Phase-Coherent Frequency Combs in the Vacuum Ultraviolet via High-Harmonic Generation inside a Femtosecond Enhancement Cavity

JILA, National Institute of Standards and Technology and University of Colorado, Boulder, 80309-0440, USA.
Physical Review Letters (Impact Factor: 7.51). 06/2005; 94(19):193201. DOI: 10.1103/PhysRevLett.94.193201
Source: PubMed


We demonstrate the generation of phase-coherent frequency combs in the vacuum utraviolet spectral region. The output from a mode-locked laser is stabilized to a femtosecond enhancement cavity with a gas jet at the intracavity focus. The resulting high-peak power of the intracavity pulse enables efficient high-harmonic generation by utilizing the full repetition rate of the laser. Optical-heterodyne-based measurements reveal that the coherent frequency comb structure of the original laser is fully preserved in the high-harmonic generation process. These results open the door for precision frequency metrology at extreme ultraviolet wavelengths and permit the efficient generation of phase-coherent high-order harmonics using only a standard laser oscillator without active amplification of single pulses.

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Available from: Jun Ye, Mar 26, 2015
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    • "For some applications a geometrical access along the optical axis is desirable, e.g. if there are no dichroic mirrors available for the given wavelengths. The particular problem that motivated the present work is the output coupling of high harmonics generated in a gas jet near the focus of a femtosecond enhancement resonator [4] [5]. Depending on the application, geometrical output coupling through an opening in a resonator mirror can be advantageous compared to alternative methods: there is no additional optical element in the resonator and hence no additional dispersion, nonlinearity, bandwidth limitation or polarization discrimination for the fundamental radiation, and the harmonics are not angularly dispersed. "
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    ABSTRACT: We describe a novel method for providing geometrical on-axis access to an optical enhancement resonator through an on-axis aperture at one of its mirrors. A superposition of transverse modes in a stable degenerate resonator is used to form a field distribution which avoids the aperture and therefore exhibits small loss. Upon propagation in the resonator the modes acquire a different phase, and an on-axis intensity maximum is formed at a different position. We call this a quasi-imaging resonator, because it is related to imaging in the sense that a hole in the field distribution, exacted by the aperture, is reproduced after a resonator round trip.
    Preview · Article · Feb 2015 · Journal of optics
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    • "An alternative method capable of achieving significantly higher repetition rates with suitable pulse energies uses a femtosecond enhancement cavity (fsEC) [19] [20], illustrated in figure 1. With this technique, the output of a mode-locked oscillator is coupled to a high-finesse cavity. "
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    ABSTRACT: We report on recent developments in tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC). The XUV frequency comb is produced via HHG at the full repetition rate of the mode-locked oscillator (typically >50 MHz), inside a passive enhancement cavity with an enhancement of a few hundred. Several technical challenges have recently been resolved, which have led to an increase in the generated photon flux in the XUV (10^14 photons/sec), and a substantial improvement in the operating time of these sources. XUV sources based on fsECs are now able to perform direct frequency comb spectroscopy with MHz precision in atomic systems at wavelengths down to 60 nm. Ongoing research is aimed at determining the ultimate frequency stability of these new XUV frequency comb sources. XUV fsEC sources are also promising for some applications that are typically performed with XUV light at advanced light sources. These applications include electronic structure of quantum material systems, such as angle-resolved photoemission spectroscopy (ARPES), size metrology of nano-aerosol particles, and potentially velocity map imaging for studies of chemical physical problems. In this talk, we present a brief introduction to XUV frequency comb sources and the technical challenges that have been overcome to achieve the current performance levels. We will also discuss our progress on ARPES experiments with a fsEC XUV source and our efforts toward increasing the energy resolution of the produced harmonics. Finally, we describe ongoing efforts to further increase the maximum photon energy and photon flux generated, and subsequently delivered to an experiment by fsEC XUV sources.
    Full-text · Article · Oct 2012
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    • "Two approaches have been demonstrated for achieving the intensity threshold for HHG directly from ∼100 MHz repetition rate oscillators. In the first approach, the femtosecond laser pulses are coupled to an external cavity that contains the nonlinear medium (noble gas) [4] [9] [10]. The finesse of these cavities is limited to ∼1000 because the bandwidth of the cavity must support the femtosecond pulses that circulate inside. "
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    ABSTRACT: We predict and investigate the emission of high-order harmonics by atoms that cross intense laser hot spots that last for a nanosecond or longer. An atom that moves through a nanometer-scale hot spot at characteristic thermal velocity can emit high-order harmonics in a similar fashion to an atom that is irradiated by a short-duration (picosecond-scale) laser pulse. We analyze the collective emission from a thermal gas and from a jet of atoms. In both cases, the line shape of a high-order harmonic exhibits a narrow spike with spectral width that is determined by the bandwidth of the driving laser. Finally, we discuss a scheme for producing long-duration laser hot spots with intensity in the range of the intensity threshold for high-harmonic generation. In the proposed scheme, the hot spot is produced by a long laser pulse that is consecutively coupled to a high-quality micro-resonator and a metallic nano-antenna. This system may be used for generating ultra-narrow bandwidth extreme-ultraviolet radiation through frequency up-conversion of a low-cost compact pump laser.
    Full-text · Article · Jun 2012 · New Journal of Physics
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