3.3–3.7 μm Nested cavity OPO pumped by an amplified micro-laser for portable DIAL

Abstract

The detection, identification and quantification of various air pollutants are key issues in several fields of investigation such as environmental and industrial surveillance, security, or biology. These applications require the development of specific optical sensors. For remote detection of green-house and industrial gases, it is necessary to develop compact, portable, low cost and user-friendly differential absorption LIDAR (DIAL) systems, which are able to respond to the demanding specifications for multi-species atmospheric gas detection.The 3.3 -3.7 μm range is of high interest to perform DIAL measurements since most gas species display strong absorption lines in this range. Moreover, to be able to detect several species with a high sensitivity, the source has to display both a wide spectral tunability and a narrow linewidth (single frequency operation).Nested Cavity optical parametric oscillators (NesCOPOs) have been proven to be performing tools to achieve the single frequency operation and fine frequency control needed for gas sensing applications. Thanks to the low operation threshold of the NesCOPO (few μJ), we have previously demonstrated micro-laser pumping of the device in nanosecond regime [2], and performed Integrated Path DIAL (IPDIAL) measurements on atmospheric CO 2 at 4.2 μm with a 30 m range.Here we present a new transmitter, designed to allow us to demonstrate improved IPDIAL performances. Indeed, such a new transmitter is designed to respond to the need for detection of other species (especially CH4), with an extended range of operation (> 100m). It is based on a 1.064μm pump source, which is a fiber amplified microlaser achieving single frequency, 8 ns pulse duration and a 200μJ per pulse energy level at a repetition rate of 2 kHz with an excellent beam quality (M²<1,08). The laser is based on a co-propagative MOFA architecture. The seed master oscillator is a microlaser specially tailored by Teem photonics to produce a single frequency 1.064μm signal at 15μJ, 8ns per pulse at 2kHz. Such microlaser have already been successfully used to pump directly NesCOPOs in the past [3]. The high gain amplifier is a Taranis, Nd doped -YAG fiber module from Fibercryst. Such a fiber amplifier had been already tested successfully to amplify sub nanosecond passively Qswitched microlasers [4]. The type 0 PPLN NesCOPO device allows 3.3 -3.7 μm coverage. First characterisations (Fig 1) of the transmitter show a threshold of operation around 20 μJ at 3.7 μm. The beam quality is compatible with IP-DIAL measurements. Single frequency operation was demonstrated with a side mode suppression ratio better than 30 dB. These performances are compliant with a sensitive IPDIAL measurement.

Remote Sensing of Atmospheric Methane with IR OPO Lidar System

“…Advances in research and manufacture of nonlinear optical crystals make it possible to create new gas analysis systems [1][2][3] and thereby expand the possibilities of remote monitoring of the environment.…”