3-4-2009

Crack Test of the si substrate to be used in the low scatter table beam dump.

Attached are a few pdf’ and Jpg’s showing various setups

Beam Dump Construction

The beam dump will be constructed of a mirror polished Stainless sq. cone {16 deg.} this cone will be baked, and a layer of oxidation will occur on its surface to absorb the beam energy at the rate of ~80% for each of 9 bounces.  The first bounce off an si substrate itself absorbing approx 98 percent ( the major portion ) of the energy.

The mount feet will be a small path, stainless material limiting the conductive flow to the table. The dump assembly can be mounted in a vertical or horizontal configuration at 3” and 4” heights from the table.

This assembly has been setup with a 40 watt fire rod to test the convection flow, with the fins vertical and horizontal showing that no point on the assembly exceeded 100 F.

SI Substrate Durability Test

The test is to determine if  the substrate will crack due to temperature differential in the substrate

local to the beam incidence.

The si mirror was set at brewster's angle ~73.4 deg for maximum absorption of the laser energy.

Rana and I set up the si substrate by simply clamping it to a stage, and adjusting, and orienting it to center the 1064 laser  beam.

Initially the laser output was 8.6 watts, the si substrate did not crack, the temperature rose to a steady 105 F after

about one minute.

Next after Peter King adjusted the laser internally a retest was made at 32 watts, this also did not crack the substrate and after about one minute the substrate temp rose to a steady 206 F. given the beam is smaller in diameter  than the actual beam, Rana’s opinion was it ‘passed’ the test and we should proceed with the design.

The beam dump when assembled will have a finned aluminum heat sink in contact with the substrate.

An additional test will be made to determine compatibility of the si interface material, re. thermal expansion of the

aluminum heat sink / bonding material / si substrate, in the end we can just pot it, and use the cone to secure the si in a machined recess in the heat sink body.