Recent studies of the iodine dissociation mechanism for COIL systems have prompted new investigations of the energy transfer kinetics of O2(b1Σ+). Additional motivation for these studies, and for investigation of the quenching of I* by O atoms, is derived from efforts to build non-chemical singlet oxygen generators. Discharge generators produce relatively high concentrations of O2(b) and O atoms. Dissociations of I2 by the reagent streams from these generators will follow different kinetic pathways than those that are most important when the flow from a chemical generator is used. To improve our understanding of conventional COIL systems, and gain insights concerning the dissociation kinetics that will be relevant for discharge driven COIL devices we have examined the quenching of O2(b) and O2(a) by I2, and the deactivation of I* by atomic oxygen. The primary findings are: (1) Quenching of O2(b) by I2 is fast (5.8x10-11 cm3 s-1) with a branching fraction of 0.4 for the channel O2(b)+I2→O2(a)+I2. (2) The quantum yield for dissociation of I2 by O2(b) is relatively high (>0.5) and (3) The upper bound for the rate constant for quenching of I* by O atoms is k<2x10-12 cm3 s-1.
Singlet oxygen generators for COIL devices that involve discharge or optical excitation are currently being investigated. These generators deliver relatively high yields of O2(b1Σ+) as the flows do not contain water vapor. In addition, discharge generators provide high concentrations of O atoms. Dissociation of I2 by the reagent streams from these generators will follow different kinetic pathways than those that are most important when the flow from a chemical generator is used. To provide a basis for understanding the dissociation kinetics that will be relevant for discharge and optically driven COIL devices we have examined the quenching of O2(b) and O2(a) by I2. Dissociation of I2 by atomic oxygen and I*+O quenching have also been investigated. The primary findings are: (1) Quenching of O2(b) by I2 is fast (5.8x10-11 cm3 s-1) with a branching fraction of 0.4 for the channel O2(b)+I2→O2(a)+I2. (2) Quenching of O2(a) by I2 is too slow (k<5x10-16 cm3 s-1) to be the initiation step in the I2 dissociation process. (3) O2(a) is generated when I2 is dissociated by O atoms. (4) The upper bound for the rate constant for quenching of I* by O atoms is k<5x10-12 cm3 s-1.
In this paper we summarize the results on the development of high power 1300 nm ridge waveguide Fabry-Perot and distributed-feedback (DFB) lasers. Improved performance of MOCVD grown InGaAsP/InP laser structures and optimization of the ridge waveguide design allowed us to achieve more than 800 mW output power from 1300 nm single mode Fabry-Perot lasers. Despite the fact that the beam aspect ratio for ridge lasers (30 degree(s) x 12 degree(s)) is higher than that for buried devices, our modeling and experiments demonstrated that the fiber coupling efficiency of about 75-80% could be routinely achieved using a lensed fiber or a simple lens pair. Fiber power of higher than 600 mW was displayed. Utilizing similar epitaxial structures and device geometry, the 1300 nm DFB lasers with output power of 500 mW have been fabricated. Analysis of the laser spectral characteristics shows that the high power DFB lasers can be separated into several groups. The single frequency spectral behavior was exhibited by about 20% of all studied DFB lasers. For these lasers, side-mode suppression increases from 45 dB at low current up to 60 dB at maximum current. About 30% of DFB lasers, at all driving currents, demonstrate multi-frequency spectra consisting of 4-8 longitudinal modes with mode spacing larger than that for Fabry-Perot lasers of the same cavity length. Both single frequency and multi frequency DFB lasers exhibit weak wavelength-temperature dependence and very low relative intensity noise (RIN) values. Fabry-Perot and both types of DFB lasers can be used as pump sources for Raman amplifiers operating in the 1300 nm wavelength range where the use of EDFA is not feasible. In addition, the single-mode 1300 nm DFB lasers operating in the 500 mW power range are very attractive for new generation of the cable television transmission and local communication systems.
Dissociation of I2 by O2(a1D), with subsequent excitation of I*, was first observed by Arnold et al.1 in 1966. This key discovery led to the eventual development of the chemical oxygen iodine laser (COIL). The mechanism by which I2 is dissociated was not determined by Arnold et al.1 and has remained elusive, despite many experimental attempts to unravel this question. Although the details are not known, it is apparent that a complex interplay between vibrationally and electronically excited states of I2 is involved. Vibrationally excited states of O2 have also been implicated. Characterization of the dissociation process is an important issue for COIL as the efficiency is impacted by the energy cost of dissociating the iodine. In this paper we provide a historical summary of work on the dissociation mechanism, and summarize the current understanding of the problem.
The dissociation of I2 by O2(a1Æ) is a critical process for the chemical oxygen iodine laser. Despite many years of study the dissociation mechanism is not properly understood. Currently accepted models assume that vibrationally excited I2 is the immediate precursor to atomic I. However, studies of I2 vibrational relaxation kinetics cast doubt on this assignment. New measurements of quenching rate constants for I2(A') indicate that electronically excited I2 is a more likely precursor. A revised kinetic model for the dissociation process is proposed, based on the active participation of electronically excited I2. Vibrationally excited I2 remains an important species in this model as the I2 must be vibrationally excited before the electronically excited states can be accessed. A preliminary rate constant package for the new model is presented.
Metastable NCl(a1(Delta) ) is a promising energy carrier for use in chemically driven iodine lasers. The present studies of NCl(a) kinetics and demonstration of a non- intrusive method for detecting NCl(X) were conducted in support of efforts to develop an NCl(a)/I laser system. Photolysis of ClN3 by O2, H2, HCl, Cl2 and ClN3 were determined. The result were consistent with recent measurements made in a discharge flow system. NCl(X) was detected via transient absorption of the b-(chi) system. A CW ring dye laser was used to record a high-resolution spectrum of the origin band. Time resolved absorption measurements were used to examine the kinetics of NCl(X) formation and decay.