We are using laser damage test systems on a production scale to scan large castings of laser glass for the presence of damage-causing platinum inclusions. These systems support glass melting production lines at two plants; one is in the U.S. (Schott Glass Technologies, Inc.) and the other is in Japan (Hoya Corporation). The damage test systems are designed to scan an entire glass casting using the pulsed output from a commercial Nd:YAG laser. The system is fully automated and operates unattended. Following testing, the glass casting is removed from the system and visually inspected for the presence of Pt-damage sites. We routinely test polygonally-shaped castings that are about 0.5 meter in size, weigh approximately 30 kg and contain about 7 liters of glass. It takes roughly 6 to 8 hours to test a piece of this size. To date the systems have been in use about 12 hours-per-day, up to 5 days-a-week for a period of about 15 months. Of the approximately 300 disks that have passed the damage test so far, sixty-two percent of the disks have no platinum inclusions at all and ninety-two percent have an inclusion density of less than 0.2 per liter.

Most glass optical components for high power leers are melted and homogenized in platinum-lined crucibles leading to the potential presence of microscopic platinum inclusions. In situations where large optics are exposed to high laser fluences, a significant problem can be creat 4 by an extremely low density of inclusions, as low as one per component. Previously, direct visual examination or optical microscopy was used to inspect for these particles, limiting reliable detection to Inclusions greater than 10ym diameter. Unfortunately, much smaller inclusions can initiate damage in modern lasers operated at high fluences. A test facility is described which detects small opaque Inclusions in large transparent components by using a commercial laser which delivers high energy pulses to the test sample at moderate frequency in » small diameter beam. The sample is automatically scanned such that each point in the volume is irradiated with ten pulses at twice the inclusion damage threshold-an amount sufficient to cause visible damage at inclusion sites. This approach permits detection of opaque inclusions 1n the parts per trillion and lower concentration range. The specifics of the device design, and its performance are discussed in the context of automatic inclusion inspection and mapping in large laser optics.