OPO technique has the advantage of producing pulsed mid-infrared radiation with broad wavelength coverage which makes up for the absence laser emission in certain band of frequencies. The 2.6 micrometer band lasers have many potential applications in fields such as industrial pollution sources monitoring [1,2].Moreover, KTA crystal features large non-linear optical and electro-optical coefficients and low crystal loss in the wavelength range 2.6-3.2 μm; high nonlinear coefficient; high optical damage threshold; low temperature sensitivity. KTA is also non-hygroscopic, and offers the possibility of critical phase matching with a high value of dλ/dθ which results in a narrow free running linewidth [3,4]. It has found wide applications in optical parametric oscillation/ amplification (OPO/OPA), and electro-optical Qswitching involving MIR wavelengths [5]. In this paper, we report on an intra-cavity pumped self-cascaded OPO-based on the NCPM KTA-OPO design [6,7] for the generation of a 2.59 μm high laser peak power.
We present a novel laser-pulsed shutter constructed by combining a solid-state pulsed high-voltage gas pre-ionizer and a CO2-TEA laser beam self-generated plasma. This cascaded electro-optical modulator produces 60 ns laser output pulses with less than 7 ns jitter leading to high output energy stability. No pulse recovery occurs after the laser pulse is clipped. The high voltage pulse-based pre-ionization module also has the advantage of being automatically integrated into the pulse-forming network of the laser discharge circuit.
A Dual differential absorption LIDAR (DIAL) based on two stage tandem OPO midinfrared (IR) tunable Optical Parametric Oscillator (OPO) has been developed and characterized. The first OPO stage, built around a nonlinear KTP crystal in an unstable resonator, produces 40 mJ of 1.57 μm radiation when pumped by a Q-switched Nd:YAG laser. Silver gallium selenide (AgGaSe2) crystal forms the OPO second stage which generates 0.9 mJ of Idler peak energies within 5.0 to 11.0 μm tuning region with typical spectral bandwidth values of the mid-IR radiation of 7-8 cm-1 which is well-matched with many complex molecules in the atmosphere which have bandwidths larger than 15 cm-1. The receiver is composed of a gold-plated primary mirror of a 300 mm forms the Cassegrain telescope, two channel detection system and control and amplifying electronics. Preliminary path-averaged ammonia concentration measurements are presented and analyzed.
An extra-laser cavity CO2-TEA laser pulse clipper using gas breakdown techniques for high spatial resolution material processing and shallow material engraving and drilling processes is presented. Complete extinction of the nitrogen tail, that extends the pulse width, is obtained at pressures from 375 up to 1500 torr for nitrogen and argon gases. Excellent energy stability and pulse repeatability were further enhanced using high voltage assisted preionized plasma gas technique. Experimental data illustrates the direct correlation between laser pulse width and depth of engraving in aluminum and alumina materials.
High stability and energy-efficient TE–CO2 laser pulse clipper using gas breakdown techniques for high spatial resolution chemical plume detection is presented. The most dominant time constant, attributed to TE–CO2 unclipped laser pulses, is its nitrogen tail which extends for several microseconds beyond the gain-switched spike. Near-field scattered signal, produced by unclipped laser pulses, interferes with the weak signal backscattered from the long range and far field atmospheric aerosols which ultimately degrades the range resolution of LIDARS to some hundreds of meters. Short laser pulses can be obtained by various techniques such as mode locking, free induction decay, pulse slicing with electro-optic switched. However, output pulses from these require further amplification for any useful application due to their very low energy content. This problem is circumvented in this work by the use of a plasma clipper that achieves high range-resolved remote sensing in the atmosphere. Complete extinction of the nitrogen tail is obtained at pressures extending from 375 up to 1500 Torr for nitrogen and argon gases and approximately 105, for helium. Optimum pressures for helium, argon, and nitrogen, that provide the best stability of the transmitted energy and complete extinction of the nitrogen tail, are identified. Excellent range resolutions can be achieved with TE–CO2 laser-based LIDAR systems. Clipped laser pulses are also field tested.
The pulse from a transversely excited atmospheric CO2 laser consists of a sharp spike followed by a long, drawn out tail
region spanning about 2-5 μs caused by the nitrogen gas in the laser cavity. The nitrogen tail is undesirable in many
applications because it decreases the average power of the laser pulse. High stability and energy-efficient laser-induced
plasma shutter to clip the nitrogen tail of CO2-TEA based DIAL is built. Optimum shutter gases pressures and laser
breakdown intensities are reported. Clipped laser pulses are also field tested.
CO2-laser DIAL ozone integrated measurements were performed in Madrid City. The results showed a
dependence of ozone on UVB radiation, abundance of vehicle generated NOX's and hydrocarbons. An average
decrease of 12.0 ± 1.2 % of the intensity of vehicle traffic resulted in a lowering the ozone load by almost 14.0 ±1.4 %. Moreover, measurements of atmospheric ethylene, as a hydrocarbon representative and its relation with
ozone, were performed. Ozone showed the same behaviour namely, a slow increase then reached a maximum at
around 15:00 and back to 40-50 ppb level. The new data can stimulate the development of new local models to
understand the dynamic underlying urban pollution.
Ethylene has been monitored with a single-ended CO2-TEA laser-based DIAL system using a topographic target. The direct correlation between ozone concentration and ethylene/NOx ratio were demonstrated. Our work brings an additional confirmation of concurrent VOC/NOx and NOx-limited regimes in the generation of excess ozone.
Long-path ozone integrated measurements with a CO2-laser DIAL system were performed in Madrid City during the 'vehicle-free' day. The results showed a strong correlation between human activity and ozone photochemical generation. The ozone concentration follows, even quantitatively, the same trend of the overall traffic intensity as long as both the UVB radiation and NO2 are present. An average decrease of 12.3 ±1.2 % of the intensity of vehicle traffic during the 'free-vehicle' day resulted in a lowering the ozone burden by almost 14.4 ± 1.4 % . This new type of information can stimulate the development of local models to understand the dynamic underlying urban pollution. The results indeed show the effectiveness of such a measure as to reduce the ozone burden on human and plants health.
In the present work, an IR lidar-dial technique was used to monitor ozone concentration in Madrid urban atmosphere. Interestingly, it was found an unusual increase of ozone concentration due to heavy traffic conditions accompanying the holiday rush despite the prevailing low photochemical activity. Consequently, the usual daily ozone profile shifts towards late hours. A direct and quantitative correlation between ozone pollution and human activity such as the excess of vehicle traffic accompanying summer holidays departures from Mdrid City was observed. This new type of information can stimulate the development of local models to understand the dynamic underlying urban pollution.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.