LIGO Document T1800001-v2

IR beam dumps – evaluation of different materials: Black glass, sintered SiC, Si, DLC coated supe#8 SSTL

Document #:
LIGO-T1800001-v2
Document type:
T - Technical notes
Other Versions:
Abstract:
In this document I am presenting just some fun visualization of IR scatter from beam dumps constructed out of Black glass (same as D1600115 currently used in HAM6), sintered SIC and DLC coated super#8 SSTL

Optioned to replace black glass with some other material are being considered due to it`s low laser induced damage threshold, see E17000388

However black glass has an excellent optical performance particularly at Brewster`s angle – low reflectivity and very low scatter (see T1700128). But a the same time high absorption of coarse is guilty in warming up black glass beam dumps that cases holes and cracks in the beam dumps. SiC is known to sustain very high temperature. CVD type of SiC can be polished as glass but it is expensive (about $700 for two 2” by 3” plates fora v-shaped beam dump). Sintered SiC is inexpensive but very porous. It can`t be polished therefor it scatters. Additionally, SiC is more reflective than black glass. It can be AR coated but this would even increase the cost. Exact numbers for BRDF back scatter and reflectivity are posted here T1700128.

Polished silicon so far is the best candidate for high power areas.

DLC coated stainless steel would be preferred at lower power areas (4 W/mm^2) due to lower reflectivity particularly in case of small incident angles

Notes and Changes:
v2 - summary on laser damage, scatter, reflectivity and availability
v1 - some visualization of the scatter

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