Chemical Oxygen Iodine Laser Technologies Laboratory Complex Demonstrator
Intensive investigations of COIL technologies, which were held in Russia, the USA, China, Japan, Germany, Israel and other countries, reached a high level of development since the first laboratory demonstration of the laser in the US on 1977 [1–4]. The highest point was the implementation of the program ABL (Airborne Laser, USA) , under which the megawatt-class chemical oxygen-based-iodine laser system installed on the plane was successfully tested for destroying of ballistic missiles at ranges of up to 400 km.
An example of the solution of such complex task may be considered the COIL laboratory and demonstration complex developed by scientists and engineers of "Laser Systems’ Ltd., Ustinov Baltic State Technical University "VOENMEH" and Samara Branch of the Physical Institute of Russian Academy of Sciences. The laser system was successfully brought into operation at the test-site of the customer in the National Chung-Shan Institute of Science and Technology (Taiwan).
This complex includes the CW (duration of one start-up to 30 seconds) chemical oxygen iodine laser with the nominal power of 200W (laser module), the component storage and supply system, dual-mode exhaust system (vacuum system), data acquisition and control system, as well as fiber – optical transfer system. The scheme of the complex is presented in Fig. 1, while the main technical characteristics of the equipment are included in Table 1.
Component storage and supply system
Component storage and supply system (Fig. 2) includes follow main parts: BHP preparation and supply system, chlorine storage and supply system, iodine storage and supply system and nitrogen storage and supply system.
Singlet oxygen generator
One of the key element of COIL – SOG is designed to produce electronically excited oxygen is able to О2 (1∆) (singlet oxygen) in the gas-liquid reaction of chlorine gas with BHP.
Centrifugal bubbling SOG (Fig. 3) was used for laboratory complex. In SOG the liquid BHP fed to an inner surface of a rotating cylinder. Chlorine gas is blown through cylindrical nozzle which are submerged in the solution. As a result, bubbles are formed under the influence of centrifugal acceleration move in the radial direction and make gaseous О2 (1∆).
Centrifugal bubbling SOG provides the low ratio of solution flow rate to the chlorine flow rate up to 1 liter/mole , which is important for mobile systems. In addition, centrifugal bubbling SOG provides high chlorine utilization (at least 90%) and singlet oxygen yield (60%).
Laser module (Fig.4) includes the nozzle bank, laser cavity with optical resonator and supersonic diffuser.
The nozzle unit is a single laser shaped slit nozzle for producing a supersonic flow in the laser cavity, and iodine injector. The primary stream containing the singlet oxygen is supplied from SOG in the nozzle pre-chamber. The secondary flow, containing molecular iodine, is supplied to the transonic region perpendicular to the primary flow.
The laser cavity is formed with extension sections to offset the heat generated in the flow, as a result of chemical reactions. At the walls of the cavity boxes are installed the adjustment mounts for resonator mirrors.
The optical resonator and its design provide the laser radiation with desired spatial, temporal and spectral parameters. Stable type resonator is used, it is less sensitive to misalignments and allows the best use of the volume of the active medium. In this embodiment, a resonator is multimode with intracavity aperture. Output mirrors and resonator scheme are shown in Fig.5.
Intracavity diaphragm provides filtering transverse modes for the efficient removal of power at the center of the active medium and forms a circular profile of the output radiation for subsequent input into the fiber.
The fiber is used for the transport of laser beam at a distance of 80 meters. Transport fiber is a quartz fiber with a core diameter of 800 microns, placed in a protective casing and having two connectors, input – SC-01, water-cooled and an output – a standard SMA-905. Coupling beam into the fiber was carried out using a specially developed and produced VOLO Ltd. input unit (Fig.6). Power input radiation was about 250 watts. The design of the module allows an alignment the axis of the output laser radiation and fiber with high accuracy, providing optimum input radiation.
Active medium exhaust system
Various technologies can be used for exhaust of COIL active medium in the environment and providing a low operating pressure in the laser cavity  – vacuum tanks, mechanical vacuum pumps, ejector type pressure recovery system (PRS), and cryosorption pump.
The utilization of COIL active medium is the most relevant issue, since the efficiency of the pumping system greatly affects the weight and size characteristics of the laser system. COIL mobile systems may be based on use only the PRS or cryosorption pumps.
The active medium exhaust system of the laboratory complex uses dual-mode approach (Fig.7). The laser can operate with both mechanical and the cryosorption pump.
Mechanical system consists of two series-connected vacuum pumps and provide operation of installation for an unlimited period of operation. This system is regarded as the main work of the laboratory complex.
Cryosorption pump is a vacuum container with internal cryopanels, which is filled with adsorbent (zeolite or activated charcoal) cooled by liquid nitrogen. However the special cryogenic trap has to be installed between the laser and cryopump. It is necessary to clean the active medium moving off residual chlorine and iodine, decreasing sharply of the sorption capacity.
The cryosorption pump allows the laser to operate for a limited time, determined sorption capacity, so it is not the main intended for research and cryogenic pumps themselves in a work with a real laser.
Data Acquisition and Control System
Data acquisition and control system (DACS) presents a specialized complex of hardware and original software. It is intended for automated control of executive devices, for control of subsystems state during all exploitation stages and also for data acquisition from sensors, data processing and storage in database of results. DACS provides the operation of 28 control channels, 37 measurement channels and 7 automated tasks with sampling frequency 30 Hz.
Maximum performance problems have been associated with extremely short delivery times and delivery of the laser to the Customer, and the production and assembly of the equipment occurred in the last quarter of 2014. Despite this, assembly and commissioning of the laboratory and demonstration plant at the stand of the Customer completed timely (Fig.8), and by mid-May 2015 the complex was completed through the acceptance tests.
During the tests was made on the project level of output power and duration of laser generation in the various modes of laser operation, the cryosorption pump capacity was confirmed, and the high-power laser radiation was transmitted through the fiber with 80% efficiency.
Moreover, as shown initial work experience, laboratory equipment of demonstration complex gives the opportunity to explore all the main COIL technology, varying over a wide range characteristics of the installation: the flow rates of the components, the parameters of the SOG, the geometric dimensions of the nozzle bank, the type of cryopump adsorbent and others. Modular design allows the flexibility to change the configuration of the complex without a serious alteration of the installation due to replacement of the main elements of the laser – use other types of SOG, as well as apply different schemes of mixing primary and secondary flows.
In general, to our delight and customer satisfaction all the work on installation of the equipment, start-up and COIL demonstration laboratory complex and the achievement of all the design parameters was performed accurately in time and with high quality assessment work.
The authors express their sincere gratitude to all colleagues who participated in the development, manufacturing and testing laboratory complex:, K.O.Alexeyev, A.A.Myasnikov, M.S.Antonov, A.O.Trukhin, N.N.Gavryutin, S.E.Avferonok, M.I.Svistun and other our colleagues of Laser Systems Ltd., BSTU "VOENMEH", and Samara branch of Lebedev Physical Institute.