We demonstrate path-integrated simultaneous concentration measurements of water, methane and ethane, measuring spectra across the 3.1–3.5-μm range using 0.05 cm-1 resolution Fourier-transform spectroscopy in-line with an ultrafast optical parametric oscillator and a simple, non-compliant target. Illumination spectra were extracted from a fitting procedure which simultaneously minimized the rms error between the experimental spectrum and a synthetic spectrum calculated from the envelope and a fitted mixture of PNNL or HITRAN absorbance data for water, methane and ethane. Simultaneous methane, ethane and water measurement at 30-m range were initially performed. Indoor measurements launched light from the OPO through a 20-cm-long gas cell containing a 1.5±0.15% ethane-in-air mixture. Light was reflected from a rough Al-foil target. Best-fit concentrations were determined to be 1.15% (water), 1860 ppb (methane) and 1.37 % (ethane). The methane background value is consistent with reported ambient levels. Respective water and ethane values were consistent with the ambient relative humidity. The second experiment demonstrated real-time methane emission measurement at 70-m range. A 2% methane:air mix was released for 100 seconds at a rate of 103 μgs-1 at a distance of 65 m from the OPO. The signal was recorded from a simple target of rough aluminum foil situated 70 m from the OPO, with the beam passing near the emission point. This work demonstrates our ability to extract concentration data from a single spectrum with no need for averaging, which provides a real-time and quantitative monitoring capability.
The development of femtosecond (fs) lasers has continued rapidly since the demonstration of fs Ti:Sapphire systems in 1989. Recent research has yielded lasers which offer greatly enhanced performance in all areas. In this document we describe the development of femtosecond lasers with electrical to optical efficiency > 14%, pulse repetition frequencies > 4GHz and compact and stable cavities. We further outline the use of such lasers for the generation of high power visible femtosecond pulses and their application within systems environments for ultrahigh speed data communications, ultrafast optical switching and optical analogue to digital conversion. We also describe progress in the development of femtosecond lasers based on both active and passive semiconductor quantum dot components.
We report a highly efficient diode-pumped femtosecond Yb:KYW laser having a compact three-element resonator that incorporates a prismatic output coupler. Near-transform limited pulses of 107fs duration at a centre wavelength of 1056nm are produced at repetition pulse frequency of 294MHz by utilising soft-aperture Kerr-lens mode locking. The femtosecond operation had a mode-locking threshold at a pump power of 250mW and the laser was tunable from 1042nm to 1075nm. The optical-to-optical conversion efficiency exceeded 50% in this femtosecond-pulse regime.
We demonstrate a highly efficient and low threshold passively mode-locked femtosecond Yb:KYW laser pumped by an InGaAs narrow-stripe laser diode and which incorporates a semiconductor saturable absorber mirror. Near-transform limited pulses of 123fs at 1047nm were produced at an average mode-locked power of 107mW for only 308mW of incident pump power. An optical-to-optical conversion efficiency of 35% was achieved and the corresponding electrical-to-optical efficiency exceeded 14%.