Search results for "Picosecond"

Backward second-harmonic generation of near infrared picosecond pulses

2014

We report on backward second-harmonic generation using picosecond laser pulses in congruent lithium niobate with 3.2 µm periodic poling. By tuning both the pump wavelength and the sample temperature, we observed three resonant peaks in the range 1530-1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders, respectively. A maximum conversion efficiency of 0.475% was achieved at the 16th order with a 10 kW peak pump power. The latter is the highest conversion reported in bulk to date, for the backward configuration, with an improvement greater than 50% with respect to those previously achieved with nanosecond pulses for the same order of resonance.

Ultrafast Photo-Dynamics of a Reversible Photochromic Spiropyran

2002

We report the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1‘,3‘,3‘-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (6,8-dinitro BIPS) and its 1‘-(2-carboxyethyl) substituted derivative. The reaction is fast and essentially over in a few hundred picoseconds. The rate of MC-S1 state decay evaluated from transient absorbance can be correlated directly with the MC-S1 state lifetime as determined using stimulated and ordinary emission measurements. The recovery of the MC-S0 state from MC-S1 has a component with a lifetime of 60−78 ps in acetonitrile with a second component of 350−470 ps probably due to a metastable intermediate. We …

Efficient energy conversion for cubic third-harmonic generation that is phase matched in KTiOPO(4).

2000

We demonstrate, for the first time to our knowledge, that efficient third-harmonic generation can be achieved with a cubic contribution much larger than the quadratic processes. An energy-conversion efficiency of 2.4% is achieved for cubic third-harmonic generation that is phase matched along the x axis of a KTiOPO(4) crystal by use of a picosecond fundamental laser emitting at 1618 nm. The associated cascading processes are only 10% of the pure cubic interaction, which is very suitable for study of the specific quantum optical correlations. Calculations of the third-harmonic generation conversion efficiency with respect to group-velocity dispersion and to the longitudinal Gaussian beam pro…

Ultrafast excitation dynamics of low energy pigments in reconstituted peripheral light-harvesting complexes of photosystem I

2000

AbstractUltrafast dynamics of a reconstituted Lhca4 subunit from the peripheral LHCI-730 antenna of photosystem I of higher plants were probed by femtosecond absorption spectroscopy at 77 K. Intramonomeric energy transfer from chlorophyll (Chl) b to Chl a and energy equilibration between Chl a molecules observed on the subpicosecond time scale are largely similar to subpicosecond energy equilibration processes within LHCII monomers. However, a 5 ps equilibration process in Lhca4 involves unique low energy Chls in LHCI absorbing at 705 nm. These pigments localize the excitation both in the Lhca4 subunit and in LHCI-730 heterodimers. An additional 30–50 ps equilibration process involving red …

Picosecond absorption spectroscopy: Methods and applications in photophysical and photochemical systems

1985

Remitted photon path length in human skin, skin phantoms and cell cultures

2020

An experimental method for remitted photon path length measurements in scattering media has been developed and tested on human skin and skin neoplasms, skin phantoms and cell cultures. The photon time-of-flight (PTOF) measurement method was used in this study, where the photon travel time was converted into path length. Remitted light signals were obtained using a picosecond broadband laser and a set of narrowband interference filters in spectral rang 520 – 760 nm. Five different distances of 1, 8, 12, 16 and 20 mm between the source and detector fibers were used. Measurements were performed at different wavelengths and distance combinations; they were taken from human skin and skin malform…

Ultrafast stimulated Raman parallel adiabatic passage by shaped pulses

2009

We present a general and versatile technique of population transfer based on {\it parallel adiabatic passage} by femtosecond shaped pulses. Their amplitude and phase are specifically designed to optimize the adiabatic passage corresponding to parallel eigenvalues at all times. We show that this technique allows the robust adiabatic population transfer in a Raman system with the total pulse area as low as 3 $\pi$, corresponding to a fluence of one order of magnitude below the conventional stimulated Raman adiabatic passage process. This process of short duration, typically pico- and subpicosecond, is easily implementable with the modern pulse shaper technology and opens the possibility of ul…

Si and Si-rich silicon-nitride waveguides for optical transmissions and nonlinear applications around 2 µm

2019

We show that cm-long silicon and silicon-rich silicon nitride waveguides with subwavelength transverse dimensions can efficiently sustain high-speed transmissions at 2 μm. We report the transmission of a 10 Gbit/s signal with negligible power penalty. Parametric conversion in both continuous and pulsed pump regimes is also demonstrated, as well as the spectral broadening of picosecond pulses.

Generation of aperiodic picosecond pulses sequences from incoherent optical waves

2007

We present an original method to generate optical pulses trains with random time-interval values from incoherent broadband sources. Our technique relies on the remarkable properties of a line made of cascaded SPM-based optical regenerators.

All-fibered high-quality 28-GHz to 112 GHz pulse sources based on nonlinear compression of optical temporal besselons

2021

The generation of high quality pulse trains at repetition rates of several tens of GHz remains a crucial step for optical telecommunications, optical sampling or component testing applications. Unfortunately, the current bandwidth limitations of optoelectronic devices do not allow the direct generation of well-defined optical pulse trains with low duty cycles. An attractive solution is based on a direct temporal phase modulation that is then converted into an intensity modulation thanks to a dispersive element that imprints a spectral quadratic phase. Picosecond pulses at repetition rates of several tens of GHz have been successfully demonstrated [1] . However, this approach suffers from a …