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1.
The temperature dependence of three principal refractive indices of the biaxial KGd(WO4)2 and KY(WO4)2 crystals in the temperature range of 288–673 K was measured at wavelengths of 438.5 and 632.8 nm. Their thermo-optical coefficients
(TOC) of the first and second orders were determined on the basis of the experimental data obtained. TOC were found to be
negative for the ng and np refractive indices of the KY(WO4)2 crystal and for the ng refractive index of the KGd(WO4)2 crystal. It was established that in a fairly wide temperature range contributions of the positive and negative TOC to the
refractive index of a light wave propagating in these crystals in certain directions compensate each other. Such athermal
directions were determined for the index ellipsoid principal planes of these crystals on the basis of experimental data.
PACS 78.20.Ci; 78.20.Nv 相似文献
2.
We studied the visible and IR dispersion of absorption coefficient and refractive index for congruent LiNbO3 and Mg:LiNbO3 crystals before and after chemical reduction at different annealing temperatures. The concentration of Mg in Mg:LiNbO3 samples was just below or above the photorefractive threshold. The reduction-induced changes in the absorption coefficient reveal the formation of polarons typical for doped LiNbO3 crystals. It was shown that the polaron concentration is maximal when the Mg concentration is just below the photorefractive threshold and the annealing temperature is near 500 °C. This temperature is optimal for the most efficient polaron formation at all considered concentrations of Mg. The fitting of the experimental absorption dispersion curves indicates that intermediate polarons are formed in LiNbO3:Mg crystals preferably. The spectral dependence of transmission for samples of lithium niobate of various thicknesses was studied. The results indicate that there are spatial regions with much greater absorption than that of bulk crystals. We assume that, in general, polarons are localized in thin near-surface regions. The spectral dependence of the refractive index in the vicinity of the phonon absorption edge indicates some essential changes of the phonon subsystem taking place after reduction. The infrared contribution into the dispersion of the dielectric function real part increases considerably after reduction. PACS 71.38.Ht; 71.38.-k; 78.20.Ci 相似文献
3.
Yttrium formate dihydrate, Y(HCOO)3·2H2O (point group 222), a promising new material for Raman laser frequency converters, has been reinvestigated with respect to
the linear and nonlinear optical (second-harmonic generation, SHG) properties. High-precision data of refractive indices and
their dispersion in the wavelength range 365–1083 nm are given, together with the three independent components of the tensor
of nonlinear optical susceptibility (SHG) [dijk
SHG]. A calculation of the macroscopic nonlinear optical susceptibility from the hyperpolarizabilities of the formate groups
results in good agreement with the experimental values. This signals that the nonlinear optical interaction in Y(HCOO)3·2H2O can mainly be attributed to the formate groups.
PACS 42.65.Ky; 42.70.Mp; 78.20.Ci 相似文献
4.
A. Bouhemadou Y. Al-Douri R. Khenata K. Haddadi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(2):185-194
We have investigated the structural, elastic, electronic, optical and
thermal properties of c-SiGe2N4 by using the ultrasoft
pseudopotential density functional method within the generalized gradient
approximation. The calculated structural parameters, including the lattice
constant, the internal free parameter, the bulk modulus and its pressure
derivative are in agreement with the available data. The independent elastic
constants and their pressure dependence, calculated using the static finite
strain technique, satisfy the requirement of mechanical stability,
indicating that c-SiGe2N4 compound could be stable. We derive the
shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients
for ideal polycrystalline c-SiGe2N4 aggregate in the framework of
the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of
this compound from the average sound velocity. Band structure, density of
states, Mulliken charge populations and pressure coefficients of energy band
gaps are investigated. Furthermore, in order to understand the optical
properties of c-SiGe2N4, the dielectric function, refractive index,
extinction coefficient, optical reflectivity and electron energy loss are
calculated for radiation up to 40 eV. Thermal effects on some macroscopic
properties of c-SiGe2N4 are predicted using the quasi-harmonic
Debye model in which the lattice vibrations are taken into account. We have
obtained successfully the variations of the primitive cell volume, volume
expansion coefficient, heat capacities and Debye temperature with pressure
and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first
time, the numerical estimates of the elastic constants and related
parameters, and the thermal properties are performed for
c-SiGe2N4. 相似文献
5.
The nonlinear optical properties of thin films of LaEr(MoO4)3 were studied using a ∼30 ps Nd:YAG laser at 532 nm with a repetition rate of 250 Hz. Closed aperture Z-scan measurement revealed
a negative nonlinearity in the LaEr(MoO4)3. The nonlinear refractive index γ=1.38×10-10 cm2/W and nonlinear absorption coefficient β=16.8×10-6 cm/W were calculated from the Z-scan data. The fluorescent upconversion spectra were recorded with 980 nm excitation. An
optical switching mechanism based on nonlinear absorption is also presented experimentally.
PACS 81.15.Fg; 77.84.Bw; 33.50.Dq; 42.70.Mp 相似文献
6.
A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under
the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed
model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals
of KH2PO4 (KDP) and NH4H2PO4 (ADP) on a wide temporal scale (10−8–10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced
transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced
defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and
other experimental conditions have been considered. 相似文献
7.
We present results of the characterization of the nonlinear refractive index of the laser crystal Yb:KGd(WO4)2 using a z-scan technique over the 800–1600 nm wavelength range. Based on our experimental and theoretical results we conclude that Yb:KGW crystal is a good candidate for efficient Kerr-lens mode locking. PACS 42.65.An; 42.65.Hw; 42.55.Rz; 42.65.Re 相似文献
8.
V. Yo. Stadnyk M. O. Romanyuk B. V. Andrievsky Z. O. Kogut 《Optics and Spectroscopy》2010,108(5):753-760
The influence of uniaxial pressure applied along the principal crystallophysical directions on the dispersion and temperature
dependences of the refractive indices n
i
of K2ZnCl4 crystals has been investigated. The n
i
values are found to be fairly sensitive to uniaxial pressure, whereas an uniaxial stress does not change the behavior of
the dispersion and temperature dependences of n
i
. The baric changes in n
i
have been studied. The electronic polarizability α
i
, refractions R, and parameters of UV oscillators (λ0i
, B
1i
) of mechanically deformed K2ZnCl4 crystals have been calculated. The contributions of UV and IR oscillators to n
i
(λ) have been estimated for different temperatures, spectral regions, and stresses. A significant baric shift of the points
of the paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature ranges, depending on
the direction of pressure application, is found; this shift is due to the effect of uniaxial stress on the K2ZnCl4 crystal structure. 相似文献
9.
V. I. Stadnyk M. Ya. Rudish P. A. Shchepansky I. M. Matviishyn V. M. Gaba O. M. Gorina 《Optics and Spectroscopy》2018,124(2):216-220
The infrared reflection spectra of mechanically free and uniaxially compressed LiNH4SO4 crystals are studied for the first time in the spectral range of 800–1700 сm–1 along three crystallophysical directions. The Kramers–Kronig dispersion relations are used to determine the dispersion and baric dependences of refractive index n and the real ε1 and imaginary ε2 parts of the dielectric constant and to calculate the frequencies of longitudinal ωLO and transverse ωТO vibrations, decay constant γ, and oscillator strength f of mechanically free and compressed LiNH4SO4 crystals. The considerable changes observed in the main reflection bands are explained by the effect of uniaxial pressures on the NH4 and SO4 tetrahedra. 相似文献
10.
Y. Wei C. Tu H. Wang F. Yang G. Jia Z. You J. Li Z. Zhu Y. Wang 《Applied physics. B, Lasers and optics》2007,86(3):529-535
A Tm3+-doped NaLa(WO4)2 single crystal with a dimension of Φ20 mm×40 mm was grown by the Czochralski method. Anisotropic thermal expansion coefficients
of this crystal were investigated. Polarized absorption spectra, emission spectra and decay curve were recorded at room temperature.
The absorption and emission cross-section were presented. Based on the Judd–Ofelt analysis, we obtained the three intensity
parameters: Ω2=10.21×10-20, Ω4=2.66×10-20, and Ω6=1.46×10-20 cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Tm3+:NaLa(WO4)2 were calculated, too. Luminescence lifetime of the 3
H
4 level was measured to be 220 μs. The stimulated emission cross-section for the 3
F
4→3
H
6 transition were determined using the reciprocity method, potential laser gain for this transition were also investigated,
the gain curves implied that the tunable range is up to 200 nm.
PACS 42.70.Hj; 78.20.-e 相似文献
11.
V. I. Lukanin D. S. Chunaev A. Ya. Karasik 《Journal of Experimental and Theoretical Physics》2011,113(3):412-421
The nonlinear process of two-photon interband absorption is studied in tungstate and molybdate oxide crystals excited by a
sequence of high-power picosecond pulses with a wavelength of 523.5 nm. The transmission of the crystals is measured for the
excitation pulse intensity up to 100 GW/cm2. The pulse intensity in the crystals initially transparent at a wavelength of 523.5 nm is strongly limited due to two-photon
absorption (TPA), and the reciprocal transmission in PbWO4 and ZnWO4 crystals reaches 50–60. In all crystals, TPA induces long-lived one-photon absorption, which affects the nonlinear process
dynamics and leads to a hysteresis in the dependence of the transmission on the laser excitation intensity. Absorption dichroism
manifests itself in a significant difference in the transmission intensities when the principal orthogonal optical axes of
the crystals are excited. The TPA coefficients are determined during the excitation of two optical axes of the crystals. TPA
coefficients β for the crystals vary over a wide range, namely, from β = 2.4 cm/GW for PbMoO4 to β = 0.14 cm/GW for CaMoO4, and the values of β can differ almost threefold when different optical axes of a crystal are excited. Good agreement is
achieved between the measured intensities limited by TPA and the estimates calculated from the measured nonlinear coefficients.
Stimulated Raman scattering (SRS) upon excitation at a wavelength of 523.5 nm is only detected in two of the four crystals
under study. The experimental results make it possible to explain the suppression of SRS by its competition with TPA, and
the measured nonlinear coefficients are used to estimate this suppression. 相似文献
12.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献
13.
V. I. Stadnyk N. A. Romanyuk M. R. Tuzyak R. S. Brezvin I. M. Matviishin V. M. Gaba 《Optics and Spectroscopy》2008,104(6):870-874
The effect of uniaxial mechanical pressure σ m ≤ 150 bar on the spectral (300–800 nm) dependence of the birefringerence Δn i and refractive indices n i of (NH4)2SO4 crystals has been investigated. It is shown that the dispersion of n i (λ) and Δn i (λ) is normal and sharply increases with approach to the absorption edge. It is established that uniaxial pressure does not change the character of the dispersions dn i /dλ and dΔn i /dλ and only affects their magnitudes. It is shown that the increase in the refractive indices under uniaxial stress is mainly due to the increase in the refraction caused by the increase in the band gap and long-wavelength shift of the UV absorption band maximum. 相似文献
14.
Spectral dependences of the relative permittivity ɛ = ɛ1 − iɛ2 of a uniaxial weak ferromagnet FeBO3 are measured for two principal polarizations in the energy range 0.6–5.6 eV. The positions have been determined for the charge-transfer
transitions that make the main contribution to absorption above the bandgap and determine the refractive-index dispersion
below the bandgap. The isotropic magnetic contribution to the refractive index has been detected by studying the temperature
dependence of the refractive index in the range 100–700 K; its value (≈2 × 10−2) is found to be record high for magnetic dielectrics. The energy shift of the effective oscillator, which characterizes the
shift of the positions of the charge-transfer transitions due to magnetic ordering, is determined from these data within the
framework of a single-oscillator model. The value of the exchange striction in FeBO3 is determined from optical measurements. 相似文献
15.
D. V. Volkov A. A. Demidov N. P. Kolmakova 《Journal of Experimental and Theoretical Physics》2007,104(6):897-905
The field and temperature dependences of magnetization and the temperature dependences of the initial magnetic susceptibility have been theoretically studied for three crystallographic directions in a trigonal NdFe3(BO3)4 antiferromagnetic crystal. The calculations were performed using a molecular field approximation and a crystal field model for the rare-earth subsystem. The obtained theoretical expressions are applied to the interpretation of recent experimental data [1–4] on the magnetic properties of NdFe3(BO3)4. The results of calculations show a good agreement with experiment. The proposed theory adequately describes (i) anomalies of the Schottky type in the temperature dependence of the magnetic susceptibility, (ii) nonlinear curves of magnetization in the basal plane in a magnetic field up to 1 T (showing evidence of the first-order phase transitions) and their evolution with the temperature, and (iii) the field and temperature dependences of magnetization in a magnetic field up to 9 T. 相似文献
16.
A nonlinear effect of spatiotemporal transformations of a focused linearly polarized Gaussian beam of a He-Ne laser obliquely incident (S and P polarizations) upon an As2S3-Ag film containing a small amount of chlorine and deposited onto a glass substrate is found and interpreted. The effect consists in the appearance, in the process of exposure, of beams diffracted and anisotropically scattered by periodic structures arising due to excitation of the waveguide TE0 and TM0 modes in the film. The diffraction measurements of the effective refractive indices for the TE0 and TM0 modes make it possible to calculate the refractive index and the thickness of the film from dispersion equations. Along with slow evolution of the diffraction and scattering patterns, we have found a persistent optical turbulence in the fringes of scattering from the structures related to excitation of the TE0 modes. It is suggested that the turbulence is an indication of existence of reversible processes in the mechanism of photosensitivity. 相似文献
17.
The exciton absorption spectra of thin films of (Cs1 − x
Rb
x
)2CdI4 solid solutions have been investigated and the refractive index n(λ) in their transparency window in the concentration range of 0 ≤ x ≤ 1 has been measured. The exciton-band parameters and optical permittivity ɛ∞(x) have been found to linearly depend on the concentration. It is established that excitons are incorporated into the CdI2 sublattice of the solid solutions and belong to intermediate-coupling ones. The characteristics of excitons in ferroelastics
are compared with the corresponding parameters for CdI2, RbI, and CsI, which are used as components to synthesize ternary compounds. 相似文献
18.
The thermal effects produced by continuous-wave laser radiation on free-standing Si/SiO2 superlattices are studied. We compare two samples with different SiO2 layer thicknesses (2 and 6 nm) and the same Si layer thickness (2 nm). The as-prepared free-standing superlattices contain
some amount of Si nanocrystals (Si-nc). Intense laser irradiation at 488 nm of the as-prepared samples enhances the Raman
scattering of Si-nc by two orders of magnitude. This laser-induced crystallization originates from melting of Si nanostructures
in silica, which makes Si-nc better ordered and better isolated from the oxide surrounding. Continuous-wave laser control
of Si-nc stress was achieved in these samples. In the proposed model, intense laser radiation melts Si-nc, and Si crystallization
upon cooling down from the liquid phase in a silica matrix leads to compressive stress. The Si-nc stress can be tuned in the
∼3 GPa range using laser annealing below the Si melting temperature. The high laser-induced temperatures were verified with
Raman spectroscopy. The laser-induced heat leads to a strongly nonlinear rise of light emission. The light emission is also
observed in the anti-Stokes region, and its temperature dependence is practically the same for the two studied samples. The
laser-induced temperature is essentially controlled by the absorbed laser power.
PACS 78.55.-m; 78.20.-e; 68.55.-a; 78.30.-j 相似文献
19.
The nonlinear microwave absorption in the (CH3NH3)2CuBr4 antiferromagnetic crystal is investigated experimentally. The temperature and angular dependences of the parameters of nonlinear resonance and the dependences of these parameters on the microwave pump power are analyzed. It is found that the nonlinear properties deteriorate with decreasing temperature and the linear and nonlinear contributions are competitive in character. 相似文献
20.
G.S. Wang D. Rémiens E. Dogheche X.L. Dong 《Applied Physics A: Materials Science & Processing》2007,88(4):657-660
PbZr0.53Ti0.47O3/LaNiO3 (PZT/LNO) hetero-structures have been successfully deposited on MgO, SrTiO3, Al2O3 and Si substrate by chemical solution routes, respectively. The X-ray diffraction measurements show that out-of-plane lattice
parameters of PZT increase as increase of thermal expansion coefficient of substrate. Polarization fatigues of Pt/PZT/LNO
capacitors are strongly affected by the thermal strain caused by difference of thermal expansion coefficient between PZT and
substrate materials. High fatigue resistance of Pt/PZT/LNO can be obtained by using substrate with similar thermal expansion
coefficient as PZT.
PACS 77.84.Dy; 78.20.Ci; 81.20.Fw 相似文献