Sintering Ceramic Laser Materials with a High Power 83 GHz Beam
Abstract
Millimeter-wave processing (sintering) of ceramic laser host materials has been under investigation at the Naval Research Laboratory (NRL) for high energy laser (HEL) applications. Advantages of polycrystalline, compared to single-crystal laser host materials, include lower processing temperature, higher gain from higher dopant concentrations, cheaper fabrication, and larger devices. Millimeter-wave processing has been shown to be an effective alternative to conventional vacuum furnaces for pressure-free sintering of low-loss oxide ceramic materials. It involves direct volumetric heating of the workpiece. This often results in superior microstructure with fewer trapped pores, cleaner grain boundaries, and smaller grain size than conventionally sintered materials. These properties are critical to achieving high optical quality laser host materials. The absorbed power per unit volume in a ceramic is proportional to the microwave frequency. Thus the power loss is a function of both the temperature of the ceramic and the frequency; at a given frequency, oxide ceramics tend to be more absorbing at higher temperatures, and at a given temperature, an oxide ceramic is more absorbing at higher frequencies. The NRL gyrotron-based material processing facility features a 15 kW, continuous wave, 83 GHz GYCOM gyrotron oscillator, which can generate between 1 W/sq cm and 2 kW/sq cm irradiance. The facility features a quasi-optical beam system for beam focusing and manipulation and an inner vacuum chamber for atmosphere control and vacuum processing. The gyrotron is operated via a fully automated computerized control system written in the LabVIEW platform with feedback from extensive in-situ instrumentation and visual process monitoring. The system has the capability of sample rotation and translation during processing.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2008
- Accession Number
- ADA493127
Entities
People
- Arne W. Fliflet
- M. A. Imam
- Manfred Kahn
- Melissa Hornstein
- Steven H. Gold
Organizations
- United States Naval Research Laboratory