Browsing by Subject "optical frequency comb"

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  • Ulvila, Ville; Vainio, Markku (2020)
    Optical frequency comb generation by continuous-wave-pumped cascaded quadratic nonlinearities (CQN) appears a promising alternative to well-established modelocked lasers, especially if access to the mid-infrared spectral region is needed. We report an experimental investigation of spectral properties of a CQN frequency comb, which is based on second-harmonic generation (SHG) and is pumped internally by a continuous-wave optical parametric oscillator. Our study focuses on SHG phase mismatch, which has drawn little attention in the previously reported CQN frequency comb research. The main observation of our study is that it is possible to improve spectral purity of the CQN frequency comb by adjusting the phase mismatch. In addition to the CQN process that generates a frequency comb in the near-infrared region, our experimental setup involves several other nonlinear processes. These processes lead to a composite comb, which extends from visible to mid-infrared.
  • Metsälä, M. (2018)
    Optical spectroscopy can be used for trace-level gas analysis in different applications, including exhaled breath research. A common approach is the targeted on-line, real-time analysis of small molecules (two to five atoms). Currently, the methodology is normally used for the detection of single analytes at trace levels, or two to three species at most at the same time. The main limitation preventing sensitive multi-species detection has been the limited fast scanning range of the lasers used as light sources. This limitation is currently being eliminated by the availability of optical frequency combs (OFC) which offer wide spectral bandwidths and the benefits of a laser-type light source. Recent advances in mid-infrared OFC technology allow measurements in the so-called molecular fingerprint region of the electromagnetic spectrum, where many molecules have strong fundamental vibrational transitions that enable sensitive detection. Several technical hurdles remain to be overcome, but if these problems can be solved laser absorption spectroscopy has the potential to challenge mass spectrometry in on-line multi-species trace gas analysis.