Shinobu Ohara

Performance Characteristics of Narrow Linewidth Fiber Laser Pumped Mid-IR Difference Frequency Mixing Light Source for Methane Detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

Simultaneous Raman spectra measurement using power build-up cavity (PBC)

Raman spectroscopy using a simple external Power Build-up Cavity (PBC) pumped with a diode laser was demonstrated. The PBC is very simple configuration consisted of anti- reflection coated low power (10mW, (lambda) equals670nm) laser diode, Graded index (GRIN) lens, and extremely high finesse external cavity, where the beam intensity can reaches up to 100W intracavity beam. Such a high finesse external cavity could optimized parameter attribute to high spectral brightness mostly suitable for a compact Raman light source without any sophisticated temperature and/or current injection control. PBC pumped Raman spectrum was measured by an optical fiber coupled optical multi-channel analyzer (OMA). The Raman signal from intracavity beam was imaged on the optical fiber by two focusing lenses (fequals38mm, 50mm) located in perpendicular to the optical axis. Stokes Raman spectra of N2 and O2 of gas mixture were simultaneously measured with real time operation, approximately.

Yb fiber laser pumped mid-IR source based on difference frequency generation and its application to methane detection

Summary form only given. A cw narrow-linewidth tunable mid-IR coherent source has become a useful tool for trace gas detection since almost all gases exhibit fundamental rovibrational absorption lines with high absorption strength in the mid-IR. This particular source is obtained by a difference frequency generation technique which is that two near IR laser pump sources (/spl lambda//sub 1/, /spl lambda//sub 2/) are mixed to generate mid-IR (/spl lambda//sub 3/=(1//spl lambda//sub 1/-1//spl lambda//sub 2/)/sup -1/) in a quasi-phase-matched nonlinear optical crystal such as a periodically poled LiNbO/sub 3/ in single-pass geometry. Such a spectroscopic source can operate at room temperature with single spatial mode, single frequency and tunable in wide frequency region without mode hop. This paper reports an experimental study of a fiber laser (1063.8 nm) based mid-IR generation to detect methane.