Nilesh J. Vasa

Multiwavelength distributed-feedback dye laser array and its application to spectroscopy

A multiwavelength, multistripe tunable laser array is proposed, and its application to absorption spectroscopy is demonstrated. Laser waveguides doped with Rhodamine 6 G dye were integrated on a plastic chip, and simultaneous output at different wavelengths was obtained by use of a distributed-feedback technique. A very low threshold of 3 muJ was attained, and spectrally narrowed output (<0.1 nm) was obtained. A scheme for digital spectroscopy is also proposed based on this laser array, and absorption spectroscopy of sodium atoms without wavelength scanning is demonstrated by use of a sodium-vapor cell.

Wide-wavelength-range operation of a distributed-feedback dye laser with a plastic waveguide

A compact distributed-feedback (DFB) dye laser with a plastic waveguide was developed. The DFB operation was attained by the interference of two pumping beams from a frequency-doubled pulsed Nd:YAG laser, and a wavelength range between 560 nm and 994 nm was continuously covered. The dye chip can instantaneously exchanged in any spectrum region. The threshold energy was decreased to the order of 100 µJ with the waveguide configuration. The maximum life of the dye chip was 106 shots.

Improvement of Fluorescence Characteristics of Er3+-Doped Fluoride Glass by Ce3+ Codoping

The fluorescence characteristics of Ce3+:Er3+ codoped fluoride glass are reported. It is observed that the decay rate of the 4I11/2 state of Er3+ increased by increasing the Ce3+ concentration. Further, the branching ratio for the transition from the 4I11/2 state to the 4I13/2 state of Er3+ increased from 0.20 to 0.95 by codoping 6.0 mol% Ce3+ into Er3+-doped ZBLAN-H fluoride glass. As a result, the 1.55 ?m fluorescence quantum yield has been significantly improved.

COMPARATIVE STUDY OF SPECTRAL NARROWING OF A PULSED TI:SAPPHIRE LASER USING PULSED AND CW INJECTION SEEDING

We report a comparative study of a pulsed as well as continuous-wave (cw) injection seeding of a Ti:Sapphire laser pumped by aQ-switched frequency-doubled Nd3+:YAG laser for achieving narrow spectral bandwidth. The results have indicated that the Ti:Sapphire laser using either a pulsed or a cw injection seeding could achieve efficient energy extraction in a narrow spectral bandwidth. In the case of pulsed injection seeding, the injection energy required for the complete injection seeding critically depended upon the timing of the Ti:Sapphire laser with respect to the delayed onset of the slave laser. On the other hand, in the case of cw injection seeding, the spectral bandwidth of the Ti:Sapphire laser was efficiently narrowed down to approximately 0.01 cm−1 with an injection power of less than 1 mW. In both types of injection seeding, characteristics observed experimentally were compared with those obtained by a numerical simulation code based on the one-dimensional rate-equation model.

Differential absorption lidar at 1.67 μm for remote sensing of methane leakage

A differential absorption lidar (DIAL) for field monitoring of methane (CH4) leakage at a wavelength of 1.67 µm was developed. Compared with traditional DIAL systems for environmental monitoring, this system has a higher distance resolution (~15 m) for determining the leak position and a shorter detection range up to 500 m. First, considering appropriate design parameters, a theoretical simulation was performed to evaluate the sensitivity and the detectable range of the system. Based on the analytical simulation, a prototype DIAL system was constructed and the detection of CH4 which had leaked into the atmosphere was demonstrated. The CH4 leakage of 6000 ppmm at a distance of 130 m was successfully detected. The detection limit was 1000 ppmm. With the improvements in the light source and the detector system, the detectable boundary can be increased in the range from 90 to 540 m for a concentration of 1500 ppmm.

Superluminescent Diode-Based Multiple-Gas Sensor for NH

An approach of superluminescent light emitting diode (SLED)-based multiple-gas sensing (NH3 and H2O vapor) is proposed and demonstrated by using an absorption spectroscopy technique for emission monitoring (DeNOx process) applications. Such process normally occurs at temperature range of 250-400°C where significant interference effect due to H2O vapor is expected. Hence, measuring multiple gases and eliminating cross-interference effect is of great importance in sensing trace gases. In this study, an SLED-based sensor with center emission wavelength of 1530-nm region is chosen to measure the concentrations of pure NH3 and H2O vapor by probing its overtone and combination bands present in this region. Detection limit for the NH3 gas accounted in the case of aqua-ammonia (undiluted) is estimated to be 120 ppm ·m. A novel approach of introducing an open-space etalon in the path of the SLED beam is also proposed and demonstrated for adequate isolation from interfering species and improving the detection limit. By using an etalon with a free spectral range of 104 GHz and tuning it to appropriate wavelength, detection limit of about 22 ppm·m is attained for NH3 gas sensing in the presence of H2O vapor.

_{\bf 3}

A spectrally narrowed widely tunable Ce/sup 3+/: Er/sup 3+/-codoped fluorozirconate (ZBLAN) fiber laser with a continuous-wave laser diode pumping at 975-nm pumping is demonstrated. Wide tunable range over 120 nm (1490-1610 nm) is attained by using a diffraction grating combined with a tuning mirror in the Ce/sup 3+/: Er/sup 3+/-ZBLAN fiber laser cavity. Rate-equation model analysis shows that the tunable range can expand further by using a wavelength-dependent reflectivity cavity mirror.

and H

A novel approach of an optical second-harmonic generation (SHG) technique combined with an electro-optic effect is proposed for measuring an impulse electric field. The experimental measurements combined with theoretical estimates show that even though the temperature control is a critical requirement, the SHG technique with nonlinear, electro-optic crystals, such as MgO:LiNbO3 and KTiOPO4, can be effectively used for electric field measurements by utilizing the phase matching condition.

_{\bf 2}

In this paper, a novel method of the dual-wavelength (laser-induced breakdown spectroscopy LIBS) technique using a single laser system is proposed and demonstrated. Experiments are performed using a pulsed Nd3+ : YAG laser with a pair of 355–1064 nm and also with 532–1064 nm. The shorter wavelength laser is used for ablation and plasma formation, and the fundamental wavelength (1064 nm) is used for plasma re-excitation. The proposed dual-wavelength LIBS technique is used for lunar simulant samples under different ambient pressure conditions. Various characteristic parameters, such as the emission line-intensity enhancement, plasma temperature, lifetime and plasma area, are studied. Experimental studies clearly showed the emission line-intensity enhancement up to a factor of 3. Emission lifetime showed a longer sustained emission with an increase of up to 33% for the dual-wavelength approach. A theoretical simulation based on the hydrodynamic equations is also performed for dual-wavelength ablation and re-excitation. The estimated plasma temperature and ablation plume-front velocity clearly showed an increase in dual wavelength, which is in agreement with the experimental results.

O Vapor Monitoring

A Cr(3+):LiSAF laser oscillator self-injection locked by an externally coupled fiber grating was constructed. Single-mode operation in a Cr(3+):LiSAF laser was obtained by use of a 67%-ref lectivity fiber grating that was fabricated with a holographic technique in which a narrow-band KrF UV laser exposure was used. This configuration permits the use of a fiber grating with optimum ref lectivity for efficient single-mode operation.