Development of continuous-wave pump-enhanced optical parametric oscillators and their application to photo-thermal spectroscopy

  • Jack Thomas

Student thesis: Doctoral Thesis (DEng)


The development of both a spectrally tunable radiation source and a sensitive detection transducer for spectroscopic applications are described in this thesis. The emission source is an optical parametric
oscillator operating in the continuous-wave regime with a pump-enhanced singly-resonant architecture
and involves the separate development of two constituent parts: A continuous-wave pump laser
operating at 1064 nm based on neodymium-doped crystals focused on achieving high power whilst
maintaining single-frequency operation; and a split-ring pump-enhanced optical parametric oscillator
operating from this pump source focused on fine-tuning in mode-hops. This source was capable of
coarsely tuning in the mid-infrared over 3 – 4 μm with an average of 140 mW of power with the ability of
automated mode-hop tuning continuously over 90 cm⁻¹ in 0.07 cm⁻¹ steps. The detection transducer is
based upon photo-thermal interferometric spectroscopy which employs a phase-sensitive method to
detect the heating of a gas sample under radiation from the appropriately tuned source. Utilisation of a
spectrally-independent probe beam permits samples with strong absorption features in the mid/deep-infrared
to be examined whilst utilising the low-cost, high-sensitivity photodetectors in the visible/near-infrared
region. This work implements both a Mach-Zehnder and a Sagnac interferometer, where the
latter holds the potential to minimise the effects of the environment and simplify the associated
experimental steps by removing stabilising electronic circuitry. Combined utilisation of this transducer
alongside the excitation source has demonstrated an ability to detect the presence of ethane down to
100 parts-per-billion. Further development considered the interferometer inherent in photo-thermal
spectroscopy, where this provides an avenue for employing optical squeezing techniques to increase the
ultimate sensitivity of this technique. Construction of a squeezed light generator to use as a probe beam
based on second-order nonlinearity has additionally been attempted in this work and has been shown to
exhibit anti-squeezing characteristic behaviour.
Date of Award28 Jun 2021
Original languageEnglish
Awarding Institution
  • University of St Andrews
SupervisorCameron Francis Rae (Supervisor), David James Mark Stothard (Supervisor) & Malcolm Harry Dunn (Supervisor)


  • Optical parametric oscillator
  • Photo-thermal interferometric spectroscopy
  • Mid-infrared spectroscopy
  • Continuous mode-hop tuning
  • Sagnac interferometer
  • Single-frequency sources
  • Mid-infrared sources
  • Gas spectroscopy
  • Squeezed light generator

Access Status

  • Full text embargoed until
  • 10th February 2023

Cite this