Optical characterisation of hydroxide catalysed bonds applied to phosphate glass

We apply the Hydroxide Catalysis Bonding (HCB) technique to phosphate glass and measure the reflectivity and
Light Induced Damage Threshold (LITD) of the newly formed interface. HCB is a room temperature, high performing
process which was designed for astronomical research glass assemblies and played a key role in the detection of
gravitational waves, a breakthrough in contemporary science. The bonds have numerous assets including mechanical
strength, stability, no outgassing and resistance to contamination which are of high interest in the precision optics
industry. However only little research has been done on their optical properties and mostly on silica based materials. In
this paper, we use HCB to bond phosphate glass at room temperature with the goal of designing composite components
for solid state laser gain media. We change the solution parameters to identify how they influence the final properties of
the bonds: the LIDT at 1535 nm in long pulse regime and the reflectivity at 532 nm are investigated. The measurement
of the incidence dependent reflectance allows estimating the thickness and refractive index of the bond in a non
destructive process. The best performing set of parameters yields a LIDT of 1.6 GW/cm2 (16 J/cm2) and a reflectivity
below 0.03 % which makes it suitable for use in high power lasers. The bond thickness is derived both from Scanning
Electron Microscopy and the reflectivity measurements and is in the range of 50-150 nm depending on the parameters.
Finally, the bonds survive cutting and polishing which is promising for manufacturing purpose.