High-efficiency second-harmonic generation at 4250-4680 Å in KNbO3

KNbO
3
has been found to be noncritically phase matchable for frequency doubling of 8500-9360-Å radiation by temperature tuning. An energy conversion efficiency of 43 percent was obtained at a pump power of 0.9 MW at 8502 Å in a 5-mm-long crystal, thus demonstrating the attractiveness of KNbO
3
as a second-harmonic generator of moderate to low power near-infrared lasers such as an Er: YLF laser.