The internal energy of small ammonia clusters in a supersonic beam and after scattering off LiF(100)

The photoionization efficiency (PIE) of neutral ammonia clusters is studied as a function of photon energy. From these curves the internal energies of clusters in the incident supersonic beam and of clusters surviving after scattering off a LiF(100) surface are derived. A supersonic expansion of ammonia seeded in He produces small clusters of various size but with uniform kinetic energy of about 285 meV per monomer molecule. The mass distribution of clusters in the jet and of the scattered particles is measured in a reflecting time-of-flight mass spectrometer by single photon photoionization using vacuum ultraviolet (VUV) laser radiation tunable between and . In the incident beam the internal energies of clusters up to n = 15 do not vary significantly and amount to an average of about . After scattering off LiF(100) the internal energy of clusters up to n = 4 increases with fragment size and amounts to about half a monomer binding energy. Received 18 October 1999 and Received in final form 10 December 1999     

ac Stark effect for a two-level atom in a squeezed vacuum via a two-photon process

The nondegenerate two-photon interaction of a two-level atom with a broadband multimode squeezed vacuum is investigated. We find that in the two-photon process the squeezed vacuum has a driving effect on the atom which can lead to an ac Stark effect when the average photon number of the squeezed vacuum is larger than a critical value. Received: 2 February 1999 / Received in final form: 20 April 1999     

Photon-electron scattering taking vacuum energy into account

We deal with photon-electron scattering between the two uncharged conducting parallel plates. The electromagnetic vacuum field between the two plates is defined by the configuration of space and also interacts with the electrons. We first deal with the relevant operators for the electron and photon fields and with the Feynman propagator. We compute theS-matrix for photon-electron scattering, taking into account the influence of the vacuum field. The computed photon-electron scattering cross section also manifests the influence of the vacuum field. We give an example for low-energy scattering of the influence of the vacuum field upon the scattering cross section.     

Influence of vacuum energy on scattering

We deal with photon-electron scattering which occurs between two uncharged conducting parallel plates moving away from each other at a constant velocity. The electromagnetic vacuum field between two plates is defined by the configuration of space and also interacts with the electrons. We show the relevant operators for both the electron and photon fields and the computation of the corresponding Feynman propagator,S-matrix, and scattering cross section, taking into account the influence of the changeable vacuum field. Correction terms in the computedS-matrix and scattering cross section manifest the influence of the changeable vacuum field. We analyze an example for low-energy scattering of the influence of the changeable vacuum field upon the scattering cross section.     

Photon-number dependent cavity vacuum induced transparency and single photon separation

We investigate photon-number dependent cavity vacuum induced transparency and magneto-optical rotation (MOR) in a cavity quantum electrodynamics system, which consists of two cavities and an ensemble of Λ-type atoms. We demonstrate that the probe photon coupled into one cavity can be transferred to the mode of another cavity via coherent Raman scattering. The transmission, the phase shift, as well as the vacuum Rabi splitting therefore strongly depend upon the probe photon number coupled into the cavity. The photon number dependent cavity vacuum induced transparency can be extended into four-level tripod atoms, leading to photon-number dependent MOR. This can be used to separate the single photon from higher photon number components in the direction of polarization and create a deterministic single photon source.     

Inelastic light scattering by dipolar excitons

The cross section for inelastic light scattering by a system of spatially indirect excitons is calculated. It is shown that there are two resonant scattering channels, one related to the transitions via the vacuum and the other via the two-exciton states of the crystal, and their contributions to the scattering amplitude cancel each other. As a result, there is no resonance enhancement of light scattering by excitons for photon energies in the vicinity of the band gap.     

Inclusive Single- and Dijet Rates in Next-to-Leading Order QCD for γ*p and γ*γ Collisions

We present one- and two-jet inclusive cross sections for γ*γ scattering and virtual photoproduction in ep collisions. The hard cross sections are calculated in next-to-leading order QCD. Soft and collinear singularities are extracted using the phase-space-slicing method. The initial state singularity of the virtual photon depends logarithmically its’ virtuality. This logarithm is large and has to be absorbed into the parton distribution function of the virtual photon. We define for this purpose an factorization scheme similar to the real photon case. We numerically study the dependence of the inclusive cross sections on the transverse energies and rapidities of the outgoing jets and on the photon virtuality. The ratio of the resolved to the direct cross section in ep collisions is compared to ZEUS data.     

Frequency up-converted radiation from a cavity moving in vacuum

We calculate the photon emission of a high finesse cavity moving in vacuum. The cavity is treated as an open system. The field initially in the vacuum state accumulates a dephasing depending on the mirrors motion when bouncing back and forth inside the cavity. The dephasing is not linearized in our calculation, so that qualitatively new effects like pulse shaping in the time domain and frequency up-conversion in the spectrum are found. Furthermore we predict the existence of a threshold above which the system should show self-sustained oscillations. Received: 10 December 1997 / Received in final form: 27 March 1998 / Accepted: 27 March 1998     

Windowless transition between atmospheric pressure and high vacuum via differential pumping for synchrotron radiation applications

A differential pump assembly is introduced which can provide a windowless transition between the full atmospheric pressure of an in‐air sample environment and the high‐vacuum region of a synchrotron radiation beamline, while providing a clear aperture of approximately 1 mm to pass through the X‐ray beam from a modern third‐generation synchrotron radiation source. This novel pump assembly is meant to be used as a substitute for an exit vacuum window on synchrotron beamlines, where the existence of such a window would negatively impact the coherent nature of the X‐ray beam or would introduce parasitic scattering, distorting weak scattering signals from samples under study. It is found that the length of beam pipe necessary to reduce atmospheric pressure to below 10 mbar is only about 130 mm, making the expected photon transmission for hard X‐rays through this pipe competitive with that of a regular Be beamline window. This result is due to turbulent flow dominating the first pumping stage, providing a mechanism of strong gas conductance limitation, which is further enhanced by introducing artificial surface roughness in the pipe. Successive reduction of pressure through the transitional flow regime into the high‐vacuum region is accomplished over a length of several meters, using beam pipes of increasing diameter. While the pump assembly has not been tested with X‐rays, possible applications are discussed in the context of coherent and small‐angle scattering.     

Generation of a displaced qubit and entangled displaced photon state via conditional measurement and their properties

We study optical schemes for generating both a displaced photon and a displaced qubit via conditional measurement. Combining one mode prepared in different microscopic states (one-mode qubit, single photon, vacuum state) and another mode in macroscopic states (coherent state, single photon added coherent state), a conditional state in the other output mode exhibits properties of a superposition of the displaced vacuum and a single photon. We propose to use the displaced qubit and entangled states composed of the displaced photon as components for quantum information processing. Basic states of such a qubit are distinguishable from each other with high fidelity. We show that the qubit reveals both microscopic and macroscopic properties. Entangled displaced states with a coherent phase as an additional degree of freedom are introduced. We show that additional degree of freedom enables to implement complete Bell state measurement of the entangled displaced photon states.     

Entanglement dynamics for a solid polariton system at zero and finite temperatures

The dynamics of the entanglement for a solid polariton system is investigated. The polariton system is a photon-phonon complex and its time-dependent characteristic function in the Wigner representation for the system is obtained analytically. It is found that when the photon field is initially prepared in the squeezed vacuum state, and the phonon in the thermal state, the polariton system can evolve into a two-mode Gaussian mixed state. The entanglement between photon and phonon turns out to be apparently dependent on the squeezing parameter and exhibits a critical behavior with respect to the temperature.     

Experimental conditions required to verify the existence of a photon medium

If a scalar field incorporating a photon/environment interaction exists in nature, it should be possible to create a photon medium by focusing intense laser beams either in a vacuum or in a plasma. Such a medium should sustain many of the non-linear optical effects observable in material media. Techniques are proposed for verifying the existence of a photon medium via its effect on both the velocity of light and the scattering of light by light in intense laser beams.     

Dynamics of superhorizon photons during inflation with vacuum polarization

We study asymptotic dynamics of photons propagating in the polarized vacuum of a locally de Sitter Universe. The origin of the vacuum polarization is fluctuations of a massless, minimally coupled, scalar, which we model by the one-loop vacuum polarization tensor of scalar electrodynamics. We show that late time dynamics of the electric field on superhorizon scales approaches that of an Airy oscillator. The magnetic field amplitude, on the other hand, asymptotically approaches a nonvanishing constant (plus an exponentially small oscillatory component), which is suppressed with respect to the initial (vacuum) amplitude. This implies that the asymptotic photon dynamics is more intricate than that of a massive photon obeying the local Proca equation.     

Scaling violation in γγ scattering

An unorthodox model is examined which predicts that scaling violations in structure functions are related to properties of the photon vacuum polarization amplitude. The relationship is approximate, but very useful. It reproduces the leading QCD prediction in all cases, and allows, as for instance in γγ scattering, to fill up on what QCD cannot say by itself. There is a simple formula for the total γγ cross-section, valid for all values of the photon mass. Data frome ⁺ e^? annihilation can be fed into it to obtain a fit to the measured photon structure function. The PLUTO data are not all difficult to reproduce.     

Vacuum-stimulated raman scattering based on adiabatic passage in a high-finesse optical cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counterintuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a subnatural linewidth. The results are in excellent agreement with numerical simulations.     

Electron transmission through organized organic thin films studied by discrete initial electron kinetic energies

Synchrotron radiation (SR) pulses are used to eject electrons from a gold substrate covered with organized organic thin films (OOTF) in order to investigate their transmission probability through the OOTF as a function of the electron initial kinetic energy. By variation of the SR photon energy within a few eV above the Au-4f binding energy levels we controlled the initial kinetic energy of the substrate electrons. The observed oscillations in the transmission probability for porphyrin-based films as a function of the kinetic energy is argued to be due to effects of band structure above the vacuum level in the well-ordered molecular adsorbate. We also present valence photoemission spectra (PES) of different type OOTF and demonstrate how their coverage of the substrate affects the PES. Received 24 July 1998     

Radiative corrections to very high energy electron-proton scattering

A “leading log” analysis of radiative corrections to inclusive ep scattering at HERA energies is presented. Neutral current weak interactions are considered at the level of the Born cross section as well as of the modifications of vertex and vacuum polarization parts. The leading log approximation has been also improved in the single hard and multiple soft photon emission by appropriate kinematical considerations. Some numerical results are presented for polarized electron and positron beams.     

Induced photon emission from quark jets in ultrarelativistic heavy-ion collisions

We study the induced photon bremsstrahlung from a fast quark produced in AA collisions due to multiple scattering in quark-gluon plasma. For RHIC and LHC conditions, the induced photon spectrum is sharply peaked at a photon energy close to the initial quark energy. In this region, the contribution of the induced radiation to the photon fragmentation function exceeds the ordinary vacuum radiation. Contrary to previous analyses [4–7], our results show that, at RHIC and LHC energies, the final-state interaction effects in quark-gluon plasma do not suppress the direct photon production and may even enhance it at p _T ～5–15 GeV.     

Random lasing in porous scattering medium

The spectrum behavior evolution and the threshold of random lasing depending on the way of photon walk randomization in an active random medium were investigated. The following three ways of photon walk randomization were implemented: multiple light scattering by corundum and silica particles embedded into a solid polymer solution of dye (astrafloxin), multiple light reflection at sub-millimeter extensive air pores (mean diameter 200 μm) produced in the medium, and the combined action of both these effects. The most effective lasing is observed in the case of an active medium with air pores and scattering particles in the interpore space. Such a combined porous scattering medium acts as a network of dielectric waveguides transmitting effectively the random light. This spatial structure of the random active medium significantly increases the photon path in the medium, thereby promoting photon multiplication due to stimulated emission. In this combined medium the random lasing reveals the narrowest spectrum, the lowest threshold, and the highest density of spectral energy in the spectrum maximum.