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ABSTRACT: Autoionization in argon atoms was studied by transient absorption spectroscopy with isolated attosecond XUV pulses. The peak position, line shape and population of the resonant states were modified by intense near infrared laser pulses.
Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
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11/2010; , ISBN: 978-953-307-242-5
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ABSTRACT: Autoionization of argon atoms was studied experimentally by transient absorption spectroscopy with isolated attosecond pulses. The peak position, intensity, linewidth, and shape of the 3s3p⁶np ¹P Fano resonance series (26.6-29.2 eV) were modified by intense few-cycle near infrared laser pulses, while the delay between the attosecond pulse and the laser pulse was changed by a few femtoseconds. Numerical simulations revealed that the experimentally observed splitting of the 3s3p⁶4p ¹P line is caused by the coupling between two short-lived highly excited states in the strong laser field.
Physical Review Letters 10/2010; 105(14):143002. · 7.37 Impact Factor
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ABSTRACT: The time delay between the pump and probe pulses in attosecond time-resolved experiments, such as attosecond streaking, is commonly introduced by splitting and recombining the two pulses in an interferometer. This technique suffers from instability in the optical path lengths of the two arms due to mechanical vibration of the optical elements and fluctuating environmental conditions. We present a technique with which the instability of the unconventional interferometer is suppressed while at the same time the time delay is controlled to within 20 as RMS using a feedback loop. Using this scheme, the streaked spectrogram of an attosecond pulse was measured.
Optics Express 11/2009; 17(24):21459-64. · 3.59 Impact Factor
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ABSTRACT: Double optical gating of high-harmonic generation was used to obtain supercontinuous spectra in the extreme UV (XUV) region including the water window. The spectra supported a 16 as pulse duration that is below one atomic unit of time (24 as). The dependence of the gated spectra on the carrier-envelope phase of the laser provided evidence that isolated attosecond pulses were generated. In addition, to ensure the temporal coherence of the XUV light, the pulse shape and phase of isolated 107 as XUV pulses using a portion of the spectrum were characterized by attosecond streaking.
Optics Letters 11/2009; 34(21):3337-9. · 3.40 Impact Factor
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ABSTRACT: Carrier-envelope (CE) phase stabilization of a two-stage chirped pulse amplifier laser system with regenerative amplification as the preamplifier is demonstrated. The CE phase stability of this laser system is found to have a 90 mrad rms error averaged over 50 laser shots for a locking period of 4.5 h. The CE phase locking was confirmed unambiguously by experimental observation of the 2pi periodicity of the high-order harmonic spectrum generated by double optical gating.
Applied Optics 10/2009; 48(30):5692-5. · 1.41 Impact Factor
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ABSTRACT: We report a double feedback loop for the improvement of the carrier-envelope phase stabilization of a chirped mirror based femtosecond laser oscillator. By combining the control of the Ti:sapphire crystal temperature and the modulation of the pump power, the carrier envelope offset frequency, fCEO, was locked for close to 20 h, which is much longer than the typical phase stabilization time with only pump power modulation.
Applied Optics 09/2009; 48(27):5127-30. · 1.41 Impact Factor
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ABSTRACT: The attosecond streaking technique is used for the characterization of isolated extreme ultraviolet (XUV) attosecond pulses. This type of measurement suffers from low photoelectron counts in the streaked spectrogram, and is thus susceptible to shot noise. For the retrieval of few- or mono-cycle attosecond pulses, high-intensity streaking laser fields are required, which cause the energy spectrum of above-threshold ionized (ATI) electrons to overlap with that of the streaked photoelectrons. It is found by using the principal component generalized projections algorithm that the XUV attosecond pulse can accurately be retrieved for simulated and experimental spectrograms with a peak value of 50 or more photoelectron counts. Also, the minimum streaking intensity is found to be more than 50 times smaller than that required by the classical streaking camera for retrieval of pulses with a spectral bandwidth supporting 90 as transform-limited pulse durations. Furthermore, spatial variation of the streaking laser intensity, collection angle of streaked electrons and time delay jitter between the XUV pulse and streaking field can degrade the quality of the streaked spectrogram. We find that even when the XUV and streaking laser focal spots are comparable in size, the streaking electrons are collected from a 4π solid angle, or the delay fluctuates by more than the attosecond pulse duration, the attosecond pulses can still be accurately retrieved. In order to explain the insusceptibility of the streaked spectrogram to these factors, the linearity of the streaked spectrogram with respect to the streaking field is derived under the saddle point approximation.
Journal of Physics B Atomic Molecular and Optical Physics 06/2009; 42(13):134007. · 1.88 Impact Factor
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ABSTRACT: When isolated attosecond pulses are reconstructed from an ideal streaked photoelectron spectrogram, the relative amplitude of accompanying satellite pulses can be identified from their interference. However, the interference pattern in the spectrogram can be smeared by variation of the streaking laser intensity in the focal volume and by interpolation when using large delay steps acquiring the spectrogram, making accurate measurement of the relative intensity of the satellite pulses difficult. We investigate these effects on the reconstruction of satellite pulses with full- and half-cycle separations. Our simulations show that satellite pulses with full-cycle separation are largely unaffected by these issues.
Applied Physics Letters 04/2009; 94(16):161112-161112-3. · 3.84 Impact Factor
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ABSTRACT: Carrier-envelope phase stabilization of a two-stage chirped pulse amplifier laser system with regenerative amplification as the preamplifier is demonstrated with a 90 mrad rms error for a locking period of 4.5 h. 2010 Conference on Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS), San Jose, California, May 16-21, 2010
