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1.
Rev Sci Instrum ; 85(6): 064904, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24985839

RESUMO

GigaHertz (GHz) thermoreflectance technique is developed to measure the transient temperature of metal and semiconductor materials located behind an opaque surface. The principle is based on the synchronous detection, using a commercial THz pyrometer, of a modulated millimeter wave (at 110 GHz) reflected by the sample hidden behind a shield layer. Measurements were performed on aluminum, copper, and silicon bulks hidden by a 5 cm thick Teflon plate. We report the first measurement of the thermoreflectance coefficient which exhibits a value 100 times higher at 2.8 mm radiation than those measured at visible wavelengths for both metallic and semiconductor materials. This giant thermoreflectance coefficient κ, close to 10(-3) K(-1) versus 10(-5) K(-1) for the visible domain, is very promising for future thermoreflectance applications.

2.
Opt Express ; 19(6): 5105-17, 2011 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-21445145

RESUMO

3D terahertz computed tomography has been performed using a monochromatic millimeter wave imaging system coupled with an infrared temperature sensor. Three different reconstruction methods (standard back-projection algorithm and two iterative analysis) have been compared in order to reconstruct large size 3D objects. The quality (intensity, contrast and geometric preservation) of reconstructed cross-sectional images has been discussed together with the optimization of the number of projections. Final demonstration to real-life 3D objects has been processed to illustrate the potential of the reconstruction methods for applied terahertz tomography.

3.
Phys Rev Lett ; 103(2): 028104, 2009 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-19659250

RESUMO

Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray sources offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-harmonic x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.


Assuntos
Difração de Raios X/métodos , Processamento de Imagem Assistida por Computador/métodos , Lasers
4.
Phys Rev Lett ; 100(14): 143902, 2008 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-18518033

RESUMO

We have investigated the intensity dependence of high-order harmonic generation in argon when the two shortest quantum paths contribute to the harmonic emission. For the first time to our knowledge, experimental conditions were found to clearly observe interference between these two quantum paths that are in excellent agreement with theoretical predictions. This result is a first step towards the direct experimental characterization of the full single-atom dipole moment and demonstrates an unprecedented accuracy of quantum path control on an attosecond time scale.

5.
Opt Lett ; 32(11): 1498-500, 2007 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-17546167

RESUMO

We report what is to our knowledge the first demonstration of spatial filtering of a high-order harmonic beam into a soft-x-ray laser plasma amplifier at 32.8 nm. After amplification the seed energy is enhanced by a factor of 50, and the beam profile of the amplified beam exhibits an Airy-like shape due to the spatial filtering by the optical field ionized plasma. Moreover, the transverse coherence of the spatially filtered amplified beam is strongly enhanced, resulting in the generation of a peak coherent power of 0.9 x 10(5) to 1.8 x 10(5) W.

6.
Phys Rev Lett ; 95(15): 153902, 2005 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-16241726

RESUMO

We experimentally investigate the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned CO2 molecules. The recombination interference effect is clearly seen through the order dependence of the harmonic yield in an aligned sample. The experimental results can be well modeled assuming that the effective de Broglie wavelength of the returning electron wave is not significantly altered by the Coulomb field of the molecular ion. We demonstrate that such interference effects can be effectively controlled by changing the ellipticity of the driving laser field.

7.
Phys Rev Lett ; 94(19): 193903, 2005 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-16090174

RESUMO

By using a self-referencing technique, we have experimentally measured the influence of the carrier-envelope phase of femtosecond light pulses on the phase of the electric field of the radiation produced by high-order harmonic generation. We show that, in particular experimental conditions, the temporal evolution of the electric field of the attosecond pulses, is directly controlled by the carrier-envelope phase of the driving pulses.

8.
Phys Rev Lett ; 89(4): 047401, 2002 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-12144498

RESUMO

A model is proposed to account for Kerr-like nonlinearity induced by femtosecond pulses via terahertz generation and electro-optical effect. This phenomenon, so far overlooked, is evidenced in a zinc blende single crystal with a heterodyne optical Kerr effect setup. The spectral evolution of this phenomenon as well as its noninstantaneous response character are reported. Its competition with a third-order optical Kerr effect is demonstrated.

9.
Opt Express ; 9(4): 172-7, 2001 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-19421286

RESUMO

The second harmonic generation in a thin ss-barium borate crystal is used to measure chi ((2)) cascading phenomena in the spectral domain. The harmonic generation is induced by two pulses produced by spectrally filtering a femtosecond pulse and centered at the wavelength lambda -Delta lambda and lambda +Delta lambda. New spectral components appear in spectral density of both the fundamental and harmonic pulses. High order cascading phenomena are evidenced. In good agreement with theoretical predictions, for large phase mismatch the evolution of the spectra demonstrates the competition between cascaded chi(2) and chi(3) phenomena.

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