Automated precision alignment of optical components for hydroxide catalysis bonding

Abstract

We describe an interferometric system that can measure the alignment and separation of a polished face of a transparent optical component and an adjacent polished surface. Accuracies achieved are ∼ 1µrad for the relative angles in two orthogonal directions and ∼ 30µm in separation. We describe the use of this readout system to automate the process of hydroxide catalysis bonding of a fused-silica component to a fused-silica baseplate. The complete alignment and bonding sequence was typically achieved in a timescale of a few minutes, followed by an initial cure of 10 minutes. A series of bonds were performed using two fluids-a simple sodium hydroxide solution and a sodium hydroxide solution with some sodium silicate solution added. In each case we achieved final bonded component angular alignment within 10 µrad and position in the critical direction within 4 µm of the planned targets. The small movements of the component during the initial bonding and curing phases were monitored. The bonds made using the sodium silicate mixture achieved their final bonded alignment over a period of ∼ 15 hours. Bonds using the simple sodium hydroxide solution achieved their final alignment in a much shorter time of a few minutes. The automated system promises to speed the manufacture of precision-aligned assemblies using hydroxide catalysis bonding by more than an order of magnitude over the more manual approach used to build the optical interferometer at the heart of the recent ESA LISA Pathfinder technology demonstrator mission. This novel approach will be key to the time-efficient and low-risk manufacture of the complex optical systems needed for the forthcoming ESA spaceborne gravitational waves observatory mission, provisionally named LISA.

An automated system for hydroxide catalysis bonding of precision-aligned optical systems

“…In all cases the reflecting optical surface is within 4µm of its nominal position and the angular errors are below 10µradians. Full details of the bonding timeline and the fluids used are given in 7 .…”

“…Our system of aligning and bonding is described in detail in a separate papers 7,8 , but it is useful to summarise briefly the alignment requirements and technologies used. Figure 1 shows a component to be bonded and the axes used to describe its location.…”

The LISA optical bench: an overview and engineering challenges

“…This follows the same design principle as the LISA pathfinder optical bench 5 . Following on from pathfinder, the LISA optical bench will also be assembled using Hydroxide Catalysis (HC) bonding 6,7 . See [5 and 8] for details on the metrology techniques used to assemble LISA and LISA pathfinder optics to high accuracy.…”

“…But given that the imaging system optics need to be kept very stable (so as to avoid introducing TTL) the reflective design is preferred. This is because reflective optics can be easily mounted to the optical bench using HC bonding, which is the technique used for mounting other optics to the optical bench 6,7 . Optics that are HC bonded to the optical bench are made from Silica, which closely matches the CTE of the Zerodur optical bench baseplate, making the optics very thermally stable.…”

The First Round Result from the TianQin-1 Satellite

“…The study of ultra-stable laser interferomter for space-based GW mission started since the last decades of the twentieth century [15,16,17,18]. LISA Pathfinder uses an ultra-precision laser interferometer equiped with a quasi-monolithic optical bench to detect the relative motion between the two TMs onboard the spacecraft.…”