GB2392719A

GB2392719A - Cooling jacket for a flashlamp

Info

Publication number: GB2392719A
Application number: GB0220424A
Authority: GB
Inventors: Antony David Case
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2002-09-03
Filing date: 2002-09-03
Publication date: 2004-03-10
Also published as: GB0220424D0; AU2003255830A1; WO2004023613A1

Abstract

A cooling jacket for a flashlamp or arc lamp has an outer surface roughened by an etching agent, sandblasting or manual abrasion. This reduces the fraction of radiation generated by a lamp having a cooling jacket and undergoing total internal reflection at the surface, thus increasing the useful optical output power of the lamp. A flashlamp- or arc-lamp pumped laser having a lamp with such a cooling jacket shows improved overall electrical-to-optical conversion efficiency and higher output energy for a given pump energy.

Description

23927 1 9

COOLING JACKET FOR A FLASHLAMP OR ARC LAMP

The invention relates to cooling jackets for flashlamps and arc lamps, to flashlamps and arc lamps per se, and to lasers pumped by flashlamps and arc 5 lamps which have cooling jackets. The invention also relates to methods of fabricating cooling jackets.

Flashlamps, arc lamps and similar lamps are used, inter alla, for pumping lasers.

Various optical sources have been employed in the past to pump lasers, however 10 today only flashlamps, arc lamps and laser-diodes are of practical interest.

Although laser-diodes have the benefits of robustness, electrical efficiency, longevity and good spectral overlap with ions typically used in solid-state lasers (e.g. ions of rare-earth elements), flashlamps and arc lamps remain useful, particularly in high output power lasers.

A flashlamp is an elongate device comprising a linear or helical quartz tube filled with an inert gas (e.g. xenon or krypton at a pressure of 200 - 700 tort at room temperature) and designed such that, in operation, a plasma fills most of the tube. Electrodes are commonly sealed into the body of the flashlamp by one of 20 two techniques. In the first technique, a tungsten electrode is sealed to the quartz tube with highly-doped borsilica glass. A copper rod is used in the second technique; one end of the rod is brazed to an electrode and the other is welded to a copperplated nickel cup. Indium solder is used to seal the cup to an end of the quartz tube. Arc lamps are of similar construction.

In the case of a flashlamp or arc lamp with a high average optical output power, cooling of the quartz tube and electrode-seal areas is provided either by a gaseous coolant such as forced air or pressurised nitrogen, or by a liquid coolant such as water, a water-alcohol mixture or a CFC. The coolant is circulated in an outer 5 cooling jacket of the flashlamp or arc lamp. In many designs, the outer cooling jacket is reusable after the lamp itself has reached the end of it useful life. In other designs the cooling jacket is inextricably comprised in the lamp.

A problem with flashlamps and arc lamps having cooling jackets is that a 10 significant fraction of radiation produced by the lamp undergoes total internal reflection at the outer surface of the cooling jacket and is thus trapped rather than made available for use. For example, in a flashlampor arc lamp-pumped laser, trapped radiation is not delivered to the laser's gain medium. Up to 40% of the radiation generated by a flashlamp or arc lamp may be lost by this mechanism. In 15 addition to reducing overall efficiency, such loss results in less effective cooling of the lamp. In the case of flashlamp- and arc lamp-pumped lasers, overall electrical-to-optical conversion efficiency is limited by this effect.

An object of the present invention is to mitigate these problems.

According to a first aspect of the present invention, this object is achieved by a cooling jacket for a flashlamp or arc lamp characterized in that an outer surface of the jacket has a roughness sufficient to substantially reduce total internal reflection of radiation at said surface.

The roughened surface reduces total internal reflection so that only 15 to 20% of the radiation generated by a flashlamp or arc lamp within the jacket remains trapped therein, thus increasing the optical output power available for use.

5 A second aspect of the invention provides a method of fabricating a cooling jacket of the invention, the method comprising the step of applying an etching agent to the outer surface of a cooling jacket. Conveniently, etching may be carried out using an etching creme comprising ammonium bifluoride or hydrofluoric acid.

Alternatively, sandblasting or manual abrasion may be employed. Sand paper or 10 glass paper may be used to effect manual abrasion.

A flashlamp or arc lamp comprising an outer cooling jacket according to the first aspect of the invention is provided by third aspect of the invention. Such a lamp has an improved electrical-to-optical conversion efficiency compared to a 15 flashlamp or arc lamp of the prior art. A fourth aspect of the invention provides a

flashlamp- or arc lamp-pumped laser comprising a flashlamp or arc lamp according to the third aspect of the invention. Such a laser has a higher output energy and a higher electrical-to-optical conversion efficiency than prior art

flashlamp- or arc lamp-pumped lasers.

Although cooling jackets typically envelop the whole of the quartz tube of a flashlamp or arc lamp, the invention may also be applied to a cooling jacket which only partially surrounds a flashlamp or arc lamp.

25 Embodiments of the invention are described below by way of example only.

The invention may be put into practice by etching the outer surface of a quartz cooling jacket of a flashlamp with ammonium bifluoride-based etching creme, for example Etchall@, as follows. Open ends of the jacket are stoppered using fluoride-resistant stoppers (e.g. SubasealR' stoppers) to prevent etching of the 5 inner surface of the jacket. A plastic measuring cylinder is filled with etching creme and the jacket completely immersed therein for 24 hours (although the exact time is not critical). A cover plate is placed on top of the cylinder to ensure that the jacket remains fully immersed in the etching creme.

10 Etching may also be carried out using hydrofluoric acid (HE) or HFbased products such as HE paste, by sandblasting or by manual abrasion. Sand-paper or glass-

paper is useful in the latter case.

The cooling tubes of the flashlamps of a Cocoa-Tinn Mark II flashlamppumped 15 dye laser were etched with Etchall in order to obtain increased output power from the laser. Measurements of pulse energy were made before and after etching, the arrangement of the laser otherwise being the same in both cases.

The mean pulse energy of optical pulses output from the laser before etching was 2.21]. After etching, the mean pulse energy was 2.90], corresponding to an 20 increase in mean pulse energy due to etching of 31%. A one-sided two-sample t-

test resulted in a specific probability value less than 0.001, giving overwhelming evidence that that energy of the pulses was increased.

Claims

1. A cooling jacket for a flashlamp or arc lamp characterized in that an outer surface of the jacket has a roughness sufficient to substantially reduce total 5 internal reflection of radiation at said surface.

2. A flashlamp or arc lamp comprising a cooling jacket according to claim 1.

3. A laser comprising a flashlamp or an arc lamp according to claim 2.

4. A method of fabricating the cooling jacket of claim 1, the method comprising the step of applying an etching agent to the outer surface of a cooling jacket.

5. The method of claim 4 wherein the etching agent comprises ammonium 15 bifluoride.

6. The method of claim 4 wherein the etching agent comprises hydrofluoric acid.

7. A method of fabricating the cooling jacket of claim 1 comprising the step of 20 roughening the outer surface of a cooling jacket by sandblasting.

8. A method of fabricating the cooling jacket of claim comprising the step of roughening the outer surface of a cooling jacket by manual abrasion.

9. The method of claim 9 wherein the manual abrasion is carried out using glass paper.

10. The method of claim 9 wherein the manual abrasion is carried out using sand 5 paper.