using survey detectors, have been deconvolved to get higher angular resolution intensity maps at 12, 25, 60, and 100 microns, respectively, for both of these galaxies. In addition, using the maps in the neighboring bands (12/25, 25/60, and 60/100), spatial distributions of the dust temperature and the optical depth have also been obtained. In NGC 4945, the nucleus has been found to be cooler than its immediate surroundings. Deconvolved intensity maps have also been obtained from the IRAS Chopped Photometric Channel data at 50 and 100 microns. Whereas both these galaxies show a prominent central source, only NGC 4945 shows extended disk emission in all bands. The central source in both the galaxies is found to be somewhat more extended than a point source at wavelengths 50 microns or greater, the resulting deconvolved size being ~40". Symmetric spiral arm like features of NGC 4945 seen in the far-infrared IRAS maps have counterparts in radio continuum, H I and ^12^CO maps. The 150 microns observations for NGC 4945, for ɛ is proportional to λ^-1^, indicate presence of dust cooler than that implied by the IRAS observations. The 150 micron upper limit for the Circinus galaxy implies a steeper wavelength dependence of dust emissivity (ɛ is proportional to λ^-2^ or steeper) than is the case for NGC 4945. Publication: The Astrophysical Journal Pub Date: May 1992 DOI: 10.1086/171328 Bibcode: 1992ApJ...391..111G Keywords: Far Infrared Radiation; Galactic Nuclei; Infrared Astronomy; Spiral Galaxies; Astronomical Photometry; Balloon-Borne Instruments; Cosmic Dust; Infrared Astronomy Satellite; Infrared Telescopes; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4945; GALAXIES: INDIVIDUAL NAME: CIRCINUS; INFRARED: GALAXIES full text sources ADS | data products SIMBAD (3) NED (2)

Anatomy of 1986 Augustine volcano eruptions as recorded by multispectral image processing of digital AVHRR weather satellite data

Eighteen digital AVHRR (advanced very high resolution radiometer) data sets from NOAA-6 and NOAA-9 polar-orbiting satellites recorded between 27 March and 7 April 1986 depict the eruptive activity of Augustine volcano, located 280 km SW of Anchorage, Alaska. The synoptic view (resolution of either 1.1 or 4.4 km), frequent coverage (often twice a day), and multispectral coverage (five bands: 0.58–0.68; 0.72–1.1; 3.55–3.93; 10.5–11.3; and 11.5–12.5 μm) makes the AVHRR broadly applicable to analyzing explosive eruption clouds. The small scale of the Augustine activity (column heights of 2–13 km and eruption rates of 2x106–8x107 metric tonnes/day) facilitated intensive multispectral study because the plumes generally covered areas within the 550x550 km area of one easily manipulated image field. Hourly ground weather data and twice-daily radiosonde measurements from stations surrounding the volcano plus numerous volcanological observations were made throughout the eruption, providing important ground truth with which to calibrate the satellite data. The total erupted volume is estimated to be at least 0.102 km3. The pattern of changing eruption rates determined by satellite observations generally correlate with more detailed estimates of explosion magnitudes. Multispectral processing techniques were used to distinguish eruption clouds from meteorological clouds. Variable weather during the Augustine eruption offered an opportunity to test various trial algorithms. A ratio between thermal IR channels four and five, served to delineate the ashbearing eruption plumes from ordinary clouds. Future work is needed to determine whether the successful multispectral discrimination is caused by wavelength-dependent variable emission of silicate ash or reflects a spectral role of sulfuric acid aerosol in the plume.

A laser heating system that stabilizes and controls the temperature: Diamond anvil cell applications

A laser heating system is described for use with diamond anvil high pressure cells that directly senses and stabilizes visible thermal radiation emitted by hot samples. This technique stabilizes sample temperatures better than other methods and allows superior temperature control. Calibration of the system was checked by measuring the melting temperatures of five metals at ambient pressure. Assuming literature values for spectral emissivity, the calibration was found to be accurate to 3.3% (based upon one standard deviation of the percentage error from published melting temperatures). Performance of the laser heating system was verified by heating iron foil at 13 GPa. With the sample intensity unstabilized, mean temperature was 3003 K with a standard deviation of 144 K, while with it stabilized, mean temperature was 3051 K with a standard deviation of 8 K. For a given wavelength-dependent emissivity, the difference between the actual temperature and the greybody temperature increases as the temperature increases. Therefore, to accurately determine temperatures at the high temperatures applicable to solid Earth geophysics (1500–6000 K), wavelength-dependent emissivity cannot be ignored.

A new method for analyzing IRAS data to determine the dust temperature distribution

In attempting to analyze the four-band IRAS images of interstellar dust emission, it is found that an inversion theorem recently developed by Chen (1990) enables distribution of the dust to be determined as a function of temperature and thus the total dust column density, for each line of sight. The method and its application to a hypothetical IRAS data set created by assuming a power-law dust temperature distribution, which is characteristic of the actual IRAS data for the Monoceros R2 cloud, are reported. To use the method, the wavelength dependence of the dust emissivity is assumed and a simple function is fitted to the four intensity-wavelength data points. The method is shown to be very successful at retrieving the dust temperature distribution in this case and is expected to have wide applicability to astronomical problems of this type.

Temperature dependence of emission wavelength in 1.3μm GaInAsP/InP GRIN SCH MQW laser diodes grown by MOCVD

1.3 mu m GaInAsP/InP GRIN SCH MQW laser diodes grown by low-pressure MOCVD were operated without mode hopping in a single longitudinal mode over a wide temperature range Delta T (5-45 degrees C). The temperature coefficient of the wavelength in this range was 0.8 AA deg-1, which was as small as that of the distributed feedback laser. At the extremes of this temperature range mode hopping occurred. The wavelength did not shift into the nearest neighbouring mode but into one which was separated by several mode spacings. An interference between the fundamental and higher-order transverse modes might be the underlying mechanism.

ChemInform Abstract: Subpicosecond Fluorescence Anisotropy Studies of Tryptophan in Water.

Ultraviolet fluorescence upconversion optical gating has been used to measure the excitation and emission wavelength dependence of the fluorescence depolarization of tryptophan in water with subpicosecond resolution. An initial anisotropy of 0.4 is observed for the first time. The short time decay behavior is found to be complicated by non-rotational contributions to the anisotropy decay arising from the interaction of the two low-lying 'L, and 'Lb excited states. The time constant for 'L, to 'La internal conversion is found to be 1.6 f 0.2 ps. A generalized version of the level kinetics model of Cross et aLZ9 is found to adequately describe the fluorescence anisotropy decay dependence on excitation and emission wavelength. The anisotropy data are interpreted in terms of a model for tryptophan fluorescence depolarization that includes the effects of vibronic coupling and vibrational relaxation. Our results indicate that the fluorescence anisotropy will be an ambiguous method of studying protein motion for times less than 5-10 ps.

Subpicosecond fluorescence anisotropy studies of tryptophan in water

Ultraviolet fluorescence upconversion optical gating has been used to measure the excitation and emission wavelength dependence of the fluorescence depolarization of tryptophan in water with subpicosecond resolution. An initial anisotropy of 0.4 is observed for the first time. The short time decay behavior is found to be complicated by non-rotational contributions to the anisotropy decay arising from the interaction of the two low-lying 'L, and 'Lb excited states. The time constant for 'L, to 'La internal conversion is found to be 1.6 f 0.2 ps. A generalized version of the level kinetics model of Cross et aLZ9 is found to adequately describe the fluorescence anisotropy decay dependence on excitation and emission wavelength. The anisotropy data are interpreted in terms of a model for tryptophan fluorescence depolarization that includes the effects of vibronic coupling and vibrational relaxation. Our results indicate that the fluorescence anisotropy will be an ambiguous method of studying protein motion for times less than 5-10 ps.

Parameters that determine the wavelength of a passive mode-locked dye laser

We introduce a new stability criterion that should be added to previous theoretical models of passive mode locked lasers in order to predict emission wavelength, which is to require that the pulse spectrum reproduces itself after one transit. The CPM laser consisting of rhodamine 6G as gain medium and DODCI as saturable absorber is studied. The relative population balance of the fundamental and photoisoner species of the DODCI are computed as a function of the pulse energy and wavelength. The necessity of a spectral stability criterion follows from the dependence of the gain profile on the pulse parameters. Use of the criterion is shown to agree with previous experimental results, such as the red spectral region of emission and dependence of emission wavelength on absorber concentration. This criterion is expected to be an useful tool in order to select other dye combinations and predict the laser behavior.

Dependence of emission wavelength on cavity length and facet reflectivities in multiple quantum well semiconductor lasers

The spectral emission characteristics of multiple quantum well semiconductor lasers of the Fabry–Perot type are a strong function of laser cavity length and mirror reflectivities. 15 nm theoretically predicted wavelength shifts were validated experimentally. This has immediate applications in the development of semiconductor laser-pumped solid-state lasers, where accurate control of the semiconductor laser pump spectral emission is essential.

ON THE WAVELENGTH DEPENDENCE OF APPARENT EMISSIVITY OF ASTEROID MICROWAVE EMISSIONS: CERES AND VESTA

ABSTRACT Observations of Ceres and Vesta demonstrate the need for modifying the physical parameters of the standard model procedure in treating single-wavelength observations. It is suggested that simultaneous IR and cm-wavelength data should be used in order to determine such properties as the surface dielectric characteristics, layer depth, and radio emissivity. If using the standard model, an emissivity of 0.8 should be adopted for wavelengths of longer than 1 cm.

Energy selection experiments in glassy matrices: The fluorescence spectrum of a synthetic isobacteriochlorin

The fluorescence spectrum of a synthetic isobacteriochlorin was studied in an glassy matrix at 4 K. It consists of a strong OO band and very little vibronic structure. Excitation into a region 400–900 cm −1 above the S 1—S 0 origin with a narrow-band laser results in well structured and excitation wavelength dependent emission spectra. A site selection effect is shown to be responsible for this behaviour.

Emission wavelength-dependent decay of the 9-anthroyloxy-fatty acid membrane probes

Using the phase-modulation technique, we have measured the fluorescence decay of 2- and 12-(9-anthroyloxy)-stearic acid (2- and 12-AS) and 16-(9-anthroyloxy)-palmitic acid (16-AP) bound to egg phosphatidylcholine vesicles or dissolved in nonpolar solvents. Heterogeneity analysis demonstrates that the decay is generally not monoexponential and exhibits large component variations across it emission spectrum. The mean decay time increases (and in parallel, the steady-state polarization decreases) monotonically with increasing wavelength from values at the blue end. The decay at the red side of the emission spectrum contains an exponential term with a negative amplitude, indicating that emission occurs from intermediates created in the excited-state. This behavior is interpreted as arising from intramolecular fluorophore relaxation occurring on the time scale of the fluorescence lifetime. We believe this to be the first study of wavelength-dependent fluorescent emission which is dominated by an intramolecular relaxation process. Although the three probes exhibit qualitatively similar effects, the emission band variations are greatest for 2-AS and smallest for 16-AP. The differences among the probes are not entirely due to environmental factors as demonstrated, for example, by the emission polarization differences observed in the isotropic solvent paraffin oil. In summary, while these findings point out some of the complexities in the 9-anthroyloxy-fatty acids as membrane probes, they also indicate how these complexities might be used as a sensitive measure of lipid-probe interaction.

CW electrooptical properties of InGaAsP(λ = 1.3 µm) buried-heterostructure lasers

The fabrication procedure, electrical properties, optical-bean characteristics, spectral characteristics, and temperature dependence of emission wavelength and threshold of InGaAsP buried-heterostructure (BH) lasers emitting at 1.3 μm are described. The dimensional requirements for fundamental-transverse mode operation have been determined. BH devices are characterized by low threshold currents, fundamental transverse mode operation, linear light output, and narrow spectral width. For 380 μm long devices threshold currents of 40 mA, slope efficiencies of 18 percent, forward resistance of 5 Ω, and T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> values of 75 K have been attained.

Far-infrared emission line and continuum observations of NGC 7027

view Abstract Citations (19) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-infrared emission-line and continuum observations of NGC 7027. Melnick, G. ; Russell, R. W. ; Gull, G. E. ; Harwit, M. Abstract The first observation of a fine-structure transition in NGC 7027 at wavelengths greater than 30 microns is reported. The flux in the 63.2-micron line is found to be approximately 10 to the -16th W/sq cm. It is noted that if NGC 7027 lies at 1 kpc, this corresponds to a luminosity, in the line, approximately 30 times greater than the solar luminosity. The flux of the 88.35-micron line is less than 10 to the -17th W/sq cm, and the upper limit to the line flux at 51.8 microns is found to be 10 to the -16th W/sq cm. These upper limits imply an electron density that is less than 1.6 x 10 to the 5th/cu cm. It is noted that the continuum measurements obtained support a dust temperature of 90 K with an emissivity approximately equal to the reciprocal of the square of the wavelength. The data exclude grain materials whose wavelength-dependent emissivity (the reciprocal of the wavelength raised to nth power) requires n to be outside the range between 1.6 and 2, unless the temperature varies drastically across the dust cloud Publication: The Astrophysical Journal Pub Date: January 1981 DOI: 10.1086/158580 Bibcode: 1981ApJ...243..170M Keywords: Far Infrared Radiation; Infrared Astronomy; Infrared Spectra; Oxygen Spectra; Planetary Nebulae; Continuous Radiation; Cosmic Dust; Fine Structure; Astronomy full text sources ADS | data products SIMBAD (1)