43 research outputs found
Optical Sensors Using Stimulated Brillouin Scattering
A method for enhancing a sensitivity of an optical sensor having an optical cavity counter-propagates beams of pump light within the optical cavity to produce scattered light based on Stimulated Brillouin Scattering (SBS). The properties of the pump light are selected to generate fast-light conditions for the scattered light, such that the scattered light includes counter-propagating beams of fast light. The method prevents the pump light from resonating within the optical cavity, while allowing the scattered light to resonate within the optical cavity. At least portions of the scattered light are interfered outside of the optical cavity to produce a beat note for a measurement of the optical sensor. The disclosed method is particularly applicable to optical gyroscopes
Coherent Control of Isotope Separation in HD+ Photodissociation by Strong Fields
The photodissociation of the HD+ molecular ion in intense short- pulsed
linearly polarized laser fields is studied using a time- dependent wave-packet
approach where molecular rotation is fully included. We show that applying a
coherent superposition of the fundamental radiation with its second harmonic
can lead to asymmetries in the fragment angular distributions, with significant
differences between the hydrogen and deuterium distributions in the long
wavelength domain where the permanent dipole is most efficient. This effect is
used to induce an appreciable isotope separation.Comment: Physical Review Letters, 1995 (in press). 4 pages in revtex format, 3
uuencoded figures. Full postcript version available at:
http://chemphys.weizmann.ac.il/~charron/prl.ps or
ftp://scipion.ppm.u-psud.fr/coherent.control/prl.p
Quantum key distribution and 1 Gbit/s data encryption over a single fibre
We perform quantum key distribution (QKD) in the presence of 4 classical
channels in a C-band dense wavelength division multiplexing (DWDM)
configuration using a commercial QKD system. The classical channels are used
for key distillation and 1 Gbps encrypted communication, rendering the entire
system independent from any other communication channel than a single dedicated
fibre. We successfully distil secret keys over fibre spans of up to 50 km. The
separation between quantum channel and nearest classical channel is only 200
GHz, while the classical channels are all separated by 100 GHz. In addition to
that we discuss possible improvements and alternative configurations, for
instance whether it is advantageous to choose the quantum channel at 1310 nm or
to opt for a pure C-band configuration.Comment: 9 pages, 7 figure
A quantitative theory-versus-experiment comparison for the intense laser dissociation of H2+
A detailed theory-versus-experiment comparison is worked out for H
intense laser dissociation, based on angularly resolved photodissociation
spectra recently recorded in H.Figger's group. As opposite to other
experimental setups, it is an electric discharge (and not an optical
excitation) that prepares the molecular ion, with the advantage for the
theoretical approach, to neglect without lost of accuracy, the otherwise
important ionization-dissociation competition. Abel transformation relates the
dissociation probability starting from a single ro-vibrational state, to the
probability of observing a hydrogen atom at a given pixel of the detector
plate. Some statistics on initial ro-vibrational distributions, together with a
spatial averaging over laser focus area, lead to photofragments kinetic
spectra, with well separated peaks attributed to single vibrational levels. An
excellent theory-versus-experiment agreement is reached not only for the
kinetic spectra, but also for the angular distributions of fragments
originating from two different vibrational levels resulting into more or less
alignment. Some characteristic features can be interpreted in terms of basic
mechanisms such as bond softening or vibrational trapping.Comment: submitted to PRA on 21.05.200
Feasibility of quantum key distribution through dense wavelength division multiplexing network
In this paper, we study the feasibility of conducting quantum key
distribution (QKD) together with classical communication through the same
optical fiber by employing dense-wavelength-division-multiplexing (DWDM)
technology at telecom wavelength. The impact of the classical channels to the
quantum channel has been investigated for both QKD based on single photon
detection and QKD based on homodyne detection. Our studies show that the latter
can tolerate a much higher level of contamination from the classical channels
than the former. This is because the local oscillator used in the homodyne
detector acts as a "mode selector" which can suppress noise photons
effectively. We have performed simulations based on both the decoy BB84 QKD
protocol and the Gaussian modulated coherent state (GMCS) QKD protocol. While
the former cannot tolerate even one classical channel (with a power of 0dBm),
the latter can be multiplexed with 38 classical channels (0dBm power each
channel) and still has a secure distance around 10km. Preliminary experiment
has been conducted based on a 100MHz bandwidth homodyne detector.Comment: 18 pages, 5 figure
Ponderomotive effects in zero kinetic energy photoelectron spectroscopy with intense femtosecond pulses
Zero kinetic energy photoelectron (ZEKE) spectroscopy may be an interesting technique for monitoring the time evolution of state selected atomic products in ultrafast pump-probe experiments. We investigate here the effects of laser intensity by studying three-photon non-resonant ZEKE spectra of atomic xenon at the first ionization threshold with tunable femtosecond UV pulses. High intensity introduces a new broadening due to ponderomotive effects in the ZEKE spectrum. It is demonstrated that a three-photon ZEKE spectrum can be recorded at intensities where the broadenign due to these ponderomotive effects (i.e. the ac Stark shift for high-n Rydberg states) is small in comparison with the effective laser bandwidth.NRC publication: Ye
Space charge and plasma effects in zero kinetic energy (ZEKE)photoelectron spectroscopy
In photoelectron spectroscopy experiments it is generally assumed that the Coulomb force between charged particles is small compared with external fields, and that the free kinetic electrons will quickly leave the ions. This is the basis of the ZEKE photoelectron spectroscopy. However as the density of charged particles is increased, plasma physics effects begin to become important, and the kinetic electrons become trapped by the net positive charge and move so as to set up a self-field which can cancel any externally imposed electric fields. For high densities, fewer electrons than expected are able to escape the self-field. The production of self-consistent electric fields is studied by means of particle-in-cell plasma simulations and by N-body trajectory calculations, and simple expressions are derived for when plasma physics effects become significant. An experimental illustration of plasma effects in ZEKE is presented.Peer reviewed: YesNRC publication: Ye
Direct autocorrelation measurements of mid-infrared picosecond pulses by quantum-well devices
We report the direct autocorrelation of ultrashort mid-infrared laser pulses, using an unbiased GaAsy/GaAlAs quantum-well device as a nonlinear photovoltaic medium. Using this method, we autocorrelate ultrashort (3-ps) low-energy (~500-nJ) pulses of 10.6-\ub5m light. This approach should permit the autocorrelation of subpicosecond infrared pulses.Peer reviewed: YesNRC publication: Ye