Phase-Locked High-Order Harmonic Sources

Zerne, R; Altucci, C.; Bellini, Marco; Gaarde, Mette B.; Hänsch, Theodor W.; L’Huillier, Anne; Lyngå, C; Wahlström, Claes‐Göran

doi:10.1103/physrevlett.79.1006

Cited by 109 publications

(56 citation statements)

References 13 publications

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“…The fringe patterns show a high stability, only slightly disturbed by residual mechanical vibrations in the interferometer, as well as a high robustness against differences in intensities in the two pump pulses. These observations confirm the results presented in our previous paper [9], and extend them to laser pulses of significantly higher intensity and shorter duration, as well as to shorter generated wavelengths.…”

Section: (Received 19 December 1997)supporting

confidence: 81%

“…However, the temporal coherence which is a very fundamental property, has gone largely unexplored so far, except for some spectral measurements [8]. Recently, we have shown that two spatially separated sources of high harmonic radiation created by the same laser pulse are phase locked [9] and lead to interference fringes when superposed in the far field. That experiment, however, did not shed light on the temporal coherence of the harmonic radiation, since the two harmonic pulses were superposed in time.…”

Section: (Received 19 December 1997)mentioning

confidence: 99%

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Temporal Coherence of Ultrashort High-Order Harmonic Pulses

et al. 1998

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Section: (Received 19 December 1997)supporting

confidence: 81%

Section: (Received 19 December 1997)mentioning

confidence: 99%

Temporal Coherence of Ultrashort High-Order Harmonic Pulses

et al. 1998

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“…To reach wavelengths below 120 nm in the extreme ultraviolet or even x rays, high harmonic generation (HHG) has to be employed requiring nonlinear interaction at much higher intensities in the nonperturbative regime [15]. That HHG can be phase coherent to some degree is known [15][16][17], and recently XUV light has been generated based on upconversion of all pulses of a comb laser at full repetition rate [18][19][20][21]. However, no comb structure in the harmonics has been demonstrated in the XUV, nor had these sources enough power to perform a spectroscopic experiment.…”

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confidence: 99%

Extreme Ultraviolet Frequency Comb Metrology

et al. 2010

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The remarkable precision of frequency-comb (FC) lasers is transferred to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), a frequency region previously not accessible to these devices. A frequency comb at XUV wavelengths near 51 nm is generated by amplification and coherent upconversion of a pair of pulses originating from a near-infrared femtosecond FC laser. The phase coherence of the source in the XUV is demonstrated using helium atoms as a ruler and phase detector. Signals in the form of stable Ramsey-like fringes with high contrast are observed when the FC laser is scanned over P states of helium, from which the absolute transition frequency in the XUV can be extracted. This procedure yields a 4 He ionization energy at h Â 5 945 204 212ð6Þ MHz, improved by nearly an order of magnitude in accuracy, thus challenging QED calculations of this two-electron system. Mode-locked frequency-comb (FC) lasers [1,2] have revolutionized the field of precision laser spectroscopy. Optical atomic clocks using frequency combs are about to redefine the fundamental standard of frequency and time [3]. FC lasers have also vastly contributed to attosecond science by providing a way to synthesize electric fields at optical frequencies [4], made long distance absolute length measurements possible [5], and have recently been employed to produce ultracold molecules [6]. FC based precision spectroscopy on simple atomic systems has provided one of the most stringent tests of bound state quantum electrodynamics (QED) as well as upper bounds on the drift of fundamental constants [7]. Extending these methods into the extreme ultraviolet (XUV, wavelengths below 100 nm) spectral region is highly desirable since this would, for example, allow novel precision QED tests [8].Currently the wavelength range below 120 nm is essentially inaccessible to precision frequency metrology applications due to a lack of power of single frequency lasers and media for frequency up-conversion. Spectroscopic studies on neutral helium using amplified nanosecond laser pulses [9,10] are notoriously plagued by frequency chirping during amplification and harmonic conversion which limits the accuracy. These kind of transient effects can be avoided if a continuous train of high power laser pulses (produced by a FC) can be coherently up-converted. This would transfer the FC modes, at frequencies f n ¼ f CEO þ nf rep , where f CEO is the carrier-envelope offset frequency, f rep is the repetition frequency of the pulses, and n an integer mode number, to the XUV. Similar to what was shown in the visible [11,12], the up-converted pulse train could be used to directly excite a transition, with each of the up-converted modes acting like a single frequency laser.By amplification of a few pulses from the train, and producing low harmonics in crystals and gasses, sufficient coherence has been demonstrated down to 125 nm to perform spectroscopic experiments [13,14]. To reach wavelengths below 120 nm in the extreme ultraviolet or even x rays, high harmonic generati...

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“…Therefore, a higher degree of phase coherence is expected in this case. Experimentally, this has been verified for individual harmonics (Zerne et al 1997) by inducing spatial interference between two HHG beams, as shown in Figure 31. For this demonstration, 35 ps pulses from a normal mode-locked 1064 nm laser (not a frequency comb) were split in two and individually focused side by side to ≈ 10 13 W cm −2 in a gas jet.…”

Section: Upconversion Of Frequency Comb Lasersmentioning

confidence: 84%

Precision Laser Spectroscopy in the Extreme Ultraviolet

Eikema

Ubachs

2011

Handbook of High‐resolution Spectroscopy

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Techniques for the production of short wavelengths in the extreme ultraviolet wavelength range are described, spanning low‐order harmonic generation in the perturbative regime for narrow bandwidth XUV production to the plateau‐regime with the three‐step collisional model for the generation of high harmonics with broadband ultrafast pulses. In addition, the intermediate regime is discussed for pulses of 300 ps duration, as well as the regime of harmonic conversion based on continuous wave lasers aiming at the production of coherent Lyman‐α radiation. Applications of XUV sources in the frequency domain typically rely on the production of XUV‐light from narrowband Fourier‐transform‐limited pulses for recording high‐resolution spectra. Alternatively, harmonically upconverted pulses of ultrashort duration (with inter‐pulse coherence) can be used for spectroscopic studies in the time and frequency domain (such as direct frequency comb spectroscopy techniques). Examples of both approaches for atomic and molecular spectroscopy are discussed at some length. For precision metrology on atomic systems, a focus is put on the Lamb shift determination in the He ground state. In the realm of molecular spectroscopy, predissociation phenomena in the nitrogen molecule are highlighted, with relevance for dissociation processes occurring in the upper layers of the Earth atmosphere. Similar predissociation phenomena in carbon monoxide are also treated in some detail, in this case with relevance for the chemistry in interstellar clouds. Precision XUV spectroscopy of molecular hydrogen is discussed as well, as it relates to the possibility of detecting a variation of the proton–electron mass ratio on a cosmological time scale. In the last section, applications of direct frequency comb spectroscopic techniques at short wavelengths are explained and prospects are given for using these techniques at extreme ultraviolet wavelengths.

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Phase-Locked High-Order Harmonic Sources

Cited by 109 publications

References 13 publications

Temporal Coherence of Ultrashort High-Order Harmonic Pulses

Temporal Coherence of Ultrashort High-Order Harmonic Pulses

Extreme Ultraviolet Frequency Comb Metrology

Precision Laser Spectroscopy in the Extreme Ultraviolet

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