Multifunction laser power meter
A laser power meter incorporating an absorber disc with a peripheral thermopile ring, either continuous or segmented, and an additional temperature detection element in the central portion, that enables measurement of beam size. This detection element can be a thermopile element, generally a ring of smaller diameter than the peripheral thermopile used, and located closer to the center of the absorber disc. With this arrangement the beam size can be measured, in addition to measurements of the power and the position of the beam. Alternatively, this centralized detection element can be a single thermocouple junction located at the center of the disc, which acts as the hot junction of a thermocouple pair. The second or cold junction is effectively located on the disc close to the peripheral thermopile. Alternatively, two temperature measuring elements can be used, one at the disc center and one at the periphery.
1. A disc for measuring properties of an incident optical beam, said disc comprising:
a central region for absorbing said optical beam;
a thermopile located radially outwards from said central region;
a single temperature measurement element disposed on the center of the surface of said disc within the confines of said thermopile; and
electrical contacts to said thermopile and to said temperature measurement element which enable measurement of the voltages generated by them, the ratio of the voltages measured on said thermopile and said temperature measurement element enabling the size of said optical beam incident on said disc to be determined,
wherein said single temperature measurement element is adapted to accurately measure the size of an incident optical beam having an area as small as the area of said single temperature measurement element.
2. A disc according to claim 1 wherein said temperature measurement element is a thermistor.
3. A disc according to claim 1 , further comprising an additional temperature measurement element at the periphery of said disc, such that said temperature measured on said temperature measurement element can be normalized according to the temperature measured at the periphery of said disc.
4. A disc according to claim 1 wherein said single temperature measurement element is a thermocouple having a single junction located at the center of the disc.
5. A disc according to claim 4 wherein the thermocouple is disposed such that electrical connection thereto is effected at the peripheral area of the disc.
6. A disc according to claim 1 , wherein said thermopile is divided electrically into separate segments, such that the position of impingement of said incident optical beam can be determined from the comparative voltages generated by said separate segments.
7. A disc according to claim 1 , wherein said thermopile has an effective diameter such that at least the majority of said central region for absorbing said optical beam is contained within said effective diameter.
8. A method for measuring properties of an incident optical beam, comprising:
providing an absorber disc for said beam, said disc having a central region for absorbing said optical beam, and a cooled periphery;
measuring a first voltage generated in a thermopile disposed on said disc radially outwards from said central region, said voltage resulting from impingement of said incident beam;
measuring a second voltage generated in a single temperature measurement element disposed on the center of the surface of said disc within the confines of said first thermopile; and
using the ratio of said first and second voltages to determine the size of said optical beam incident on said disc,
wherein the use of a single temperature measurement element enables accurate measurement of the size of an incident optical beam having an area as small as the area of said single temperature measurement element.
9. A method according to claim 8 wherein said single temperature measurement element is a thermistor.
10. A method according to claim 8 wherein said single temperature measurement element is a thermocouple having a single junction located at the center of the disc.
11. A method according to claim 8 , wherein said thermopile has an effective diameter such that at least the majority of said central region for absorbing said optical beam is contained within said effective diameter.