Incoherent Photon Research Articles

Generation of incoherent mid-infrared photon echoes with parametrically downconverted light

We present a demonstration of mid-infrared photon echoes generated with parametrically downconverted incoherent light. The photon echoes generated in this way enable one to study the dynamics of vibrations in the 1.5-4.0-microm wavelength region with subpicosecond time resolution.

Quantized motion of atoms in a magneto-optical potential under coherent population trapping in high-intensity laser fields

We study theoretically the quantized motion of previously cooled atoms in a one-dimensional magneto-optical potential under coherent population trapping (CPT) conditions. We consider atoms with a transition interacting with a lin lin laser field and a static uniform magnetic field in the high-intensity limit. It is shown that if the Rabi frequency is greater than the Zeeman splitting, Doppler shift, natural width and detuning, then atoms are captured in the long-lived CPT state while the excited-state population is small. We do not take into account the incoherent photon scattering and describe the atomic motion by the Schrodinger equation. The oscillation frequency, oscillation damping time and localization size are obtained for atoms moving near the bottom of potential wells in a harmonic approximation. Narrowing of the vibrational spectral lines due to the CPT effect is predicted.

Difference between Coherent-Pulse and Incoherent-Pulse Photon Echoes in Non-Markovian Behavior

By using stochastic theory, we clarified the difference between coherent and incoherent two-pulse photon echoes from the viewpoint of non-Markovian behavior. At the slow modulation limit, the incoherent two-pulse echo was found to exhibit an exp (- c t 2 ) dependence which is in contrast with the exp (- c t 3 ) dependence in the coherent two-pulse echo.

Optical dephasing of organic dye molecules doped in cross-linked polyvinyl alcohol derivatives: Incoherent photon echo and hole-burning studies

Optical dephasing of the zero-phonon line (ZPL) of organic dye molecules doped in polyvinyl alcohol (PVA) and several cross-linked PVA derivatives was studied by using the incoherent photon echoes and the photophysical persistent hole-burning. It was found in the incoherent photon echo measurements that optical dephasing time of the ZPL increases with increasing the length of a cross-linker introduced to the PVA backbone. The difference in the temperature dependence of the dephasing time was also observed between a dye doped in PVA with and without the cross-link. When a longer cross-linker was introduced, the phonon sideband component in the incoherent photon echo signal became dominant in contrast to that in PVA with a relatively short cross-linker, while the dephasing time of the ZPL was still longer than that in PVA without the cross-link. Hole-burning studies showed that the phonon sideband spectrum of a dye doped in the cross-linked PVAs is essentially similar to that in PVA. However, the depth of the zero-phonon hole burnt with the same burning power was found to depend on the PVA hosts with the cross-linkers. These our findings suggest that the introduced cross-link does not alter the electron–phonon coupling modes or pseudo-local mode, but it drastically reduces the effect of the two-level tunneling systems in PVA on the optical dephasing of a doped dye. As a result, the dephasing time of the dye in the cross-linked PVAs becomes longer than that in PVA without the cross-link. The decrease of the optical dephasing by introducing the cross-link can be interpreted by assuming a void space in PVA, which is created near to the cross-linker. In addition, absorption and fluorescence spectra in these systems were measured, which imply the occurrence of weak dye–dye interaction when the dye is doped in PVA with a much longer cross-linker.

Nanosecond spectral diffusion and optical dephasing in organic glasses over a wide temperature range: incoherent photon echo study of resorufin in D- and D 6-ethanol

Incoherent photon echoes (IPE) decay curve of two differently deuterated ethanol glasses: resorufin in d-ethanol (r/d-e) and resorufin in d 6-ethanol (r/d 6-e) have been measured in wide temperature interval (1.7–35 K). At low temperatures the difference in decay times between results of IPE and two-pulse picosecond photon echoes (2PE) were observed and attributed to nanosecond spectral diffusion (SD). The T-dependence of the SD contribution in IPE data was defined and analyzed using Bai-Fayer theory. IPE high temperature results have shown that high-temperature dephasing in r/d-e is caused mainly by interaction with single low frequency mode (LFM). LFM dephasing was analyzed using Osad'ko nonperturbative dynamical theory. The difference in temperature dependencies of dephasing time between r/d-e and r/d 6-e was observed: the deuteration influenced both on LFM and two-level systems (TLS) contribution to dephasing.

Elastic and inelastic scattering of photons in the X-ray energy region

Coherent and incoherent photon scattering cross sections for elements C, Si, V, Fe, Cu, Zn, Mo, Au and Pb and some alloy samples have been measured at E = 34.6 keV. Experimental results are compared with normalised integrated cross sections based on form-factor and the incoherent scattering function approximations. Experimental results are in general higher than theory. Further measurements on coherent and incoherent scattering cross sections need to be performed in the X-ray energy region. Also the exact calculations of differential coherent scattering cross sections need to be done in this energy range.

Tissue characterization and imaging using photon density waves

The optical properties of brain tissues have been evaluated by measuring the phase velocity and attenuation of harmonically modulated light. The phase velocity for photon density waves at 650-nm wavelength has been found to be in the range of 5 to 12% of the corresponding velocity in a nonscattering medium, and the optical penetration depth was in the range 2.9 to 5.2 mm. These results are used to predictthe resolution of optical imaging of deep tissue structures by diffusely propagating incoherent photons. The results indicate that structures of a few millimeters in linear dimension can be identified at 10 mm depth provided that proper wavelength and time resolution are selected. This depth can possibly be enlarged to 30 mm in the case of tissues with very low scattering such as in the case of the neonatal human brain.

Pulsar magnetospheres

The energy loss from the neutron star - as inferred from the secular increase in rotation period - is much greater than that emitted in either the radio or the other observed wavelengths. A primary motivation of magnetospheric theory is to trace the mode in which this energy and the associated angular momentum are in fact carried off from active pulsars. This review concentrates on the special case in which the magnetic and rotation axes are aligned. Electrons emitted from the polar caps are accelerated to highly relativistic energies by the electric force and simultaneously pick up angular momentum from the magnetic torque. Some process of angular momentum dissipation occurring beyond the light-cylinder is then required, both to yield the continuous spin-down of the star, and also to allow the electrons to cross magnetic field lines and so complete their circuits back to the star. Within the framework of classical physics, this could occur if most of the spin-down energy is lost through incoherent photon emission in an equatorial domain beyond the lightcylinder, but this would generate y-radiation far in excess of that observed. Transport away of the angular momentum via a relativistic wind requires the generation of a quasi-neutral plasma. Gamma-rays emitted by outflowing electrons will produce electron-positron pairs in the strong magnetic field near the star, and highly energetic electrons returning to the star may also generate a mixed plasma by pair production or by surface spallation. Coupling with the circulating primary electron current may then ensure that the dominant angular momentum loss is via the wind rather than through photon emission.

Host-dependent optical dephasing of dye molecules doped in cross-linked polyvinyl alcohols

Host-dependent optical dephasing of the zero-phonon line of two organic dye molecules doped in several cross-linked polyvinyl alcohol (PVA) derivatives was studied by using an incoherent photon echo technique. It was found that the optical dephasing time of the zero-phonon line increases with increasing the length of the cross-link introduced to the PVA backbone. Our results indicate that, by the introduction of the cross-link, the effect of the two-level tunneling system in PVA on optical dephasing of a doped dye is greatly reduced and the dephasing time of the dye becomes longer than that in the PVA without the cross-link. The decrease of the optical dephasing can be interpreted by assuming a void space in PVA, which is created near to an introduced cross-linker.

Ultrafast dephasing of Resorufin in d-ethanol glass from 17 to 40 K studied by incoherent photon echo

The temperature dependence of the electronic dephasing of Resorufin in d-ethanol glass was measured from 1.7 to 40 K by incoherent photon echo (IPE) techniques. At T = 8–11 K good agreement between IPE and two-pulse picosecond photon echo (PPE) results was observed. For T 11 K confirm the hypothesis that high-temperature dephasing in this system is due mainly to interaction with a pseudolocal mode.

The role of pionic currents in gamma emission during nuclear encounters

A review of experimental data on Nucleus-Nucleus-Gamma reactions is given. Spectra display an exponential shape above 30 MeV, with an almost linear variation of the exponential parameter with incident beam energy. The laboratory angular distributions show strong forward peaking, as well as a remarkable insensitivity to the mass ratios of target and projectile. Transformed into the nucleon-nucleon center of mass, these angular distributions display forward backward symmetry. They are mostly isotropic, with a slight admixture of a dipole component. In first approximation, the intensity of the spectra appear to be proportional to the number of first nucleon-nucleon collisions, which leads to a simple scaling law. Exclusive measurements display an interesting correlation between the hardness of the spectra and the centrality of the collision. Experimental results put stringent constraints on theoretical models. The scaling laws appear to contradict the prediction of collective models where both nuclei behave like entities. The angular distributions do not seem to be easily reconciled with emission by thermal sources. Semi-classical dynamical calculations of the BUU or Landau-Vlassov type, where the collision term is the source of incoherent photon emission, have been used extensively to reproduce the experimental results. These calculations were able to reproduce most of the experimental features. Photon emission in Nucleus-Nucleus collisions is, thus, intimately related to that occuring in the elementary n-p reaction. Recent measurements and calculations show that most of the photon production is, in this case, related to the charged pion exchange between the two nucleons. Therefore, Nucleus-Nucleus collisions may be a unique probe of the exchange currents in hot and dense nuclear matter.

Vibrointerference and modulation of Mössbauer radiation

Vibrointerference was studied earlier as a method to obtain interference patterns from incoherent photon sources. This paper proposes a new approach to the effect as an ultrasound modulation with spatially dependent parameters. One possible application is also proposed.

Ultrafast Dephasing and Incoherent Light Photon Echoes in Organic Amorphous Systems

Incoherent light photon echoes were observed in organic amorphous systems (cresyl violet in polyvinyl alcohol and 1,4-dihydroxyanthraquinone in polymethacrylic acid) by using temporally-incoherent nanosecond laser pulses. It was found that an echo decay curve of an organic amorphous system is composed of a sharp peak which decays very rapidly and a slowly decaying wing at the tail. We show that the persistent hole burning (PHB) spectra were reproduced by the Fourier-cosine transforms of the echo decay curves. We claim that in general, we must take into account the multi-level feature of the system in order to explain ultrafast dephasing at very low temperatures.

Optical dephasing in glasses: Theoretical comparison of the incoherent photon echo, accumulated grating echo, and two-pulse photon echo experiments

We present a detailed theoretical analysis of three nonlinear optical dephasing experiments, the incoherent photon echo, the accumulated grating echo, and the two-pulse photon echo. It has been believed previously that these three experiments provide the same information about optical dephasing, and therefore about a system's dynamics. In systems such as chromophores in glasses, proteins, liquids, or complex crystals, in which spectral diffusion (slow time scale energy fluctuations) as well as homogeneousdephasing (fast time scale energy fluctuations) occur, it is proven that these techniques are not equivalent. While the two-pulse photon echo measures the homogeneous dephasing, the other two techniques are influenced by spectral diffusion. In general, the incoherent echo and the accumulated grating echo will measure dephasing rates which are faster than the two-pulse photon echo. The differences among the methods are calculated using a standard two-level system model of glasses. It is found that the differences depend on factors such as the pulse duration in the incoherent echo and the triplet life time in the accumulated grating echo. We also demonstrate that a combination of techiques can be used to map out the broad distribution of relaxation rates which occur in glasses and many other complex systems.

Photonuclear and atomic cross sections of 27Al between 3 and 38 MeV.

The total cross section for photon absorption of Al was measured for energies between 3 and 38 MeV with a el-ray spectrometer consisting of a liquid deuterium target viewed by a photoneutron time-of-flight detector. Corrections to the observed total cross section for background electromagnetic processes in the absorber were computed by a Monte Carlo method. Between 5 and 8 MeV where the photonuclear cross section sigma/sub N/ is negligible and the uncertainty in the measurements is small, values of the atomic cross section sigma/sub Z/ calculated by others systematically exceed the measured values by 0.7%. In this energy interval sigma/sub Z/ is mainly due to incoherent photon scattering by atomic electrons. Nonrelativistic atomic form factors and estimated radiative corrections used in calculating the tabulated incoherent scattering cross sections introduced enough uncertainty to justify decreasing sigma/sub incoh/ by 0.87% to bring sigma/sub Z/ into agreement with experiment. Correcting this discrepancy causes the integral between 10 and 38 MeV of sigma/sub N/, which has a maximum value of about 5% of sigma/sub Z/, to increase by 18% to 500 MeV mb. We conclude that the giant dipole resonance of /sup 27/Al has a strength of 1.24 classical sum rule units.

Quantum fluctuations for two-level atoms in a high-Q cavity with a spatially varying field mode.

An extension of the quantum theory of the atom-field interaction within a high-finesse resonator is made to include spatial variations of the field mode in the limit of small cavity decay rate. The two particular examples of a Gaussian mode field in a ring cavity and a plane-wave field in a standing-wave interferometer are presented to illustrate the method. Analytic expressions are obtained for the incoherent intensity and photon correlations of the transmitted field. In qualitative terms, effects such as sub-Poissonian photon statistics predicted by the plane-wave theory in a ring cavity are preserved. In either the weak-field or dispersive limit the results of the plane-wave theory in a ring cavity are recovered independent of the form of the spatial dependence of the cavity mode.

Rapid thermal nitridation of thin thermal silicon dioxide films

The electrical characteristics of thin nitrided thermal silicon dioxide films prepared by a new rapid thermal process are described. This process is performed in a controlled gas ambient under an incoherent photon flux with a duration typically less than 60 s. It allows the incorporation of a controlled nitride layer in the bulk (oxinitride), on the surface, or at the silicon interface of the oxide. Gate dielectrics with superior electrical and chemical properties have been obtained. Applications in metal-oxide-semiconductor integrated circuit technologies are suggested.

Note on incoherent photon scattering by a statistical atom

The incoherent X-ray scattering by a statistical atom is studied for the screening function restored by using the experimental energy distribution of atomic electrons.

A Refinement of the Mollwo‐Ivey Rule for F‐Centres in Alkali Halides

AbstractIt is found that the simple formula , where A = 328, B = 9.3118, and a = 1/x the nearest‐neighbour distance in Bohr radii, is a very good fit for the detailed variation of the F‐centre peak absorption energy, E (in Ryd), with a, for the 16 alkali halides with NaCl structure, excluding CsF. The first term arises from incoherent photon scattering leading to electronic level transitions. The second term is a diffraction term, arising from the coherent scattering of photons from relaxed ionic aggregates around F‐centers separated on the average by distances of the order of optical wavelengths.

Unified theory for estimating frequency-of-occurrence laws and optical objects

What is the optimum estimator for optical objects and other occurrence-rate distributions, such as for droplet size? Any contender must obey positivity: optical objects are nonnegative energy sources, and occurrence rates cannot be negative. Maximum entropy has been a contender, but it occurs in at least four forms—used by Jaynes, Burg, Kullbach, and Kikuchi and Soffer. Is any of these the correct one? And, if so, under what conditions? Our viewpoint is that a higher principle should be used that becomes one of the entropy forms, or some other form, under different conditions of prior knowledge. Such a principle is maximum likelihood (ML). We have derived a general ML estimator for spatially incoherent photon or electron objects, using a conventional statistical-physics approach. Results are also applied to other occurrence-rate problems, in particular that of water-droplet or snowflake size in a cloud. The ML estimator accommodates all physical and statistical prior knowledge about the unknown that may be known to the user. The physical knowledge for the optical problem includes the taking conditions (exposure time, pixel-cell size), coherence conditions, and either the Bose–Einstein or the Fermi–Dirac nature of the quanta involved. Statistical knowledge enters through an object-class law on joint intensities, or on occurrences, across the unknown. Specific forms of statistical knowledge are assumed in turn: strong, empirical, none at all, and negative. The resulting ML estimators are maximum (Shannon) entropy, maximum Kikuchi–Soffer entropy, minimum entropy, maximum or minimum cross entropy, maximum Burg or weighted-Burg entropy, minimum photon-site entropy, maximum empirical entropy, or no estimator at all. Other estimators exist as well, depending on the prior knowledge at hand. It behooves the user to define the prior knowledge that most accurately and completely defines his problem.