A Guide to Helical Xenon Flash Tube


As an electric arc lamp, a helical xenon flash tube can produce extremely full-spectrum, incoherent, and intense white light for short times. Designers used electrodes on both ends with glass tubing to make the flash tube. When a user triggers it, it produces the light by ionizing and conducting a high voltage pulse. While the photographic platform gets the most use of the helical xenon flash tube, others who employ it are entertainment, industrial, medical, and scientific industries.


Bursting with a noble gas, there is a hermetically sealed glass tube in the lamp. This noble gas is typically xenon. Also essential to transmitting electrical current to the gas are the electrodes, and vital to boosting the gas for any trigger occasion is a high voltage power source. Operators also use a charged capacitor for the supply of energy to the flash. With that, when they trigger the lamp, they can have speedy delivery of high electrical current.

Glass Envelopes

The glass envelopes are made of Pyrex, borosilicate, or fused quartz and typically thin. These can be bent or straight into several different shapes, such as circular, U shape, and helical. Whether because of plastic degradation, laser rod damage, ozone production, or other detrimental impacts, some applications may not need the ultraviolet light emission. As such, users can use doped fused silica in these cases. With that, they can get different cutoff wavelengths on the ultraviolet side when doping with titanium dioxide. However, solarization may impact the material. This case is because they typically use it in non-laser lamps, sun-ray lamps, and medical lamps. Cerium-doped quartz tends to be a better alternative. Since the fluorescence reradiated part of the absorbed ultraviolet as visible, it has higher efficiency and does not suffer from solarization. Users can get their cutoff at around 380 nm. Conversely, they use synthetic quartz as the envelope when calling for ultraviolet. Though its cutoff is at 160 nm and susceptible to solarization, its materials are the most expensive.

The rate of the lamp’s power level is in area/watts, and the lamp’s inner wall surface divides the total electrical input power. Essentially, it is quite crucial to cool the lamp envelope and electrodes at high power levels. Lower average power levels can cause enough of the air cooling. Operators use a liquid to cool high power lamps with a tube they use to encase the lamp by flowing demineralized water. The glass will shrink around the electrodes due to water-cooled lamps to provide a direct thermal conductor between the cooling water and the electrodes. There must also be a cooling medium flow across the whole length of the electrodes and lamp. There must also be water flowing across the exposed electrode ends and the continuous-wave arc and high average power lamps. As such, operators can use deionized water to prevent a short circuit. There is a need for above 15 W/cm2 forced air cooling. They can use liquid cooling when in a compact space, and when it is above 30 W/cm2, liquid cooling is required.

Because the thinner walls have lower mechanical strain across the material thickness, they can survive loads with higher average-power. Between the cooling water and hot plasma, a temperature gradient caused the mechanical strain. Thus, operators use thinner glass when designing continuous-wave arc lamps. The belief is that with thicker material, it will be possible to handle the shock wave energy impact that can be generated by a short-pulsed arc. As such, they typically use quartz that is about 1 mm thick for flash tube construction. The output power has another limit from the envelope material. The limit for 200 W/cm2 is 1 mm thick fused quartz. However, there may be about 240 W/cm2 for synthetic quartz with similar thickness. Borosilicate and some other glasses don’t have the same power loading capacity as quartz. And because of the increased glass energy absorption resulting from sputtered deposits and solarization, there is a need for some derating for aging lamps.

Seals and Electrodes

People can use different techniques to seal each tube end as the electrodes protrude into them. They can bond ribbon seals with its thin molybdenum foil strips directly to the glass, and with that, they can have a durable project. However, they will have a limited amount of current passing through. If they are looking for a robust mechanical seal, they can use solder seals for the glass. However, this sealing can only be useful with the low-temperature operation. Rod seal is the most common with laser pumping applications. With this, the designer wet the electrode rod using a different glass type. They will then bind it to a quartz tube directly. They can have a durable seal capable of outweighing high currents and temperature. The glass and the seal need to have a similar expansion coefficient.

Users can have low electrode wear with tungsten electrodes. It has the highest melting point for metals and can handle the electrons’ thermionic emission. The byproduct of porous tungsten are cathodes with a barium compound fill. People can get low work functions with it. Therefore, they must tailor the cathode structure for the application. Anodes are made from pure tungsten. They are also made when there is a requirement for good machinability. People machine them to offer additional surface space to handle the power loading.

There is mostly a sharp-tipped cathode with DC arc lamps to control temperature and keep the arc away from the glass. And to decrease sputter peak currents may cause and reduce the hot spot event, there is a flattened radius cathode with flash tubes. What also influences electrode design is the average power. Operators must take note to achieve enough electrode cooling when at high levels of average power. The lamp’s life expectancy may significantly reduce through cathode overheating, even when there is lower importance for anode temperature. Regarding the fill pressure and gases, people may have a range of a few kilopascals to hundreds of kilopascals of gas fill pressure, depending on the flash tube application, type, and size. They will have a greater output efficiency with a higher pressure.


Latest Issue

BDC 318 : Jul 2024