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1.
A perturbation theory is put forward that describes the effect of thermal nonlinearity due to the temperature dependence of the thermophysical parameters of high-absorption systems with a low thermal conductivity on the parameters of the photoacoustic signal detected by the gas microphone technique. It is found that the dependence of the photoacoustic signal amplitude on incident beam intensity I 0 stems from the dependence of the illuminated surface temperature on I 0. This dependence is a complicated function instead of being a simple quadratic function as was expected. In the limiting cases (μsβ ? 1 and μsβ ? 1), this contribution to the photoacoustic signal amplitude is described by simple expressions, which are convenient for determining the thermal coefficients of the thermophysical parameters of the medium. It is found that the thermal nonlinearity significantly affects the photoacoustic signal phase in the frequency region meeting the condition μsβ ~ 1. In the above limiting cases, its effect is insignificant. A theory of generation of the photoacoustic signal second harmonic is proposed. The second harmonic is related to the temperature dependence of the thermophysical parameters of the buffer gas and sample. It is shown that the amplitude of the signal is a quadratic function of the incident beam intensity and varies with its frequency as ω?3/2 for μsβ ? 1 and ω?5/2 for μsβ ? 1. 相似文献
2.
A. N. Obraztsov I. Yu. Pavlovskii H. Okushi H. Watanabe 《Physics of the Solid State》1997,39(10):1594-1598
Photoacoustic spectroscopy is used to study optical absorption in diamond powders and polycrystalline films. The photoacoustic
spectra of diamond powders with crystallite sizes in the range from ∼100 μm to 4 nm and diamond films grown by chemical vapor deposition (CVD) had a number of general characteristic features corresponding
to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (∼5.4 eV) and
to absorption in the visible and infrared by crystal-structure defects and the presence of non-diamond carbon. For samples
of thin (∼10 μm) diamond films on silicon, the photoacoustic spectra revealed peculiarities associated with absorption in the silicon substrate
of light transmitted by the diamond film. The shape of the spectral dependence of the amplitude of the photoacoustic signal
in the ultraviolet indicates considerable scattering of light specularly reflected from the randomly distributed faces of
the diamond crystallites both in the polycrystalline films and in the powders. The dependence of the shape of the photoacoustic
spectra on the light modulation frequency allows one to estimate the thermal conductivity of the diamond films, which turns
out to be significantly lower than the thermal conductivity of single-crystal diamond.
Fiz. Tverd. Tela (St. Petersburg) 39, 1787–1791 (October 1997) 相似文献
3.
A. Heidenreich I. Last J. Jortner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):195-202
We present a theoretical and computational study of the properties and the
response of the nanoplasma and of outer ionization in Xen clusters (n =
55–2171, initial cluster radius R0 = 8.7–31.0 ?) driven by
ultraintense near-infrared laser fields (peak intensity IM = 1015–1020 Wcm-2, temporal pulse length τ= 10–100 fs, and frequency ν= 0.35 fs-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of
the fs laser pulse and can either be persistent (at lower intensities of IM = 1015–1016 Wcm-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities
of IM = 1018–1020 Wcm-2 and/or for smaller cluster sizes). The nanoplasma is depleted by outer ionization that was semiquantitatively described by
the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity and pulse length
dependence of the outer ionization yield. The electrostatic model was further utilized for estimates of the laser intensity
and pulse
width dependence of the border radius R0
(I) for the attainment of complete outer ionization at
,
while at R0 > R0
(I) a persistent nanoplasma prevails. R0
(I)
establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense
laser-cluster interactions. 相似文献
4.
We investigate the spectroscopic properties of the 1.5-μm emission from the 4I13/2 → 4I15/2 transition of Er3+ ions in PbO–Bi2O3–Ga2O3–GeO2 glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width
at half-maximum of ∼45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 × 10−20 cm2 and a large product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially
available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating
a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of
the 2H11/2 of Er3+. The results indicate the possibility towards the development of lead–bismuth–gallate–germanate based glasses as photonics
devices. 相似文献
5.
We have investigated the behavior of the intensity of phonon-free lines appearing in the luminescence spectra of Rb3UO2F5 crystals in the 4.2–40 K range due to a pure electron transition and its vibrational recurrences with the frequency of fully
symmetrical stretching vibrations of the uranyl ion. It is shown that the temperature dependence of the total integrated intensity
of these phonon-free lines, IΣ, can be described using a model of configuration coordinates of an impurity center with one local vibration. An empirical
expression has been obtained for the dependence IΣ = IΣ(T) in the form of the product IΣ(T) = I0(T)SΣ(T), where the first factor describes the temperature dependence of the integrated intensity of the pure electron transition
line and the second can be approximated by an exponential function of the Stokes parameter.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 129–131, January–February, 2000. 相似文献
6.
V. Singh V. K. Rai I. Ledoux-Rak H.-Y. Kwak 《Applied physics. B, Lasers and optics》2009,97(1):103-107
The frequency up-conversion, an efficient laser emission and amplification in Er3+:LiAl5O8 phosphors co-doped with Yb3+ and Zn2+ phosphor powders in the 520–560, 640–680 nm regions and at ∼1.5 μm, respectively, have been reported. The emission corresponds
to the 2H11/2, 4S3/2→4I15/2, 4F9/2→4I15/2 and 4I13/2→4I15/2 transitions upon direct excitation into the intermediated 4I11/2 level using ∼980 nm radiation from a CW laser. Possible mechanisms involved for the up-conversion processes based on the
energy level matching scheme, the pump-power dependence and the dynamical behaviour have been discussed. The effect of the
addition of Yb3+ and Zn2+ for the amplification in the 1.5 μm eye-safe telecommunication window has been elaborated and characterized in detail. 相似文献
7.
An HTSC powder sample with grain (particle) diameter of 20–50 μm placed in a dc magnetic field B
0 and cooled to a temperature below the superconducting transition temperature was exposed to the radiofrequency (rf) pulsed
magnetic field B
∼ (B
∼ ⊥ B
0) at a carrier frequency of 30.7 MHz. Stable echo signals were recorded which followed different rf-pulse trains. This phenomenon
has the following mechanism. The rf magnetic field stimulates fluxoid oscillations on the HTSC grain surface, which are transformed
into lattice oscillations through the pinning centers and induce a propagating sound wave. The second-order nonlinearity with
respect to the gradient of the crystal lattice deviation from the equilibrium position taken into account in the sound wave
equation yields the dependence of the crystal lattice natural frequency on the amplitude and length of the pulses which excite
these oscillations. This dependence is responsible for the emergence of echo signals. 相似文献
8.
N. Barreiro A. Vallespi A. Peuriot V. Slezak G. Santiago 《Applied physics. B, Lasers and optics》2010,99(3):591-597
A theoretical expression for the pulsed photoacoustic signal amplitude from NO2–air mixtures is deduced based on a two-level system and the inhomogeneous wave equation, in the limit where the V-T relaxation
time is longer than the laser pulse width (low buffer pressure). In this time limit, the photoacoustic signal from NO2, at constant pressure, after excitation by pulses from a Nd:YAG laser at 532 nm, is measured at different buffer pressures.
The relaxation rates are obtained by measuring the quenching of visible fluorescence induced by the same laser. The experimental
dependence of the photoacoustic signal amplitude on air pressure shows a very good agreement with the model, where the measured
relaxation rates are included. 相似文献
9.
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
10.
L. K. Neudachina E. V. Dedyukhina O. V. Evdokimova N. V. Pechishcheva E. V. Osintseva K. Yu. Shunyaev 《Journal of Applied Spectroscopy》2010,77(2):206-212
The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling
point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ
ex
/λ
fl
max
= 225/290 nm) and unprotonated (λ
ex
/λ
fl
max
= 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated
I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher
than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm3) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm3) and Cd(II) (2–330 mg/dm3) although a similar dependence is not observed at 293 K. 相似文献
11.
M. Bryushinin V. Golubev Y. Kumzerov D. Kurdyukov I. Sokolov 《Applied physics. B, Lasers and optics》2009,95(3):489-495
We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous
glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created
by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal
amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I
0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I
0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L
D=0.18 μm. 相似文献
12.
The dependence of the fundamental and harmonic photothermal (PT) signal on the intensity I
0 of the illumination source is analyzed. It is shown that both components of the PT signal do not increase indefinitely with I
0, but at sufficiently high power densities begin to decrease as 1/I
0. Along with photoacoustic saturation, this defines an upper limit for the sensitivity of spectrometers based on PT detection. 相似文献
13.
We have derived the so-called gap equation, which determines the upper critical magnetic field, perpendicular to conducting chains of a quasi-one-dimensional superconductor. By analyzing this equation at low temperatures, we have found that the calculated angular dependence of the upper critical magnetic field is qualitatively different than that in the so-called effective mass model. In particular, our theory predicts a non-analytical angular dependence of the upper critical magnetic field, H c2(0) − H c2(α) ∼ α3/2, when magnetic field is close to some special crystallographic axis and makes an angle α with it. We discuss possible experiments on the superconductor (DMET)2I3 to discover this non-analytical dependence. 相似文献
14.
N. Venkatram D. Narayana Rao L. Giribabu S. Venugopal Rao 《Applied physics. B, Lasers and optics》2008,91(1):149-156
We report our results on the nonlinear optical and optical limiting properties of two alkoxy phthalocyanines namely 2,3,9,10,16,17,23,24-octakis-(heptyloxy)
phthalocyanine and 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine zinc(II) studied at a wavelength of 532 nm using
6 ns pulses. Using the standard Z-scan technique we observed that both the phthalocyanines exhibited negative nonlinearity
as revealed by the signature of closed aperture data. The magnitude of the nonlinear refractive index n2 evaluated from the closed aperture data was ∼ 1.61×10-11 cm2/W for the free-base phthalocyanine and ∼ 1.56×10-11 cm2/W for the metallic phthalocyanine. Open aperture Z-scan data indicates strong nonlinear absorption in both the phthalocyanines
with measured nonlinear coefficients of ∼ 1650 cm/GW and ∼ 1850 cm/GW respectively. We also report optical limiting properties
of these phthalocyanines with limiting thresholds (I1/2) of ∼ 0.5 J/cm2. Our studies suggest that these phthalocyanines are one of the best molecules for nonlinear optical applications studied
recently.
PACS 42.65.-k; 42.70.Jk, 42.65.Jx 相似文献
15.
Loktionov E. Yu. Ovchinnikov A. V. Protasov Yu. S. Protasov Yu. Yu. Sitnikov D. S. 《Optics and Spectroscopy》2012,112(4):631-637
The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy
efficiency, of the laser ablation of flat polymer targets ((C2F4)
n
, (CH2O)
n
) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs)
of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I
0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation. 相似文献
16.
C. Javaux I.G Hughes G. Lochead J. Millen M. P.A. Jones 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(2):151-154
We have performed polarization spectroscopy on the 5s2
1S0 →5s5p1P1 transition of atomic strontium. The signal is generated by saturation effects, rather than optical pumping, as the ground
state is non-degenerate. This technique generated a dispersion-type lineshape suitable for laser stabilization, without the
need for frequency modulation. The dependence of the amplitude and gradient on intensity and magnetic field were also investigated,
and compared to a related technique based on the circular dichroism induced by a magnetic field. 相似文献
17.
Infrared, visible and upconversion emission of CaAl12O19 powders doped with Er3+, Yb3+ and Mg2+ ions
V. Singh V. K. Rai I.-J. Lee I. Ledoux-Rak K. Al-Shamery J. Nordmann M. Haase 《Applied physics. B, Lasers and optics》2012,106(1):223-228
CaAl12O19 powders doped with Er3+, Yb3+, and Mg2+ ions have been prepared by a low-temperature combustion synthesis technique. Formation and chemical compositions were analysed
by powder X-ray diffraction and energy-dispersive spectroscopy. The visible luminescence spectra of the doped phosphor upon
excitation with ∼378 nm radiation from a Xenon lamp have been studied. A broad band emission in the range of 1400–1700 nm
with a peak around 1.5 μm and FWHM of about ∼80 nm responsible for the eye-safe telecommunication window has been observed
upon direct excitation with a NIR laser into the 4I11/2 level of Er3+. The effect of co-doping with Yb3+ and Mg2+ ions in the CaAl12O19:Er3+ matrix on the photoluminescence intensity corresponding to the 2H11/2,4S3/2→4I15/2, 4F9/2→4I15/2 and 4I13/2→4I15/2 transitions of Er3+ is elaborated and discussed in detail. 相似文献
18.
V. M. Gordienko I. A. Makarov V. P. Petukhov A. S. Khomenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(2):183-188
The dependence of the characteristic X-ray radiation yield from CaF2 crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 1015 W/cm2) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental
conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic
X-ray radiation increased from 6 × 10−8 for the surface up to 10−7 in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source
of X-ray radiation was located near the surface inside the microchannel. 相似文献
19.
Data presented on the influence of the temperature in the range 80–650 K on the spectral kinetics of the luminescence and
transient absorption of unactivated CsI crystals under irradiation by pulsed electron beams (〈E〉=0.25 MeV, t
1/2=15 ns, j=20 A/cm2). The structure of the short-wavelength part of the transient absorption spectra at T=80–350 K exhibits features, suggesting that the nuclear subsystem of self-trapped excitons (STE’s) transforms repeatedly
during their lifetime until their radiative annihilation at T⩾80 K, alternately occupying di-and trihalide ionic configurations. It is established that a temperature-induced increase
in the yield of radiation defects, as well as F and H color centers, and quenching of the UV luminescence in CsI occur in the same temperature region (above 350 K) and are characterized
by identical thermal activation energies (∼0.22 eV). It is postulated that the STE’s in a CsI crystal can have a trihalide
ionic core with either an on-center or off-center configuration; the high-temperature luminescence of CsI crystals is associated
with the radiative annihilation of an off-center STE with the structure (I−(I0I−
e
−))*.
Fiz. Tverd. Tela (St. Petersburg) 40, 640–644 (April 1998) 相似文献
20.
G. V. Kulak 《Journal of Applied Spectroscopy》2000,67(3):510-516
The features of the Bragg diffraction of Gaussian light beams at ultrasound waves in gyrotropic crystals were investigated.
The dependence of the diffraction efficiency on the intensity of an ultrasound beam, the cross-section radius of a light beam,
and their divergence ratio was found. An asymptotic expression for the transverse distribution of a diffracted beam was derived.
The crystal gyrotropy has been found to affect significantly the change in the amplitude profile of the diffracted light at
ultrasound frequencies of f ∼ 102–103 MHz. The maximum diffraction efficiency in the gyrotropic medium is shown to be reached at a certain ratio between the divergences,
ultrasound intensity, and specific gyration of the crystal.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 370–374, May–June, 2000. 相似文献