288 research outputs found
Transient coherent Raman scattering in the time and frequency domain
A new type of Raman spectroscopy is presented: After transient excitation of molecular modes coherently scattered Raman spectra are investigated in a depayed probing experiment. The spectral position of the Raman mode is observed after long delay times. The dephasing time is obtained from the time dependence of the scattered amplitudes. Frequency disturbing non-resonant susceptibilities are eliminated. We report on first experimental results of transient coherent Raman spectroscopy of liquid CH3CCl3
Relaxed damage threshold intensity conditions and nonlinear increase in the conversion efficiency of an optical parametric oscillator using a bi-directional pump geometry
A novel bi-directional pump geometry that nonlinearly increases the nonlinear optical conversion efficiency of a synchronously pumped optical parametric oscillator (OPO) is reported. This bi-directional pumping method synchronizes the circulating signal pulse with two counter-propagating pump pulses within a linear OPO resonator. Through this pump scheme, an increase in nonlinear optical conversion efficiency of 22% was achieved at the signal wavelength, corresponding to a 95% overall increase in average power. Given an almost unchanged measured pulse duration of 260 fs under optimal performance conditions, this related to a signal wavelength peak power output of 18.8 kW, compared with 10 kW using the traditional single-pass geometry. In this study, a total effective peak intensity pump-field of 7.11 GW/cm(2) (corresponding to 3.55 GW/cm(2) from each pump beam) was applied to a 3 mm long periodically poled lithium niobate crystal, which had a damage threshold intensity of 4 GW/cm(2), without impairing crystal integrity. We therefore prove the application of this novel pump geometry provides opportunities for power-scaling of synchronously pumped OPO systems together with enhanced nonlinear conversion efficiency through relaxed damage threshold intensity conditions
Narrowing of spectral lines beyond the natural or dephasing line width
Transient excitation and gated or delayed observation provides a narrowing of the inherent line width of the transition. Possible experimental one- and two-photon systems are discussed and the loss of signal with line narrowing is calculated. The general case of lines broadened by dephasing processes is treated. Contact is made with the line narrowing in recent Raman type experiments
Second harmonic beam analysis, a sensitive technique to determine the duration of single ultrashort laser pulses
The second harmonic beam generated in a noncollinear arrangement allows the observation of the autocorrelation functio: A compact optical beam splitter and imaging system eliminates alignment problems. Single pulses of 1 ps duration and approximately 10−8 joule energy are readily observed using an optical multichannel analyser
Waveguide-based OPO source of entangled photon pairs
In this paper we present a compact source of narrow-band energy-time
entangled photon pairs in the telecom regime based on a Ti-indiffused
Periodically Poled Lithium Niobate (PPLN) waveguide resonator, i.e. a waveguide
with end-face dielectric multi-layer mirrors. This is a monolithic doubly
resonant Optical Parametric Oscillator (OPO) far below threshold, which
generates photon pairs by Spontaneous Parametric Down Conversion (SPDC) at
around 1560nm with a 117MHz (0.91 pm)- bandwidth. A coherence time of 2.7 ns is
estimated by a time correlation measurement and a high quality of the entangled
states is confirmed by a Bell-type experiment. Since highly coherent
energy-time entangled photon pairs in the telecom regime are suitable for long
distance transmission and manipulation, this source is well suited to the
requirements of quantum communication.Comment: 13 page
Time resolved observation of resonant and non-resonant contributions to the nonlinear susceptibility χ(3)
The resonant and nonresonant part of χ(3) are distinguished by their different time behavior. The medium is coherently excited by two picosecond light pulses of defined frequency difference and the state of the system is monitored by a third properly delayed probe pulse. Results are presented on neat liquids of carbontetrachloride and cyclohexane and on the mixture of CCl4: C6H12
Engineering integrated pure narrow-band photon sources
Engineering and controlling well defined states of light for quantum
information applications is of increasing importance as the complexity of
quantum systems grows. For example, in quantum networks high multi-photon
interference visibility requires properly devised single mode sources. In this
paper we propose a spontaneous parametric down conversion source based on an
integrated cavity-waveguide, where single narrow-band, possibly distinct,
spectral modes for the idler and the signal fields can be generated. This mode
selection takes advantage of the clustering effect, due to the intrinsic
dispersion of the nonlinear material. In combination with a CW laser and fast
detection, our approach provides a means to engineer a source that can
efficiently generate pure photons, without filtering, that is compatible with
long distance quantum communication. Furthermore, it is extremely flexible and
could easily be adapted to a wide variety of wavelengths and applications.Comment: 13 pages, 7 figure
Counter-propagating entangled photons from a waveguide with periodic nonlinearity
The conditions required for spontaneous parametric down-conversion in a
waveguide with periodic nonlinearity in the presence of an unguided pump field
are established. Control of the periodic nonlinearity and the physical
properties of the waveguide permits the quasi-phase matching equations that
describe counter-propagating guided signal and idler beams to be satisfied. We
compare the tuning curves and spectral properties of such counter-propagating
beams to those for co-propagating beams under typical experimental conditions.
We find that the counter-propagating beams exhibit narrow bandwidth permitting
the generation of quantum states that possess discrete-frequency entanglement.
Such states may be useful for experiments in quantum optics and technologies
that benefit from frequency entanglement.Comment: submitted to Phys. Rev.
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