8 - Optical Diagnostics of Singlet Oxygen for Chemical Oxygen–Iodine Laser

Summary

Introduction

Chemical oxygen−iodine laser (COIL) was first demonstrated by McDermott et al. in 1978 and is the only chemical laser based on electronic transition. It operates on ²P_1/2 → ²P_3/2 transition of iodine atom at 1.315 μm and is pumped by the following reaction scheme,

This laser due to its short wavelength, high efficiency and scalability has found application in various military and civilian scenarios in the last decade. The possibility of carrying high power beams via optical fibers makes it extremely useful for decommissioning and dismantling dangerous structures such as obsolete nuclear reactors through remotely operated mechanisms by Tei et al.

The pumping source, O₂(¹) is an excited form of oxygen molecule with energy level very close to that of atomic iodine enabling near resonant energy transfer as shown in Fig. 8.1. Although, different techniques such as chemical, RF discharge, photo-sensitizer, have been reported for the production of O₂(¹), the chemical method is the only one till date that has been successful for scaling up power. Therefore, amongst the variousmechanisms studied for the production of O₂(¹), the chemical method still remains at the forefront for the development of large-scale COIL systems. The chemical method is based on chemical reactions between chlorine gas and basic hydrogen per-oxide (BHP) solution resulting in production of singlet oxygen, which in turn dissociates iodine molecules into iodine atoms and also subsequently excites these atoms.

For an efficient production of singlet oxygen, jet type singlet oxygen generator (JSOG) by Rajesh et al. has proved its potential over the other techniques such as rotating disc or bubbler type. Other forthcoming generators such as twisted aerosol and centrifugal bubble/ flow type are yet to be proven for large-scale power levels.

Figure 8.2 shows the functional block diagram of chemical oxygen iodine laser[3, 9] which exhibits coupling of all subsystems. BHP solution is prepared in a separate preparation tank and supplied to the SOG reaction chamber in the form of jets. Chlorine is supplied to the SOG reaction chamber from the bottom in a counter-flow direction to the jets so that it reacts at the surface of the liquid jets to produce singlet oxygen molecules.