Development and operation of laser machined microwell detectors

Arrays of 100 mu m diameter cylindrical wells were laser micromachined on a 200 micrometer Cartesian grid, producing MicroWell Detectors (MWD). The su bstrate was 125 mu m thick polyimide foil, more than twice as thick as a ty pical GEM or WELL detector. An advantage of the laser micromachining proces s is that the wells are produced with nearly vertical sidewalls, in contras t to the sloping sidewalls characteristic of conventional chemical etching processes. With the steeper sidewall, active elements may be more closely p acked than is possible with wet etching techniques. Thicker substrates can be patterned, increasing the length of the charge multiplication region and reducing the internal capacitance per unit element. A series of prototypes have been produced and tested in a counting gas composed of 85% argon and 15% carbon dioxide, with a maximum measured gas gain of approximately 12 00 0. (C) 1999 Elsevier Science B.V. All rights reserved.