New High Temperature Acousto-optic Devices

Late last year, G&H (UK) Acousto-Optic Product Manager Rob Swain received a request from a global equipment and service provider for us to build an AO device capable of use in high temperature environments. The request was for a small near-infrared Acousto-Optic device operating at a minimum of 175°C, with the challenge of avoiding cracking resulting from differential thermal expansion. With the customer on a very fast track to prove the application this was an excellent opportunity for G&H to demonstrate our capabilities to take a new product from conception, through design, build, test phases to meet the rigorous demands for a new application and market, all in a short space of time.

Rob organized a collaborative design project that tapped into all of G&H’s AO design and manufacturing experience. While much of the collaboration was between our Ilminster and Palo Alto facilities, we also drew on experience from the Orlando, Cleveland and Melbourne sites. We set up a weekly conference call and together ranked potential solutions by degree of difficulty and chance of success. Designs for the most promising solutions were assigned to different members of the team to pursue. Choices were soon narrowed down to four variations that had the greatest chance of success and we designed an experimental matrix of parts to build and test.

Acousto-Optic performance at high temperature for our new HT AO device. While our first baseline tests resulted in failure below 100°C, the optimized design operated with little change for more than a week at 185°C.
Acousto-Optic performance at high temperature for our new HT AO device. While our first baseline tests resulted in failure below 100°C, the optimized design operated with little change for more than a week at 185°C.

Ilminster defined the orientations and dimensions of the samples and Palo Alto fabricated the substrates. Since the sites have different bonding expertise, both bonding and testing were carried out at both locations. In the first round, parts were fabricated with standard materials and processes, and both transducer and substrate showed cracks at temperatures as low as 75°C. In the second round both sites optimized the most successful variants and demonstrated solutions which survived the 175°C heat cycling tests with minimal transducer cracking and no evidence of cracking propagation into the substrate. The best designs were then used to fabricate working devices, and these were successfully thermally cycled to 175°C. One device was then tested actively at high temperature while monitoring the Acousto-Optic performance. The results of this test are graphed in Figure 1. The device performed excellently for one week each at 150°C, 175°C and 185°C without significant variation in the performance. Testing continued for 3 day cycles at 195°C and 205°C. By 205°C, though the diffraction efficiency (DE) had not dropped significantly, the power required to achieve that DE had increased by 50% and cracks had started to propagate into the substrate from the corners. This then was defined as the failure temperature.

G&H has demonstrated significant improvements in AO device reliability at high temperatures. This development was a project where we made full use of all the skills and experiences at our different sites. We had more effective and rapid development with this cross-site collaboration than could have been achieved by the sites individually, and the result was a hybrid solution using the best ideas from across the company.

For further information please contact Rob Swain at rswain@goochandhousego.com.