A long-lived UV laser is an enabling technology for several high-priority, space-based lidar instruments. These include a next generation cloud and aerosol lidar that incorporates a UV channel, a direct detection 3-D wind lidar, and an ozone differential absorption lidar (DIAL) system. To advance the TRL of UV lasers we have designed and built a High Energy UV Demonstrator (HEUVD) that has increased output power and space-qualifiable packaging and that is mechanically robust, thermally-stable, and fully conductively cooled. Contamination control processes and optical coatings have been chosen that are compatible with multi-billion shot lifetimes. The diode pumped laser contains an essentially polymer free internal module that houses the third harmonic generator and beam expansion optics. When operated at 150 Hz the laser has demonstrated 275 mJ per pulse at 1064 nm, second harmonic conversion efficiencies of 70%, and third harmonic conversion efficiencies of 45%, thus meeting the 355 nm 100 mJ/pulse goal with margin. We have successfully completed a full power 532 nm life test, a half power (50 mJ/pulse) UV lifetest, and a full power (100 mJ/pulse @ 150 Hz) lifetest. These tests have validated the importance and success of our approach to contamination control for achieving a long-lived UV laser. They also resurfaced the need for the qualification of the pump laser diodes and more attention to the external optics in a UV lidar system.
A long-lived UV laser is an enabling technology for a number of high-priority, space-based lidar instruments. These
include next generation cloud and aerosol lidars that incorporates a UV channel, direct detection 3-D wind lidars, and
ozone DIAL (differential absorption lidar) systems. In previous SBIR funded work we developed techniques for
increasing the survivability of components in high power UV lasers and demonstrated improved operational lifetimes. In
this Phase III ESTO funded effort we are designing and building a TRL (Technology Readiness Level) 6 demonstrator
that will have increased output power and a space-qualifiable package that is mechanically robust and thermally-stable.
For full space compatibility, thermal control will be through pure conductive cooling. Contamination control processes
and optical coatings will be chosen that are compatible with lifetimes in excess of 1 billion shots. The 1064nm output
will be frequency tripled to provide greater than 100 mJ pulses of 355 nm light at 150 Hz. The laser module build was
completed in the third quarter of 2015 at which time a series of life tests were initiated. The first phase of the lifetime
testing is a 532 nm only test that is expected to complete in April 2016. The 532 nm lifetest will be followed by a 4
month half power UV life test and then a four month full power UV life test. The lifetime tests will be followed by
thermal/vacuum (TVAC) and vibration testing to demonstrate that the laser optics module design is at TRL 6.