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Deuterium Lamp Layout NEWEST Deuterium Lamps Cathodeon The Ultimate Source Cathodeon DEUTERIUM LAMPS CONTENTS 1 Introduction 2 Internal structure 4 Envelopes 5 Window materials 7 Lamps in operation 8 Selection criteria 14 Fibre-coupled deuterium lamp 15 Industrial deuterium lamps 16 VUV lamps 17 Analytical VUV lamps 18 Power supply for deuterium lamps 19 Pulsed deuterium lamps 20 Power supply for pulsed deuterium lamps 21 High power deuterium lamp 22 Power supply and housing for high power deuterium lamp 23 Modulated deuterium lamp system 24 Useful notes 1 Deuterium Lamps Cathodeon CATHODEON DEUTERIUM LAMPS INTERNAL CONSTRUCTION Cathodeon Ltd, with almost 60 years experience in vacuum/gas INTRODUCTION filled electronic devices, is the world leading specialist in Fig 2a Standard deuterium lamp spectral source technology. Involved in the design and Anode Compartment manufacture of deuterium lamps since the earliest days of Arc Aperture instrumental spectroscopy, the company was ideally placed to Anode meet the challenges imposed on deuterium lamp performance Box by the low noise and drift requirements of HPLC during its Dimple Structure rapid growth in the early 1970’s. This long experience and Filament Shield expertise in deuterium arc lamp manufacture has resulted Cathode in an unrivalled range of products to meet many scientific Front Aperture needs. Continuing improvement to production techniques, Cathode quality control standards and test specifications ensure Dimple / Centre Plate Compartment that Cathodeon deuterium lamps remain the first choice Compartment of instrument manufacturers and discerning scientists APPLICATIONS throughout the world. For users wishing to combine light from another source with Deuterium arc lamps are the beam from the deuterium lamp, a “see through” facility is Fig 1 Spectral distribution offered. With this type of lamp, a light beam typically from a broad band sources of tungsten halogen lamp can be projected through the deuterium ultraviolet light, filled with From uncalibrated spectrophotometer arc on the same beam axis. deuterium at carefully Fig 2b See through deuterium lamp controlled pressures. Auxilliary source They provide a continuous Relative Intensity Arc Aperture UV spectrum from 180nm 0 Anode 200 300 400 500 600 700 Box to 370nm. They are used Wavelength (nm) Dimple Structure most commercially availab Filament Shield Cathode spectrophotometers, Front Aperture liquid chromatography GENERAL CONSTRUCTION The basic deuterium lamp construction consists of a pinch detectors and various othe base or a pin base, onto which a box structure is built. The box structure, made of high purity nickel, contains specialised photometric the anode, the cathode, the arc aperture and forms the front aperture. The box itself acts as a shield and ensures equipment designed for us that the discharge only occurs between the anode and the in the ultraviolet waveband cathode, as well as preventing the less stable “cathode glow” radiation escaping from the lamp. Inside the box Applications include: structure in separate compartments are a triple oxide cathode, consisting of barium, strontium and calcium mixed oxide, and the anode which is usually a flat molybdenum plate. Spectrophotometers The internal electrode structure is such that it enables striking and sustains a confined arc discharge which strongly HPLC detectors emits ultraviolet light over a broad continuum. The shape of the arc aperture can be either a circle or a slot depending Capillary zone on optical requirements. The resulting narrow cone light output electrophoresis (CZE) enables easy focusing into instrument optics. Around the box assembly is a cylindrical envelope, usually of transparent Stack gas analysers natural fused silica or UV glass. The complete assembly is processed and finally filled with 99.7% pure deuterium gas Medcial instruments at a controlled low pressure. Deuterium is chosen as it produces a more intense UV continuum than hydrogen. Densitometers Colorimeters Pollution analysers 2 Deuterium Lamps Cathodeon THE BASE Stability is especially improved in late life when arc shift, INTERNAL Cathodeon deuterium lamps are built up on either a 3 pin a common failure mechanism, is delayed. pinch base or a 7 or 9 pin moulded base. The moulded Fig 4a 3V Filament Frame Assembly glass base is used exclusively with UV glass lamps and STRUCTURE provides excellent mechanical stability, especially useful in prealigned applications. Fig 3a 7 Pin Moulded Base CL CL CL CL Fig 4b 10V Filament Frame Assembly CL The pinch base uses molybdenum pins which provide the base for building the internal structure. Fig 3b 3 Pin Pinch Base CL FILAMENT SHIELD CL CL CL The filament shield is primarily intended to mask any extraneous cathode glow from the optical path. In addition, CL this component, which plays a role in the inherent strike voltage of a given lamp construction, may be used to control All bases are tested for leaks at an early stage of manufacture evaporated barium being transported around the lamp and using a helium leak test mass spectrometer. This helps to can be used to elongate the positive column of the discharge ensure the high levels of mechanical integrity necessary for to increase intensity. long life deuterium lamps. DIMPLE STRUCTURE THE ANODE The arc aperture can be made with varying sizes and the The anode is made of molybdenum, due to the high shape of the aperture can be either as a circle or as a slot, temperatures experienced by this component and is placed depending on optical requirements. near the centre of the envelope, completely shielded from other parts of the lamp by the box structure. The anode is Circular arc apertures are available with the following sizes:- either in the form of a plate or a rod. The plate anode can 0.5mm 0.75mm 1mm 2.5mm have a hole in its centre enabling close running voltage Slot arc apertures are available with the following sizes:- control. Without the hole, improved reflected brightness is 2.5 x 1mm 5 x 1mm obtained from the lamp, whilst strike voltages are generally lower. The other version of the anode is in the form of a rod, Lamps with slot arc apertures are unique to Cathodeon and which is used in slot arc aperture lamps. This type of anode when combined with a rod anode have the advantage of enables the lamp to fill the the entrance slit more evenly with light. being able to couple well to long monochromator entrance THE CATHODE slits, however the highest levels of stability are not attainable Cathodeon lamps use directly heated cathodes, as the with these lamps. For the more common circular arc apertures, theoretically improved performance of indirect cathodes has the smaller the diameter of the hole the brighter the lamp APPLICATIONS not been realised and does not outweigh the considerable will be. The 0.5mm diameter dimple is a very bright point cost disadvantage. The cathode consists of a complex tungsten source, used for high radiance HPLC and capillary zone The arc aperture can be spiral or filament coated with emissive material, usually a electrophoresis (CZE) applications. The 2.5mm diameter made in 0.5mm, 0.75mm, barium, strontium, calcium mixed oxide. The filament voltages arc apertures are use for AA background correction where a can range from 2 - 12V depending on lamp type and are comparatively large hollow cathode beam is to be matched 1mm, and 2.5mm sizes, switched on for at least 30 seconds before application of to the arc. Dimples can either be 0.5mm, 0.75mm or 1mm the striking voltage to heat the cathode. The emissive life standard depth or they can be made as deep/parabolic dimples. and the shape of the of a cathode can be seriously damaged if insufficient heat is A deep dimple provides a partially collimated beam and is attained before striking. After striking, the cathode is heated a good irradiant source for spectrophotometers and for aperture can be either by the discharge itself and the lamp may be run with the fluorescence. Due to the flat even illumination of the beam as a circle or as a slot heater voltage off, so reducing heat dissipation and enabling profile, these lamps illuminate the slits more fully within simpler power supplies to be used. Maximum stability can spectrophotometers and are particularly suitable for prealigned depending on optical be maintained by running the lamp with continuous heater applications. The 0.75mm lamps are particularly useful as voltage, so maintaining the emissive surface at sufficient they offer improved output whilst still fully filling optics requirements. temperature to sustain the arc without fluctuation. designed for older lower performance 1mm lamps. 3 Deuterium Lamps Cathodeon The size, shape, intensity and stability of the arc are Fig 6b Output vs Front Aperture considerably influenced by choice of dimple shape, materials, geometry and gas pressure for a given electrical dissipation. INTERNAL 6 x 4mm Cathodeon lamps can be tailored to suit specific customer beam profile requirements. STRUCTURE 4.5mm Fig 5 Ouput vs dimple shape ront Aperture F 200 3.0mm 150 0 20 40 60 80 100 Relative Output 100 SEE THROUGH DERIVATIVES 50 Relative Intensity at 200nm Relative For users wishing to combine light from another source with the beam from the deuterium lamp, a “see though” facility 0 is offered. This version of the deuterium lamp is only available 21012 in 1mm and 2.5mm arc apertures as smaller apertures will not Displacement (mm) Key allow sufficient light through the lamp. The rear aperture can Std 1mm Parabolic 1mm Std 0.5mm be chosen to suit the optical system. These “see through” lamps are often used in conjunction with tungsten halogen lamps. THE FRONT APERTURE Front Apertures Available: Circular: 3mm or 4.5mm diameter Rectangular: 5 x 0.8mm, 5 x 2mm, 6 x 4mm or 12 x 3mm The front aperture controls the passage of the UV continuum from the positive column to the instrument.
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