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Results for “absorption saturation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Nanosecond and ultrafast optical power limiting in luminescent Fe{sub 2}O{sub 3} hexagonal nanomorphotype

Nonlinear optical absorption and optical power limiting properties of Fe{sub 2}O{sub 3} hexagonal nanomorphotype are investigated using open aperture Z-scan technique with the 5 ns and 100 fs laser pulses, at 532 nm and 800 nm excitation domains. At relatively low pulse energies (below 5 μJ), sample shows saturable absorption (SA), but on going to the higher energies an interesting switchover from saturable absorption to effective two photon absorption is observed in both excitation domains. The magnitude of effective two photon absorption coefficients is calculated to be in the range of 10{sup −10} m/W for nanosecond and 10{sup −15} m/W for femtosecond laser pulse energies, respectively. XRD and TEM study reveals the polycrystalline nature, hexagonal morphology, and size of the nanostructure. The luminescence emission property is examined by photoluminescence spectroscopy (PL). It is found that some strange features exist in the luminescence spectra that are consistent with the nanoparticles size distribution. The PL emission lines are explained as originated from various optical band edges due to the size induced quantum confinement and band gap resonant PL absorption/emission behavior of semiconductor nanostructures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Graphene-doped polymer nanofibers for low-threshold nonlinear optical waveguiding

Graphene-doped polymer nanofibers are fabricated by taper drawing of solvated polyvinyl alcohol doped with liquid-phase exfoliated graphene flakes. Nanofibers drawn this way typically have diameters measured in hundreds of nanometers and lengths in tens of millimeters; they show excellent uniformity and surface smoothness for optical waveguiding. Owing to their tightly confined waveguiding behavior, light–matter interaction in these subwavelength-diameter nanofibers is significantly enhanced. Using approximately 1350-nm-wavelength femto-second pulses, we demonstrate saturable absorption behavior in these nanofibers with a saturation threshold down to 0.25 pJ pulse -1 (peak power ~1.3 W). Additionally, using 1064-nm-wavelength nanosecond pulses as switching light, we show all-optical modulation of a 1550-nm-wavelength signal light guided along a single nanofiber with a switching peak power of ~3.2 W.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Polarization Phenomena in Transparency and Absorption Effects Induced by the Field of Unidirectional Waves

Physical processes that form the spectra of saturated absorption and magnetic scanning resonances on an atomic transition with level momentum J = 1 in the field of unidirectional waves of arbitrary intensity under variation in their polarization directions are investigated by numerical simulation and analytically. It is shown that anomalies in nonlinear resonance spectra are determined by the polarization of the waves and the degree of openness of the atomic transition, while anomalies in the experimentally observed magnetic scanning spectra are attributed to the magnetic coherence induced by the fields directly on the levels of the lower state, rather than to its transfer from the excited states, as was assumed earlier.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Self-diffraction of ultrashort laser pulses under resonant excitation of excitons in a colloidal solution of CdSe/ZnS quantum dots

We report self-diffraction processes of two types under resonant excitation of the fundamental electron – hole (exciton) transition in a strongly absorbing colloidal solution of CdSe/ZnS quantum dots (QDs) by high-power picosecond laser pulses. In the first case the absorption saturation (bleaching) at the exciton transition frequency and the Stark shift of exciton absorption line lead to the formation of a transparency channel and self-diffraction of the laser beam from the thus induced round diaphragm. In the second case, self-diffraction of two laser beams, intersecting in a cell with a colloidal QD solution, occurs on the diffraction grating induced by these beams. The physical processes responsible for the nonlinear optical properties of CdSe/ZnS QDs and the found selfaction effects are analysed. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Frequency modulation of semiconductor disk laser pulses

A numerical model is constructed for a semiconductor disk laser mode-locked by a semiconductor saturable absorber mirror (SESAM), and the effect that the phase modulation caused by gain and absorption saturation in the semiconductor has on pulse generation is examined. The results demonstrate that, in a laser cavity with sufficient second-order dispersion, alternating-sign frequency modulation of pulses can be compensated for. We also examine a model for tuning the dispersion in the cavity of a disk laser using a Gires–Tournois interferometer with limited thirdorder dispersion. (control of radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Effect of nonlinear absorption on electric field applied lead chloride by Z-scan technique

The preparation, spectral response and optical nonlinearity of gel grown lead chloride single crystals subjected to electric field of 20V using parallel plate arrangements have been investigated. Optical band gap of the samples were determined using linear absorption spectra. Open aperture z-scan was employed for the determination of nonlinear absorption coefficient of PbCl{sub 2} solution. The normalized transmittance curve exhibits a valley shows reverse saturable absorption. The non linear absorption at different input fluences were recorded using a single Gaussian laser beam in tight focus geometry. The RSA nature of the sample makes it suitable for optical limiting applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Nonlinear transmission of CO{sub 2} laser radiation by graphene

The nonlinear transmission of multilayer ({approx}12 layers) graphene at the wavelength {lambda} {approx} 10 {mu}m is measured for the first time. The absorption saturation intensity in graphene ({approx}330 kW cm{sup -2}) and the ablation threshold of its outer layers ({approx}1 MW cm{sup -2}, 0.11 J cm{sup -2}) under action of a CO{sub 2} laser pulse with a duration of 70 - 85 ns at {lambda} = 10.55 {mu}m are determined. The residual absorption of graphene at its partial saturation was 48 % of the initial value. This is significantly smaller than the value measured previously for samples with a close number of layers at {lambda} = 1.55 {mu}m (92.3 % - 93.8 %). It is shown that the ablation threshold of two graphene layers adjacent to the BaF{sub 2} substrate (after successive ablation of outer layers) exceeds 0.27 J cm{sup -2}. (nonlinear optical phenomena)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Third order nonlinear optical properties of bismuth zinc borate glasses

Third order nonlinear optical characterization of bismuth zinc borate glasses are reported here using different laser pulse durations. Bismuth zinc borate glasses with compositions xBi{sub 2}O{sub 3}-30ZnO-(70-x) B{sub 2}O{sub 3} (where x = 30, 35, 40, and 45 mol. %) have been prepared by melt quenching method. These glasses were characterized by Raman, UV-Vis absorption, and Z scan measurements. Raman and UV-Vis spectroscopic results indicate that non-bridging oxygens increase with increase of bismuth content in the glass. Nonlinear absorption and refraction behavior in the nanosecond (ns), picosecond (ps), and femtosecond (fs) time domains were studied in detail. Strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with both ps and fs excitations. In the case of ns pulse excitations, TPA and free-carrier absorption processes contribute for the nonlinear absorption. Two-photon absorption coefficient (β) and the absorption cross section due to free carriers (σ{sub e}) are estimated by theoretical fit of the open aperture Z-scan measurements and found to be dependent on the amount of bismuth oxide in the glass composition. In both ns and fs regimes the sign and magnitude of the third order nonlinearity are evaluated, and the optical limiting characteristics are also reported.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Ca L 2,3 -edge near edge X-ray absorption fine structure of tricalcium aluminate, gypsum, and calcium (sulfo)aluminate hydrates

Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoaluminate hydrate (abbreviated as kuzelite) are the major minerals in the hydration reaction of tricalcium aluminate in the presence of gypsum and have critical impacts on the kinetics and thermodynamics of early-age cement hydration mechanisms. In this paper, spectroscopic analysis of these minerals is conducted using scanning transmission X-ray microscopy (STXM). Their Ca L 2,3 -edge near edge X-ray absorption fine structure (NEXAFS) spectra are measured and correlated to the known Ca coordination environments. The results indicate that these minerals have unique Ca environments that can be differentiated from one another based on the intensities and positions of the absorption peaks at 346.5–348.5 and 350.5–351.5 eV. It is concluded that Ca in tricalcium aluminate (cubic and orthorhombic polymorphs) and katoite is in cubic-like coordination with negative 10Dq, whereas Ca is in an octahedral-like coordination with positive 10Dq in ettringite, gypsum, and kuzelite. For tricalcium aluminate, the Ca atoms in both polymorphs are in similar chemical environments with slightly more distortion in the orthorhombic polymorph. As a common issue in STXM experiments, absorption saturation of NEXAFS spectra is also investigated. It is demonstrated that the optical density difference between pre- and post-edge absorption levels provides a reliable indication of the sample thickness in the systems studied. Finally, the present work provides a reference for the STXM study of the calcium (sulfo)aluminate reactions in cement hydration and natural aqueous environments, and in the former case, provides a more complete understanding of a system that may serve as a low-C alternative to Portland cement.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nonlinear bleaching, absorption, and scattering of 532-nm-irradiated plasmonic nanoparticles

Single-pulse irradiation of Au and Ag suspensions of nanospheres and nanodisks with 532-nm 4-ns pulses has identified complex optical nonlinearities while minimizing material damage. For all materials tested, we observe competition between saturable absorption (SA) and reverse SA (RSA), with RSA behavior dominating for intensities above {approx}50 MW/cm{sup 2}. Due to reduced laser damage in single-pulse experiments, the observed intrinsic nonlinear absorption coefficients are the highest reported to date for Au nanoparticles. We find size dependence to the nonlinear absorption enhancement for Au nanoparticles, peaking in magnitude for 80-nm nanospheres and falling off at larger sizes. The nonlinear absorption coefficients for Au and Ag spheres are comparable in magnitude. On the other hand, the nonlinear absorption for Ag disks, when corrected for volume fraction, is several times higher. These trends in nonlinear absorption are correlated to local electric field enhancement through quasi-static mean-field theory. Through variable size aperture measurements, we also separate nonlinear scattering from nonlinear absorption. For all materials tested, we find that nonlinear scattering is highly directional and that its magnitude is comparable to that of nonlinear absorption. These results indicate methods to improve the efficacy of plasmonic nanoparticles as optical limiters in pulsed laser systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Spectroscopy of GR1 centers in synthetic diamonds

We report on the spectroscopic characterization, absorption saturation, and excited-state dynamics of GR1 centers in synthetic diamonds. The non-linear optical measurements reveal an efficient bleaching of the GR1 center’s ground level under ns-pulsed 633 nm excitation. The maxima of absorption and emission cross sections were estimated to be 4.5 × 10 −17 cm 2 and 9 × 10 −17 cm 2 at 630 nm and 780 nm, respectively. The radiative lifetime of the excited level was estimated to be 8.5 ns. The 658 nm probe kinetics uncovered relaxation of 1 T 2 excited level going predominantly to a metastable state with a lifetime of 220 μs. An induced absorption detected with the use of a highly concentrated diamond sample could be due to up-conversion and photoionization processes in additional impurity-vacancy center with absorption at the short-wavelength tail of GR1. The results presented here indicate that synthetic diamonds with GR1 centers could serve as near infrared gain media or passive Q-switchers for laser cavities over the 633–750 nm spectral range. Optimization of the center concentration and the crystal parameters are required to minimize the induced absorption at the lasing wavelengths.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Luminescence and Nonlinear Optical Properties of Hybrid Associates of Ag{sub 2}S Quantum Dots with Molecules of Thiazine Dyes

Spectral, kinetic, and nonlinear optical regularities that demonstrate the exchange of electronic excitations between the components of hybrid associates of Ag{sub 2}S colloid quantum dots (1.7–1.8 nm) in gelatin with molecules of thiazine dyes (Ds) are found. When the IR luminescence of Ag{sub 2}S quantum dots (QDs) is excited by radiation from the thionine absorption region, its enhancement due to nonradiative resonant energy transfer is observed. The association with methylene-blue molecules blocked the IR luminescence of Ag{sub 2}S QDs upon its excitation by radiation from the absorption region of the dye due to the transfer of charge carriers. It is demonstrated that the hybrid association of thionine molecules and Ag{sub 2}S QDs adversely affects the nonlinear optical properties of the latter, which manifests itself in inverse saturated absorption by the action of 10-ns second-harmonic pulses (532 nm) of a Nd{sup 3+}:YAG laser. For the associates of Ag{sub 2}S QDs with methylene-blue molecules, the radiation focusing caused by the transfer of charge carriers from the dye and the change in the population of small traps in nanocrystals is found. It is concluded that the direction of the transfer of electronic excitations and the photophysical processes in these objects are determined by the mutual arrangement of the HOMO–LUMO levels of the dye with respect to the levels of dimensional quantization of the Ag{sub 2}S QDs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Absorption spectra and nonlinear transmission (at λ = 2940 nm) of a diffusion-doped Fe{sup 2+}:ZnSe single crystal

Transmission spectra of a ZnSe sample diffusion-doped with Fe{sup 2+} ions have been measured in the wavelength range 500 – 7000 nm. A broad absorption band in the range 500 – 1500 nm has been observed in both doped and undoped regions of the sample. This band is possibly due to deviations from stoichiometry in the course of diffusion doping. The transmission of the Fe{sup 2+}:ZnSe sample at a wavelength of 2940 nm has been measured at various dopant concentrations and high peak pulse intensities (up to 8 MW cm{sup -2}). The samples have been shown to be incompletely bleached: during a laser pulse, the transmission first increases, reaches a maximum, and then falls off. Our results suggest that the incomplete bleaching cannot be accounted for by excited-state absorption. The incomplete bleaching (as well as the transmission maximum) is due to the heating of the sample, which leads to a reduction in upper level lifetime and, accordingly, to an increase in absorption saturation intensity. (nonlinear optical phenomena)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Z-scanning under monochromatic laser pumping: a study of saturatable absorption in a suspension of multiwalled carbon nanotubes

A system has been developed and designed based on a single-mode single-frequency passive Q-switched pulsed YAG : Nd{sup 3+} laser to investigate with high accuracy the nonlinear optical properties of a liquid placed in an optical cell with uncoated input windows. The efficiency of this system is demonstrated by examples of studying the saturable absorption of an aqueous suspension of multiwalled carbon nanotubes and the nonlinear absorption of a colour glass filter ZhS18 at a wavelength of 532 nm. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1990

Ultraviolet interstellar absorption toward HD 163522, a halo star at 9 kiloparsecs in the direction l = 350 deg and b = -9 deg

UV interstellar absorption line measurements obtained by the IUE satellite toward HD 163522 in the direction l = 349.6 deg and b = -9 deg are analyzed. The UV stellar spectrum of HD 163522 places the star beyond the Galactic center at a distance away from the Galactic plane of z = -1.5 kpc. An absorption-line spectrum with S/N approximately equal to 15-25 is produced. The UV interstellar absorption lines for neutral, and weakly and highly ionized gas are examined, as well as the correlation between profiles and the Galactic rotation. Simple model calculations are performed to quantitatively determine the characteristics of the profiles. The observed absorption-line profiles for Al III, Si IV, C IV, and N V are converted into plots of optical depths vs velocity. A comparison of these plots for the weak and strong member of each doublet reveals that the profiles are not strongly influenced by the presence of unresolved saturated absorption, and the optical depth profiles can therefore be directly converted into measures of N(v), the column density per km/s. The converted column densities are examined.

Savage, Blair D.↗
DOE OSTI2022

Gamma-radiation-induced negative nonlinear absorption in quartz glass

The effect of ionizing radiation on the nonlinear optical properties of materials needs to be considered for applications that employ high-power laser pulses in extreme radiation environments. The Heraeus Infrasil302 optical quartz glass was irradiated by gamma rays, and its nonlinear absorption was measured using the open-aperture Z-scan technique with nanosecond laser pulses. Irradiation results in a negative nonlinear absorption coefficient whose magnitude increases with irradiation dose. Nonlinear absorption coefficients of -0.78, -1.14, -1.29, and -1.88~ × ~10 -13 m/W are measured for gamma doses of 600 krad, 1.2 Mrad, 3.6 Mrad, and 10 Mrad, respectively. Thermal annealing restores the optical properties of quartz-glass to their unirradiated values. It is suggested that metallic impurities introduced by the manufacturing process have a role in inducing saturated absorption in irradiated quartz glass, which manifests as negative nonlinear absorption coefficient, and is demonstrated by comparing Infrasil302 quartz results to equivalent irradiated measurements for Spectrosil2000 quartz.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

Charge transfer in graphene oxide-dye system for photonic applications

The fluorescence of a standard dye Rhodamine 6G (R6G) in solution decreases on addition of reduced graphene oxide (rGO). The absorption spectra and lifetime measurements confirm that no excited-state but a ground-state complex formation is responsible for this effect. For silver decorated rGO (Ag-rGO), the quenching efficiency and ground state complex formation process is small. Z-scan measurements have been done to study the optical nonlinearity at 532 nm under ps time scale. Remarkable reduction in the saturable absorption (SA) effect of R6G indicates no nonlinear contribution from the ground state complex. The results have been explained with varying charge transfer rates and non-fluorescence nature of the complex.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗