RESUMEN
A scanning differential absorption lidar (DIAL) instrument for identification of carbon dioxide leaks at carbon sequestration sites has been developed and initial data has been collected at Montana State University. The laser transmitter uses two tunable discrete mode laser diodes operating in the continuous-wave mode with one locked to the online absorption wavelength and the other operating at the offline wavelength. Two in-line fiber optic switches are used to switch between online and offline operation. After the fiber optic switch, an acousto-optic modulator is used to generate a pulse train used to injection seed an erbium-doped fiber amplifier to produce eye-safe laser pulses with maximum pulse energies of 66 µJ, a pulse repetition frequency of 15 kHz, and an operating wavelength of 1.571 µm. The DIAL receiver uses a 28 cm diameter Schmidt-Cassegrain telescope to collect that backscattered light, which is then monitored using a photomultiplier tube module operating in the photon counting mode. The DIAL has measured carbon dioxide profiles from 1 to 2.5 km with 60 min temporal averaging. Comparisons of DIAL measurements with a Licor LI-820 gas analyzer point sensor have been made.
RESUMEN
An all diode-laser-based micropulse differential absorption lidar (DIAL) laser transmitter for tropospheric water vapor and aerosol profiling is presented. The micropulse DIAL (MPD) transmitter utilizes two continuous wave (cw) external cavity diode lasers (ECDL) to seed an actively pulsed, overdriven tapered semiconductor optical amplifier (TSOA). The MPD laser produces up to 7 watts of peak power over a 1 µs pulse duration (7 µJ) and a 10 kHz pulse repetition frequency. Spectral switching between the online and offline seed lasers is achieved on a 1Hz basis using a fiber optic switch to allow for more accurate sampling of the atmospheric volume between the online and offline laser shots. The high laser spectral purity of greater than 0.9996 coupled with the broad tunability of the laser transmitter will allow for accurate measurements of tropospheric water vapor in a wide range of geographic locations under varying atmospheric conditions. This paper describes the design and performance characteristics of a third generation MPD laser transmitter with enhanced laser performance over the previous generation DIAL system.
RESUMEN
The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5 GHz and a finesse of 50.7 (312) at 532 nm (1064 nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.
RESUMEN
A biological detection scheme based on the natural foraging behavior of conditioned honeybees for detecting chemical vapor plumes associated with unexploded ordnance devices utilizes a scanning lidar instrument to provide spatial mapping of honeybee densities. The scanning light detection and ranging (lidar) instrument uses a frequency doubled Nd:YAG microchip laser to send out a series of pulses at a pulse repetition rate of 6.853 kHz. The scattered light is monitored to produce a discrete time series for each range. This discrete time series is then processed using an efficient algorithm that is able to isolate and identify the return signal from a honeybee in a cluttered environment, producing spatially mapped honeybee densities. Two field experiments were performed with the scanning lidar instrument that demonstrate good correlation between the honeybee density maps and the target locations.
RESUMEN
Two laser-based instruments for carbon sequestration site monitoring have been developed and tested at a controlled carbon dioxide (CO(2)) release facility. The first instrument uses a temperature tunable distributed feedback (DFB) diode laser capable of accessing the 2.0027-2.0042 microm spectral region that contains three CO(2) absorption lines and is used for aboveground atmospheric CO(2) concentration measurements. The second instrument also uses a temperature tunable DFB diode laser capable of accessing the 2.0032-2.0055 mum spectral region that contains five CO(2) absorption lines for underground CO(2) soil gas concentration measurements. The performance of these instruments for carbon sequestration site monitoring was studied using a newly developed controlled CO(2) release facility. A 0.3 ton CO(2)/day injection experiment was performed from 3-10 August 2007. The aboveground differential absorption instrument measured an average atmospheric CO(2) concentration of 618 parts per million (ppm) over the CO(2) injection site compared with an average background atmospheric CO(2) concentration of 448 ppm demonstrating this instrument's capability for carbon sequestration site monitoring. The underground differential absorption instrument measured a CO(2) soil gas concentration of 100,000 ppm during the CO(2) injection, a factor of 25 greater than the measured background CO(2) soil gas concentration of 4000 ppm demonstrating this instrument's capability for carbon sequestration site monitoring.
RESUMEN
An imaging lidar instrument with the capability of measuring the frequency response of a backscattered return signal up to 3.6 kHz is demonstrated. The instrument uses a commercial microchip frequency-doubled pulsed Nd:YAG laser with a 7.2 kHz pulse repetition rate, a pulse duration of less than 1 ns, and a pulse energy of greater than 10 microJ. A 15.2 cm commercial telescope is used to collect the backscattered signal, and a photomultiplier tube is used to monitor the scattered light. This instrument is designed for range- and angle-resolved optical detection of honeybees for explosives and land-mine detection. The instrument is capable of distinguishing between the scattered light from honeybees and other sources through the frequency content of the return signal caused by the wing-beat modulation of the backscattered light. Detection of honeybees near a bee hive and spatial mapping of honeybee densities near feeders are demonstrated.
RESUMEN
The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.
RESUMEN
We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise.
RESUMEN
We demonstrate stable operation of a diode-pumped cw Raman ring laser in diatomic hydrogen gas. Doppler-induced asymmetry between the the forward and the backward Raman gains leads to inherent unidirectional operation in the forward direction without intracavity optical elements. Use of the ring-cavity geometry dilutes the deleterious effects of thermal lensing and significantly reduces optical feedback to the pump laser.
RESUMEN
A diode-pumped, far-off-resonance cw Raman laser in H(2) with rotational Stokes emission is reported for the first time to our knowledge. The Raman laser can produce single-wavelength emission at either 830 nm (rotational Stokes) or 1180 nm (vibrational Stokes) depending on the frequency tuning of the pump laser. The mirrors for the rotational cw Raman laser are easier to produce; the laser also exhibits a wider continuous tuning range and is less sensitive to thermal effects than the previously studied vibrational Raman laser [Opt. Lett. 26, 426 (2001) and references therein].