Methane sensing at 3.4μm using chirped laser dispersion spectroscopy with DFG source

M. Nikodem, K. Krzempek, G. Plant, K. Abramski, Gerard Wysocki

Research output: Contribution to conferencePaper

1 Scopus citations

Abstract

Laser spectroscopy is a powerful tool for quantitative chemical detection. Recently we have introduced chirped laser dispersion spectroscopy (CLaDS), technique that is particularly well-suited for remote open-path gas sensing [1]. In CLaDS a laser beam containing multiple waves of different frequencies is transmitted through a measured sample. Subsequently the beam is focused onto a square-law photodetector which measures heterodyne beatnote between the waves. As the frequencies of these waves are synchronously chirped across the target transition, their propagation is altered due to frequency-dependent refractive index in the vicinity of the molecular resonance. This optical dispersion (proportional to molecular concentration) results in a change of the beatnote frequency, which can be retrieve though frequency demodulation of the photodetector signal [2]. Because the concentration of the target molecule is encoded into the beatonote frequency (not amplitude) CLaDS signal is immune to amplitude noise and transmission fluctuations. This is major advantage with respect to absorption-based techniques like direct absorption spectroscopy or WMS, and it is especially useful in remote sensing applications in which received optical power might fluctuate significantly. Recently we have developed CLaDS system that enables detection of CH4 using its overtone band at 1.65 μm [3]. The main advantage of the near-IR CLaDS system over previous mid-IR arrangements [1,2] is the access to off-the-shelf components such as high-speed telecom modulators. Fast modulators provide optimum frequency separation between the optical waves to achieve maximal CLaDS signal amplitude at atmospheric conditions (linwidths >1GHz). Here we present a system based on a differential frequency generation (DFG) that combines the strengths of both approaches giving: 1) an access to the fundamental mid-IR CH4 transitions, and 2) an advantage of optimum performance achieved with telecom-based components. A schematic diagram of this new optical set-up is shown in Fig. 1A. The signal beam is produced by a distributed feed-back laser diode (DFB LD) operating at 1.55 μm, which is frequency-chirped through triangular current modulation. A high-speed intensity modulator is used to create the multi-color beam (carrier + sidebands at ±ω) that is further amplified using Er-doped fiber amplifier (EDFA). The pump beam used for DFG is produced with another diode and is amplified with an Yb-doped fiber amplifier (YDFA). The two beams are combined using dichroic mirror and focused onto periodically poled lithium niobate (PPLN) crystal placed in the temperature stabilized oven. The mid-infrared radiation (∼100μW) is transmitted through a Ge filter, collimated using CaF2 lens and focused onto a fast TEC-cooled MCT photodetector (PD). The total sensing path of 170cm in the laboratory air (containing ∼2ppm of CH4) was used. The heterodyne beatnote at ω is frequency demodulated using an RF spectrum analyzer (Agilent N9010 EXA).

Original languageEnglish (US)
DOIs
StatePublished - Jan 1 2013
Event2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013 - Munich, Germany
Duration: May 12 2013May 16 2013

Other

Other2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013
CountryGermany
CityMunich
Period5/12/135/16/13

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering

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    Nikodem, M., Krzempek, K., Plant, G., Abramski, K., & Wysocki, G. (2013). Methane sensing at 3.4μm using chirped laser dispersion spectroscopy with DFG source. Paper presented at 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, Munich, Germany. https://doi.org/10.1109/CLEOE-IQEC.2013.6801188