Naphthalocyanine-based time reversal mirror at 800 nm

International audienceWe performed pulse shaping and time reversal experiments using spectral holography based on persistent spectral hole burning in free-base naphthalocyanine-doped films. The application of a new pulse re-compression scheme based on a programmable hole burning material acting as a time reversal mirror is considered. In this work, we adapted the Fourier transform spectral interferometry technique for measuring the amplitude and phase of photon echo signals produced by diffraction of femtosecond pulses on a spectral hologram. We therefore demonstrated that we could control the pulses diffracted from the hologram by shaping and then characterizing these pulses in both amplitude and phase by spectral interferometry. © 2003 Elsevier B.V. All rights reserved

Amplitude and phase measurements of femtosecond pulses shaped using spectral hole burning in free-base naphthalocyanine-doped films.

In this work we use a technique of spectroscopy adapted for measuring the amplitude and phase of photon echo signals [7] produced by diffraction of a fs pulse on a spectral hologram. We also improved the technique in terms of spectral resolution in order to measure photon echoes delayed by a few tens of picoseconds. Our study is focused on measuring the coherence time of the sample using a photon echo experiment in the photochemically accumulated regime and on demonstrating the pulse-shaping and time-reversal potentialities of our photo-sensitive material. Spectral holograms are formed through persistent spectral hole burning using a sequence of 2 pump pulses separated by a time delay, in a collinear geometry. The sample is a free base naphtalocyanine embedded in polyvinylbutyral (H2NPc/PVB). The absorption peaks at 783 nm and is 20 nm large (FWHM). Our laser source is a 15-fs, 100MHz, Ti:S oscillator

Amplitude and phase measurements of femtosecond pulses shaped using spectral hole burning in free-base naphthalocyanine-doped films.

In this work we use a technique of spectroscopy adapted for measuring the amplitude and phase of photon echo signals [7] produced by diffraction of a fs pulse on a spectral hologram. We also improved the technique in terms of spectral resolution in order to measure photon echoes delayed by a few tens of picoseconds. Our study is focused on measuring the coherence time of the sample using a photon echo experiment in the photochemically accumulated regime and on demonstrating the pulse-shaping and time-reversal potentialities of our photo-sensitive material. Spectral holograms are formed through persistent spectral hole burning using a sequence of 2 pump pulses separated by a time delay, in a collinear geometry. The sample is a free base naphtalocyanine embedded in polyvinylbutyral (H2NPc/PVB). The absorption peaks at 783 nm and is 20 nm large (FWHM). Our laser source is a 15-fs, 100MHz, Ti:S oscillator

Amplitude and phase measurements of femtosecond pulses shaped by use of spectral hole burning in free-base naphthalocyanine-doped films

no abstrac

Amplitude and phase measurements of femtosecond pulses shaped using spectral hole burning in free-base naphthalocyanine-doped films.

In this work we use a technique of spectroscopy adapted for measuring the amplitude and phase of photon echo signals [7] produced by diffraction of a fs pulse on a spectral hologram. We also improved the technique in terms of spectral resolution in order to measure photon echoes delayed by a few tens of picoseconds. Our study is focused on measuring the coherence time of the sample using a photon echo experiment in the photochemically accumulated regime and on demonstrating the pulse-shaping and time-reversal potentialities of our photo-sensitive material. Spectral holograms are formed through persistent spectral hole burning using a sequence of 2 pump pulses separated by a time delay, in a collinear geometry. The sample is a free base naphtalocyanine embedded in polyvinylbutyral (H2NPc/PVB). The absorption peaks at 783 nm and is 20 nm large (FWHM). Our laser source is a 15-fs, 100MHz, Ti:S oscillator

Femtosecond pulse shaping based on spectral hole burning

International audienc

Amplitude and phase measurements of femtosecond pulses shaped by use of spectral hole burning in free-base naphthalocyanine-doped films

no abstrac

Amplitude and phase measurements of femtosecond pulses shaped using spectral hole burning in free-base naphthalocyanine-doped films.

International audienceIn this work we use a technique of spectroscopy adapted for measuring the amplitude and phase of photon echo signals [7] produced by diffraction of a fs pulse on a spectral hologram. We also improved the technique in terms of spectral resolution in order to measure photon echoes delayed by a few tens of picoseconds. Our study is focused on measuring the coherence time of the sample using a photon echo experiment in the photochemically accumulated regime and on demonstrating the pulse-shaping and time-reversal potentialities of our photo-sensitive material. Spectral holograms are formed through persistent spectral hole burning using a sequence of 2 pump pulses separated by a time delay, in a collinear geometry. The sample is a free base naphtalocyanine embedded in polyvinylbutyral (H2NPc/PVB). The absorption peaks at 783 nm and is 20 nm large (FWHM). Our laser source is a 15-fs, 100MHz, Ti:S oscillator

The influence of carbon dioxide on brain activity and metabolism in conscious humans

A better understanding of carbon dioxide (CO2) effect on brain activity may have a profound impact on clinical studies using CO2 manipulation to assess cerebrovascular reserve and on the use of hypercapnia as a means to calibrate functional magnetic resonance imaging (fMRI) signal. This study investigates how an increase in blood CO2, via inhalation of 5% CO2, may alter brain activity in humans. Dynamic measurement of brain metabolism revealed that mild hypercapnia resulted in a suppression of cerebral metabolic rate of oxygen (CMRO2) by 13.4%±2.3% (N=14) and, furthermore, the CMRO2 change was proportional to the subject's end-tidal CO2 (Et-CO2) change. When using functional connectivity MRI (fcMRI) to assess the changes in resting-state neural activity, it was found that hypercapnia resulted in a reduction in all fcMRI indices assessed including cluster volume, cross-correlation coefficient, and amplitude of the fcMRI signal in the default-mode network (DMN). The extent of the reduction was more pronounced than similar indices obtained in visual-evoked fMRI, suggesting a selective suppression effect on resting-state neural activity. Scalp electroencephalogram (EEG) studies comparing hypercapnia with normocapnia conditions showed a relative increase in low frequency power in the EEG spectra, suggesting that the brain is entering a low arousal state on CO2 inhalation