The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10-15 s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope ...and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 × 10-18 s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents-these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We generated a series of harmonics in a xenon gas jet inside a cavity seeded by pulses from a Ti:sapphire mode-locked laser with a repetition rate of 10.8 MHz. Harmonics up to 19th order at 43 nm ...were observed with plateau harmonics at the microW power level. An elaborate dispersion compensation scheme and the use of a moderate repetition rate allowed for this significant improvement in output power of the plateau harmonics of 4 orders of magnitude over previous results. With this power level and repetition rate, high-resolution spectroscopy in the extreme ultraviolet region becomes conceivable. An interesting target would be the 1S-2S transition in hydrogenlike He+ at 60 nm.
We demonstrate phase stable, mJ-level parametric amplification of pulse pairs originating from a Ti:Sapphire frequency comb laser. The amplifier-induced phase shift between the pulses has been ...determined interferometrically with an accuracy of approximately 10 mrad. Typical phase shifts are on the order of 50-200 mrad, depending on the operating conditions. The measured phase-relation can be as stable as 20 mrad rms (1/300(th) of an optical cycle). This makes the system suitable for Ramsey spectroscopy at short wavelengths by employing harmonic upconversion of the double-pulses in nonlinear media.
We report measurements of the response of a Kerr-lens mode-locked Ti:sapphire frequency comb to pump power modulation. For each setting of the laser, the comb expands and contracts about a particular ...fixed point in frequency. We measured this fixed point and found that it is within 8% of our frequency comb's center. In addition, we found that as we shift the comb's center frequency, the fixed point follows to some extent. It follows that modulating the pump power mostly affects the comb's group velocity, i.e., the repetition rate.
Frequency comb generation and excitation of argon, neon, and helium is shown from 51 to 85 nm with amplified and harmonically upconverted comb laser pulses, resulting in an 8-fold improved helium ...ground state ionization energy.
Femtosecond metrology Holzwarth, T.U.R.; Zimmermann, M.; Gohle, C. ...
2003 Digest of LEOS Summer Topical Meeting (Cat. No.03TH8701),
2003
Conference Proceeding
Possibilities of frequency combs generated by femtosecond lasers in high precision spectroscopy on atomic hydrogen was explored at the 10/sup -14/ level. Fundamental tests of the fs frequency comb ...technique were done. Further applications arise in the time domain where the phase between the carrier and the envelope of a pulse can now be determined, allowing the production of isolated XUV attosecond pulses.
Intracavity high harmonic generation is demonstrated in an external cavity, seeded by a Ti:sapphire mode-locked laser at a repetition rate of 10.8MHz. Harmonics up to 19th order at 43 nm were ...observed with plateau harmonics at the μW power level.
The capability of frequency-comb (FC) lasers to precisely measure optical frequencies has been extended to the to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), corresponding to ...frequencies of multiple PHz. We demonstrate "broad frequency comb generation" for a wavelength range of 51-85 nm. Our method is based on amplification and coherent up-conversion of a pair of pulses originating from a near-infrared femtosecond FC laser. Excitation of argon, neon, and helium with these upconverted laser pulses in the XUV lead to Ramsey-like signals with up to 61% contrast. From these signals an accuracy of 6 MHz has been achieved in the determination of the ground state ionization energy of helium at 51 nm. Further improvement to a kHz-level accuracy is expected based on a new pump laser for the employed parametric amplification system.
Widely tunable extreme ultraviolet frequency comb generation Pinkert, T. J.; Kandula, D. Z.; Gohle, C. ...
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC)
Conference Proceeding
Frequency comb lasers have led to great advances in fields such as precision spectroscopy, optical atomic clocks, and attosecond science. We transfer the remarkable precision of frequency combs to ...extreme ultraviolet (XUV) wavelengths by parametric amplification and high-harmonic generation (HHG) of two subsequent Ti:Sapphire comb laser pulses. As a result a pair of phase-locked extreme ultraviolet pulses is generated, which can be used directly for precision spectroscopy without the need for an additional spectroscopy laser. Viewed in the frequency domain, the spectrum of the upconverted pulse sequence in the XUV still resembles a frequency comb, but now in the form of a cosine-modulated spectrum. From a time domain perspective, excitation with phase-locked pulses is a form of Ramsey excitation.
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