Europe: Saxon Way, Bar Hill, Cambridge, CB3 8SL Tel: +44 (0)1954 782266 Fax: +44 (0)1954 782993 USA: 44370 Christy St., Freemont, CA 94538, USA Tel: (800) 775-OPTO Tel: (510) 979-6500 Fax: (510) 687-1344 USA: 35 Congress Street, Salem, MA 01970, USA Tel: (978) 745-3200 Fax: (978) 745-0894 Asia: 47 Ayer Rajah Cresent, 06-12, Singapore 139947 Tel: +65-775-2022 Fax: +65-775-1008 Japan: 18F, Parale Mitsui Building 8, Higashida-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, 210-0005 Japan Tel: 81 44 200 9150 Fax: 81 44 200 9160 www.perkinelmer.com/opto Optoelectronics Lighting Imaging Telecom High Performance Flash and Arc Lamps Lighting Imaging Teleco m Introduction This publication is divided into two sections: Past, Present and Future Part 1 – Technical Information Solid state laser systems have historically used pulsed and CW (DC) xenon or krypton filled arc lamps as exci- Part 2 – Product Range tation for pump sources. When in 1960, at Hughes Research Labs, the first practical pulsed laser system Part 1 is intended to give the necessary technical infor- was demonstrated by mation to manufacturers, designers and researchers to T. H. Maiman the technology and understanding enable them to select the correct flashlamp for their involved in the manufacture and operation of application and also to give an insight into the design flashlamps was of a very basic nature. Up to procedures necessary for correct flashlamp operation. that time (1960) the major use of flashlamps was pho- Part 2 is a guide to the wide, varied and complex range tography and related applications. In fact the Maiman of lamps manufactured by ruby laser was pumped by a small, hard glass helical PerkinElmer Optoelectronics. It lamp, made by General Electric, intended for studio illustrates most of the photography. standard lamp outlines Throughout the 1960’s lamp and laser development currently in world-wide use for progressed hand in hand until by the later 1960’s lamp laser pumping and similar technology was fairly mature. During this applications, for example air period the quartz/tungsten rod seal flashlamp cooled lamps, fluid cooled had been developed, perfected and extensively adopt- lamps, high pressure krypton ed for high average power laser pumping. Also, during arc lamps, etc. this time, specialist laser lamp It would be difficult, if not manufacturing companies had been set up adding to impossible, to present all the the development and advancement of high possible design variations that technology laser lamps. can be produced. Lamp production has now progressed to the point This section therefore is a where many advanced high performance designs are guide and overview of routinely available off the shelf or can be PerkinElmer’s flash and arc lamp manufacturing pro- built in small quantities at short notice. Although pro- gramme. duction runs can be for several thousand lamps, they are still universally assembled using basically hand crafting techniques. It is because of this hand crafting that small production runs of specialised devices can be undertaken economically. Much work has been undertaken in recent years to further improve lamp technology in new, demanding applications. A great deal of lamp development work is concentrated at the cathode, where new, rigorous ser- vice conditions are encountered when lamps are operated at high average powers and pulse durations in the millisecond regime. PerkinElmer utilises it’s company-wide diagnostic techniques to aid this research. Techniques such as finite element analy- sis and x-ray analysis are tools that play a significant role in lamp development. PerkinElmer is more than a lamp manufacturer – it actively participates in the advancement of flashlamp technology through its connections with research establishments throughout the world, both at university and commercial levels. 2 Lamp Construction and Material Selection ENVELOPE MATERIALS in a wide range of sizes. The UV cut off Part 1Information – Technical commences at approximately 220 nm. The only major The term ‘envelope’ is universally used to describe the disadvantage of clear fused quartz is the problem of body or jacket surrounding the electrodes solarisation. This is the appearance necessary to contain the filling gas. The chosen enve- of a purplish discolouration due to colour centres form- lope material has to be transparent and able ing within the quartz. The colour centres are localities to transmit the useful light or radiation produced of ion impurities. These are thought to include ion, alu- by the lamp. It must also be impervious to air and the minium, germanium and some rare earths. Solarisation filling gas, withstand high temperatures and be results in a broad band reduction in the transmittance of mechanically strong. The material universally used for the quartz. The colour sites envelopes in the construction of flashlamps generally form during the and arc lamps for laser pumping is transparent fused high energy operation of quartz. It meets all, or most of the stated requirements, flashlamps. It does not is easily worked and is available appear to occur under in a wide range of sizes. low power conditions. Hard glass or pyrex is used extensively for Many flashlamp pumped lamps operating under conditions of low average laser systems use lamps power. This includes signal beacons, low power strobo- made from clear fused scopes and low power photographic quartz. It is not generally applications, i.e. camera flash guns. Under the possible to predict whether high power conditions required for laser pumping, glass a particular mode of operation will make a lamp simply cannot withstand the high thermal loading. more susceptible to solarisation. If problems are experi- Stress cracks will rapidly develop within the tubing enced with solarisation there are alternative types of leading to lamp failure. Quartz however is highly toler- quartz available to alleviate the problem. ant to thermal shocks. At red heat it can be plunged into cold water without damage and has a high soften- Doped Quartz ° ing point (1300 C). Pyrex The UV transmission properties of quartz can be modi- ° softens at approximately 600 C. fied by the incorporation of a dopant in the material. There is frequent confusion surrounding the This dopant usually takes the form of terminology used in quartz based products. Although cerium, or titanium oxides. The quartz still appears the term quartz is frequently used, its usage is some- clear but as Figure A shows, the UV transmission has what incorrect as it describes the basic mined, unre- been modified. This modification is desirable when fined ore, not the final product. The correct term is potentially damaging UV from the flashlamp must be clear fused silica. It is also referred to as vitreous silica, eliminated. This includes, in the case of a lamp operat- quartz glass, fused glass or silica quartz. The term ing in free air, the elimination of ozone or the preven- quartz, although incorrect, has become synonymous tion of UV damage to Nd:YAG rods, reflectors, plastics with and ‘O’ rings. flashlamps and for ease of reference will be Cerium Doped Quartz Clear fused quartz doped with used in this booklet. cerium oxide is finding increasing applications in flash- There are three major groups of quartz used in flash- lamps for laser pumping. The UV cut off lamp construction, clear fused quartz, doped quartz at approximately 380 nm ensures that harmful and synthetic quartz. Although all of UV is eliminated from the pump chamber. The UV them have similar physical properties as regards tem- absorption is accompanied by fluorescence in the visi- perature and strength they differ in their ble spectrum. As some of this falls in the absorption respective transmittance at the UV end of the bands of Nd:YAG an increase in laser efficiency can be spectrum, from 200 to 400 nm. expected. Significantly as cerium doped silica does not solarise it has very stable Quartz Types characteristics throughout lamp life making it a very desirable envelope material for flashlamps when Clear Fused Quartz laser pumping. This material is the basic building block for the majority of flashlamps. It has an upper operational limit of approximately 600°C and is readily available 3 Part 1Information – Technical Titanium Doped Quartz Clear fused quartz doped with thermal gradients can be formed in the quartz during titanium oxide is available in many different grades, lamp operation, possibly leading to the formation of each one having a different UV cut off stress cracks. Under conditions profile. It has similar characteristics to cerium doped of high average power and low peak power, e.g. kryp- quartz but suffers badly from solarisation and does not ton arc lamps, 0.5 mm wall thickness quartz have the fluorescence characteristic. Once used exten- is specified for maximum heat transfer from the lamp sively when UV filtering was required for flashlamps, it and to minimise the thermal gradient. has all but been The internal diameter of quartz tubing is normally avail- superseded by a cerium doped quartz. It is however able in whole mm increments. Intermediate sizes can frequently encountered in medical and sun ray be obtained if required. A general purpose tolerance for type lamps and non laser flashlamps when ozone must flashlamp tubing is ± 0.3 mm for the outside and inside be prevented. diameters. For small lamps of 2 to 4 mm bore and up to 75 mm arc, precision Synthetic Quartz bore tubing is available, giving good repeatability of In addition to doped and undoped quartz tubing there is lamp performance, especially lamp impedance. another type of quartz material available. This is high Generally the tolerance of quartz tubing becomes purity, man-made, synthetic quartz. It is widely speci- greater as the sizes increase. fied when transmission down to 160 nm is required.