Possible experimental test of photon non-locality from a one-photon state

An experimental test of photon non-locality from a one-photon state and of the wave packet reduction in a one-photon state is proposed. It could be tested that the correlation between both arms of the arrangement in the one-photon state remains unchanged when the first arm is modified after both photon wave packets have separated.     

Study of sequential two photon absorption and conduction band electrons absorption in ZnSe

Using the Z-scan technique and pump–probe technique with 130 fs laser pulses at 800 nm, we verify that an intraband one-photon absorption follows the interband two photon absorption. Particularly, we find that there is an intraband relaxation interspersed between these two absorption processes for some of the conduction band electrons but not all of them. In this study, we measure the interband two photon absorption coefficient and the absorptive cross sections associated with both excitation pathways within the conduction band. In addition, we estimate the time for relaxation of electrons within the conduction band to be 250 fs.     

Generation of one-photon states by a quantum dot

A technique for preparation of a one-photon wave packet through action of a classical electromagnetic field on a semiconducting quantum dot is proposed. We demonstrate that the Coulomb repulsion between charge carriers allows one to select the frequency, amplitude, and duration of an electromagnetic pulse so that one electron will transfer from an upper size-quantized level of the valence band to a lower size-quantized level of the conduction band with a probability close to unity. As a result of radiative recombination of the produced electron-hole pair, exactly one photon is emitted (a one-photon wave packet). This source of one-photon states can be used in quantum systems of data transmission and in quantum computers. Zh. éksp. Teor. Fiz. 112, 1257–1272 (October 1997)     

Pure spin current from one-photon absorption of linearly polarized light in noncentrosymmetric semiconductors

We show that one-photon absorption of linearly polarized light should produce pure spin currents in noncentrosymmetric semiconductors, including even bulk GaAs. We present 14x14 k.p model calculations of the effect in GaAs, including strain, and pseudopotential calculations of the effect in wurtzite CdSe.     

Two-photon absorption of optical and x-ray quanta

Two-photon absorption of an optical (laser) and an x-ray quantum is considered within the context of the Born approximation. A simple expression relating the two-photon and one-photon photoionization absorption coefficients is obtained. If the upper state is one of the conduction bands of a solid, the two-photon absorption coefficient is shown to peak at points in the zone for which the curvature of the band is a maximum. Numerical estimates show that with a 100 kW Nd laser, the intensity of the two-photon absorption process is a few percent of that of the one-photon process.     

Determination of Г3 valence band in CuCl by two-photon absorption

We present the first two-photon measurements of higher band to band transitions in CuCl far beyond the well-known exciton transitions. Our measurements allow to locate the Г^v₃ valence band. This band cannot be observed in one-photon absorption in a transition to the lowest conduction band of Г^c₁ symmetry. Our assignment, which we confirm by the observed polarization dependence, should be used to reinterpret recent one-photon data.     

Shift photocurrent induced by two-quantum transitions

A theory of the shift current induced by direct two-photon and indirect one-photon absorption is developed for noncentrosymmetric crystals. A formula is derived for the microscopic shifts of Bloch electrons induced by two-quantum processes. It is shown that the ratio of the two-photon photocurrent at the photon frequency ω to the photocurrent induced by direct one-photon transitions at the photon frequency 2ω, as compared to the corresponding absorption-rate ratio, contains a large factor {ie152-1}ω/(2{ie152-2}ω − E _g), where E _g is the bandgap; i.e., these photocurrent can be comparable in order of magnitude. For crystals of T _d symmetry, the photocurrents induced by one- and two-photon absorption are compared in terms of polarization dependence.     

Excitonic molecule in semiconductors by two-photon absorption

Direct creation of bi-exciton states by two-photon absorption in direct gap semiconductors is investigated theoretically. A numerical application to the case of CuCl shows that the two-photon absorption coefficient for bi-excitonic transitions is larger than that for two-photon interband transitions by three orders of magnitude. It becomes comparable to that for one-photon excitonic transitions for available laser intensities. The main contribution to this enhancement of the absorption coefficient for the transitions to the bi-exciton states is found to be from the resonance effect.     

Total teleportation of zero- and one-photon entangled states in running waves

Inspired by a recent paper [2002 J. Opt. B 4 316] we present an alternative scheme to teleport an entanglement of zero- and one-photon states of a running-wave field. The scheme employs only linear optical elements plus single-photon sources and detectors.     

Quantitative differentiation of dyes with overlapping one-photon spectra by femtosecond pulse-shaping

We demonstrate that DiI and rhodamine B, which are not easily distinguishable to one-photon measurements, can be differentiated and in fact quantified in mixture via tailored two-photon excitation pulses found by a genetic algorithm (GA). A nearly three-fold difference in the ratio of two-photon fluorescence of the two dyes is achieved, without a drop in signal of the favored fluorophore. Implementing an acousto-optic interferometer, we were able to prove that the mechanism of discrimination is second-harmonic tuning by the phase-shaped pulses to the relative maxima and minima of these cross-sections.     

“Negative” absorption and “negative” emission in nonlinear optics

The nonlinear susceptibilities X³ (ω₂ = ω₁ ? ω₁ + ω₂) calculated for stimulated Raman scattering (SRS) and two- photon absorption (TPA) under the condition of one-photon resonance in the case of a multilevel system with broad overlapping absorption bands (corresponding to polyatomic molecules) are discussed. Spectra of Im X³ with changed sign in some spectral regions are shown. The result is connected with a disbalance of the system, due to the large relaxation constants.     

Total teleportation of zero- and one-photon entangled states in running waves

Inspired by a recent paper [2002 {\it J. Opt. B {\bf 4 316] we present an alternative scheme to teleport an entanglement of zero- and one-photon states of a running-wave field. The scheme employs only linear optical elements plus single-photon sources and detectors.     

First observation of two-electron one-photon transitions in single-photon K-shell double ionization

Experimental evidence for the correlated two-electron one-photon transitions (1s(-2)→2s(-1)2p(-1)) following single-photon K-shell double ionization is reported. The double K-shell vacancy states in solid Mg, Al, and Si were produced by means of monochromatized synchrotron radiation, and the two-electron one-photon radiative transitions were observed by using a wavelength dispersive spectrometer. The two-electron one-photon transition energies and the branching ratios of the radiative one-electron to two-electron transitions were determined and compared to available perturbation theory predictions and configuration interaction calculations.     

The Dynamic Behaviour Analysis of Up－Conversion Luminescence in ErP_5O_（14） Glass

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Comparison of the Raman detection limit for IRS- and CARS-spectroscopy at excitation near molecular one-photon resonance

The nonlinear Raman methods IRS and CARS are compared according to the signal detectability at excitation of molecules under the condition of one-photon resonance. At one photon resonance it is the background contribution resulting from the scattering molecules themselves that determines the maximum attainable signal to noise ratio. These contributions acting for IRS and CARS respectively are compared. The essential difference between IRS and CARS results from a 3rd order saturation contribution to IRS, which may mask the IRS Raman signal near exact resonance while it does not contribute to CARS. This gives to CARS the preference before IRS at resonance excitation. The situation for IRS with respect to background is similar to that of spontaneous Raman scattering, where the resonance fluorescence — corresponding to the saturation contribution at IRS — masks the resonance Raman signal.     

Fluorescence intensity and anisotropy decays of the DNA stain Hoechst 33342 resulting from one-photon and two-photon excitation

We examined the steady-state and time-resolved fluorescence spectral properties of the DNA stain Hoechst 33342 for one-photon (OPE) and two-photon (TPE) excitation. Hoechst 33342 was found to display a large cross section for two-photon excitation within the fundamental wavelength range of pyridine 2 and rhodamine 6G dye lasers, 690 to 770 and 560 to 630 nm, respectively. The time-resolved measurements show that intensity decays are similar for OPE- and TPE. The anisotropy decay measurements of Hoechst 33342 in ethanol revealed the same correlation times for TPE as observed for OPE. However, the zero-time anisotropies recovered from anisotropy decay measurements are 1.4-fold higher for TPE than for OPE. The anisotropy spectra of Hoechst 33342 were examined in glycerol at ?20°C, revealing limiting values close to the theoretical limits for OPE (0.4) and TPE (0.57). The steady-state anisotropy for OPE decreases in the shorter-wavelength region (R6G dye laser, 280–315 nm), but the two-photon anisotropy for 560 to 630-nm excitation remains as high as in the long-wavelength region (690–770 nm). This result suggests that one-photon absorption is due to two electronic, but only one transition contributes to the two-photon absorption over the wavelength range from 580 to 770 nm. Our demonstration of these favorable two-photon properties for Hoechst 33342, and the high photostability of the dye reported by other laboratories, suggests that this dye will be valuable for time-resolved studies of DNA with TPE and for two-photon fluorescence microscopy.     

薄原子蒸汽膜的双光子光谱及Dicke窄化

薄原子蒸汽膜的单光子Dcike窄化吸收光谱可以拓展到双光子情形，以级联三能级系统为例,从理论上得到了亚多普勒结构的双光子吸收光谱，其线型表现出和单光子过程相似的与膜厚和探测光波长的比值(L/λ)相关的周期性.当L/λ=(2n+1)/2(膜厚为半波长的奇数倍)时，吸收谱线窄化现象明显.当L/λ=2n/2(膜厚为半波长的偶数倍)时，单光子情形的谱线窄化现象消失，而双光子情形的谱线仍表现为亚多普勒结构，尤其在异侧入射的情形下，可以获得极窄的双光子谱线结构. 这种结构来自原子与腔壁碰撞的消激发效应和双光子过程的抽运-探测机制的贡献. 关键词： 薄原子蒸汽膜 双光子光谱 Dicke窄化     

Diffraction of entangled photon pairs by ultrasonic waves

In this paper, we have presented and established a new theoretical formulation of photon optics based on photon path and Feynman path integral idea. We have used Feynman path integral approach to discuss Fraunhofer, Fresnel diffraction of single photon and entangled photon pairs by ultrasonic wave and obtained the following results: i) quantum state and probability distribution of single photon and entangled photon pairs by Fraunhofer and Fresnel ultrasonic diffraction, ii) oblique incidence Raman-Nath and Bragg diffraction conditions, iii) total correlation state and its probability distribution. Our calculation results are in agreement with the experiment results. Comparing one-photon and two-photon diffraction effects by ultrasonic waves, we have found that two-photon diffraction by ultrasonic waves is also a sub-wavelength diffraction.     

EFATOM two-detector one-photon emission gamma tomograph

The EFATOM two-detector one-photon emission computer tomograph, which is intended for radionuclide diagnostics of the internal organs and systems in the human body, has been designed and tested. A schematic diagram of its software package and detection units is represented. The results of its technical tests are presented. The characteristics of the EFATOM gamma tomograph are compared with its foreign analogs.