255 research outputs found
Femtosecond spectral electric field reconstruction using coherent transients
We have implemented a new approach for measuring the time-dependent intensity
and phase of ultrashort optical pulses. It is based on the interaction between
shaped pulses and atoms, leading to coherent transients.Comment: 4 pages Accepted in Optics Letter
Space-time coupling of shaped ultrafast ultraviolet pulses from an acousto-optic programmable dispersive filter
A comprehensive experimental analysis of spatio-temporal coupling effects
inherent to the acousto-optic programmable dispersive filter (AOPDF) is
presented. Phase and amplitude measurements of the AOPDF transfer function are
performed using spatially and spectrally resolved interferometry.
Spatio-temporal and spatio-spectral coupling effects are presented for a range
of shaped pulses that are commonly used in quantum control experiments. These
effects are shown to be attributable to a single mechanism: a
group-delay--dependent displacement of the shaped pulse. The physical mechanism
is explained and excellent quantitative agreement between the measured and
calculated coupling speed is obtained. The implications for quantum control
experiments are discussed.Comment: 8 pages, 6 figures; accepted for publication within JOSA
Real time Quantum state holography using coherent transients
In a two level atom, real-time quantum state holography is performed through
interferences between quantum states created by a reference pulse and a chirped
pulse resulting in coherent transients. A sequence of several measurements
allows one to measure the real and imaginary parts of the excited state wave
function. These measurements are performed during the interaction with the
ultrashort laser pulse. The extreme sensitivity of this method to the pulse
shape provides a tool for electric field measurement
Ultrashort pulse characterization by spectral shearing interferometry with spatially chirped ancillae
We report a new version of spectral phase interferometry for direct electric
field reconstruction (SPIDER), which enables consistency checking through the
simultaneous acquisition of multiple shears and offers a simple and precise
calibration method. By mixing the test pulse with two spatially chirped ancilla
fields we generate a single-shot interferogram which contains multiple shears,
the spectral amplitude of the test pulse, and the reference phase, which is
accurate for broadband pulses. All calibration parameters - shear,
upconversion-frequency and reference phase position - can be accurately
obtained from a single calibration trace.Comment: 11 pages, 7 figure
Mesoscopic self-collimation and slow light in all-positive index layered photonic crystals
We demonstrate a mesoscopic self-collimation effect in photonic crystal
superlattices consisting of a periodic set of all-positive index 2D photonic
crystal and homogeneous layers. We develop an electromagnetic theory showing
that diffraction-free beams are observed when the curvature of the optical
dispersion relation is properly compensated for. This approach allows to
combine slow light regime together with self-collimation in photonic crystal
superlattices presenting an extremely low filling ratio in air.Comment: 4 pages, 4 figure
Time-dependent photoionization of azulene: Optically induced anisotropy on the femtosecond scale
We measure the photoionization cross-section of vibrationally excited levels
in the S2 state of azulene by femtosecond pump-probe spectroscopy. At the
wavelengths studied (349-265 nm in the pump) the transient signals exhibit two
distinct and well-defined behaviours: (i) Short-term (on the order of a
picosecond) polarization dependent transients and (ii) longer (10 ps - 1 ns)
time-scale decays. This letter focuses on the short time transient. In contrast
to an earlier study by Diau et al.22 [J. Chem. Phys. 110 (1999) 9785.] we
unambiguously assign the fast initial decay signal to rotational dephasing of
the initial alignment created by the pump transition.Comment: Chemical Physics Letters (2008
Shaping speckles: spatio-temporal focussing of an ultrafast pulse through a multiply scattering medium
The multiple scattering of coherent light is a problem of both fundamental
and applied importance. In optics, phase conjugation allows spatial focussing
and imaging through a multiply scattering medium; however, temporal control is
nonetheless elusive, and multiple scattering remains a challenge for
femtosecond science. Here, we report on the spatially and temporally resolved
measurement of a speckle field produced by the propagation of an ultrafast
optical pulse through a thick strongly scattering medium. Using spectral pulse
shaping, we demonstrate the spatially localized temporal recompression of the
output speckle to the Fourier-limit duration, offering an optical analogue to
time-reversal experiments in the acoustic regime. This approach shows that a
multiply scattering medium can be put to profit for light manipulation at the
femtosecond scale, and has a diverse range of potential applications that
includes quantum control, biological imaging and photonics.Comment: 7 pages, 3 figures, published in Nature Communication
High frequency operation of an integrated electro-absorption modulator onto a vertical-cavity surface-emitting laser
We present in this paper the vertical integration of an electro-absorption modulator (EAM) onto a vertical-cavity surface-emitting laser (VCSEL). We discuss the design, fabrication, and measured characteristics of the combined VCSEL and EAM. We previously demonstrated a standalone EAM with an optical bandwidth around 30 GHz. In this paper we present for the first time an optical bandwidth of 30 GHz for an EAM integrated onto a VCSEL. This device exhibits single-mode operation and a very low chirp, below 0.1 nm, even with a modulation depth of 70% which makes this device very competitive for high-speed communications in data centers
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