L. Gianfrani

Frequency-comb-referenced quantum-cascade laser at 4.4 μm

We report what we believe to be the first absolute frequency measurement performed using a quantum-cascade laser (QCL) referenced to an optical frequency comb synthesizer (OFCS). A QCL at 4.43 microm has been used for producing near-infrared radiation at 858 nm by means of sum-frequency generation with a Nd:YAG source in a periodically poled lithium niobate nonlinear crystal. The absolute frequency of the QCL source has been measured by detecting the beat note between the sum frequency and a diode laser at the same wavelength, while both the Nd:YAG and the diode laser were referenced to the OFCS. Doppler-broadened line profiles of (13)CO(2) molecular transitions have been recorded with such an absolute frequency reference.

Quantitative diode laser absorption spectroscopy near 2 μm with high precision measurements of CO2 concentration

A diode laser sensor was developed to measure CO2 concentration using absorption spectroscopy at 2 μm. The simplicity of the optical setup and detection electronics makes this spectrometer very compact and well suited for field studies, while the use of optical fibers enables one to probe remote environments. This sensor is capable of providing absolute measurements, with the concentration being inferred from the directly measured absorption spectra, without using calibration cells. This ensures versatility as well as widespread applicability, and a linear response over a large dynamic range. Its analytical capabilities were carefully tested by a large variety of measurements, also with use of a certified CO2/air mixture. The precision of mixing ratio retrievals was about 0.2% while the accuracy was 0.9% for measurements of ambient CO2 concentration. The spectrometer is also capable of providing high precision measurements of the water vapor concentration in ambient air. Specifically, simultaneous detecti...

Detection of H 2 O and CO 2 with distributed feedback diode lasers: measurement of broadening coefficients and assessment of the accuracy levels for volcanic monitoring

We reproduced the chemical-physical conditions of fumarolic emission at Phlaegrean Fields, Pozzuoli, Italy, and we measured the CO(2) and H(2)O concentrations using an absorption spectrometer based on two distributed feedback laser diodes at wavelengths of 1.578 and 1.393 microm. We discuss the accuracy levels of the different methods used. Furthermore, we measured the broadening coefficients for H(2)O (self-broadening, 28.2 +/- 0.6 MHz/Torr; CO(2) broadening, 6.0 +/- 0.4 MHz/Torr) and CO(2) (self-broadening, 3.2 +/- 0.1 MHz/Torr; H(2)O broadening, 4.0 +/- 0.1 MHz/Torr). Using the present data, we evaluated a minimum detectable variation of 9% for H(2)O and 1% for CO(2).

Precision spectroscopy of NH 3 at 9.1 μm by a comb-referenced quantum cascade laser

Absorption spectroscopy of NH 3 at 9.1 μm is demonstrated with a quantum-cascade-laser absolutely referenced to a Tm-fiber frequency-comb. Highly-accurate spectroscopic parameters are retrieved by a multiple-line fitting approach applied to the spectral manifold.