Noncritically phase-matched sum frequency generation and image up-conversion in KNbO3 crystals

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Abstract
Tunable and continuous wave (cw) near infrared up‐conversion into the dark blue wavelength range (410–465 nm) has been achieved in KNbO3 crystals using the nonlinear optical coefficient d32 (ω1+ω2; ω1,ω2)=20.4 pm/V. High efficiencies have been reached due to the large nonlinearity and the possibility of temperature‐tuned noncritical 90° phase matching. Using a neodymium:yttrium aluminum garnet laser (1064.2 nm) as the signal source and a krypton laser (676.4 nm) as the pump source, a sum signal (413.6 nm) power of over 0.1 mW was reached at a pump power of only 26.2 mW. cw image up‐conversion into the blue wavelength range has been demonstrated using a noncritically phase‐matched configuration in the same crystals at T=−4 °C.