High resolution ZrF₄-fiber-delivered multi-species infrared spectroscopy

Abstract

Using coherent broadband mid-infrared light from a picosecond optical parametric oscillator we introduce a flexible, easy to use, high-resolution technique which can be utilized to conduct remote stand-off, or fiber delivered, multi-species spectroscopy in a spectroscopically cluttered environment. In particular, both narrow line-like and broad continuum-like species can be handled simultaneously. If only species with narrow line-like absorptions are present, this can be done without the need for an explicit reference spectrum. We demonstrate the approach by performing absorption spectroscopy of H2O, CH4, CH3OH and C2H7NO (MEA) at high optical resolution (≈0.033 cm−1) and via fiber delivery, opening the possibility of conducting multi-species spectroscopy in remote and hazardous environments. Spectral co-fitting of all absorption features and of the spectrum of the light-source provides a robust means of determining species concentrations, with detection limits of 290 ppb and 890 ppb obtained for CH4 and MEA respectively using a 10.5-m Herriott cell and 32 seconds measurement time.

GPU-Accelerated Full-Field Modelling of Highly Dispersive Ultrafast Optical Parametric Oscillators

“…We have demonstrated a GPU-accelerated OPO simulator that exploits high-level parallelism in order to solve the 𝜒 (2) nonlinear envelope equation over 1000× faster than a CPU-based approach, enabling studies of highly dispersive systems that are otherwise computationally inaccessible.…”

“…The NEE describes the evolution of the complex electric field envelope A(𝑧, 𝑡) = E(𝑧, 𝑡)𝑒 −𝑖 𝜔 0 𝑡+𝑖𝛽 0 𝑧 in a transparent dispersive medium with nonlinear susceptibility 𝜒 (2) , where E(𝑧, 𝑡) is the inverse Fourier transform of the positive components of the physical electric field E(𝑧, 𝜔), 𝜔 0 is a chosen reference frequency, and 𝛽 0 is the real-valued wavevector at 𝜔 0 . The NEE is written as [8]:…”

“…Optical parametric oscillators (OPOs) are one of the most versatile platforms for the generation of visible, near-and mid-infrared pulses, and have found widespread use in spectroscopy and imaging applications [1][2][3][4]. In its simplest form, the energy exchange between discrete pump (𝜔 𝑝 ), signal (𝜔 𝑠 ), and idler (𝜔 𝑖 ) frequencies in an OPO can be approximated using the coupled wave equations [5], which rely on the assumption that the pulse bandwidth is narrow with respect to the carrier frequency.…”

“…In contrast, ultrafast synchronously-pumped OPOs are broadband systems that display complex dynamics [6] and spectral structures [7] that cannot be described by this slowly-varying envelope approximation. These systems are more readily described by a 𝜒 (2) nonlinear envelope equation (NEE) [8], an analytical technique for studying ultra-broadband 𝜒 (2) interactions.…”

Mid-infrared optical parametric oscillation spanning 3.4–8.2 μm in a MgF2 microresonator

“…The mid-infrared (MIR) wavelength region is not only an atmospheric window with minimum attenuation, but also covers multiple absorption peaks for many kinds of atoms and molecules [1][2][3][4]. An optical parametric oscillator (OPO) composed of discrete and equally-spaced optical frequency components can act as an excellent multi-wavelength source with high fineness, leading to the improvement of acquisition rate and resolution for molecular spectroscopy [5][6][7]. The MIR OPO is particularly important for access to molecular fingerprints and thus provides a powerful tool for the chemical composition analysis in biochemistry, medicine, optical sensing and material science [8,9].…”