Absorption losses in MgO-doped and undoped potassium niobate

Abstract

Measurements of absorption losses in KNbO3 and MgO-doped KNbO3 were made in the blue and near-infrared wavelength regions using laser calorimetry. In the doped samples, the absorption loss for blue light was found to be 40% lower than that of the undoped samples. An enhancement in the infrared loss, caused by the presence of blue light, was observed in doped and undoped samples, but found to be much greater in the MgO-doped crystals. The blue-enhanced infrared absorption was characterized using two-wavelength laser calorimetry. Temporal variations in the second-harmonic power, caused by nonuniform heating of the active volume by the absorbed infrared and second-harmonic power, are described.

Compact all-solid-state source of polarization-entangled photon pairs

“…Furthermore, the power of the generated blue light shows oscillations when varying the cavity length, which are likely due to effects caused by blue enhanced infrared absorption. 12 Similar instabilities in KNbO 3 at these particular short wavelengths have been reported previously. 13 Stable operation could be achieved by changing the external crystal temperature 1.5 K below the phase-matching temperature.…”

Two-photon absorption in potassium niobate

“…Earlier work on the linear absorption coefficient for KNbO 3 [7] found α = 0.001cm −1 = 0.1m −1 at 860 nm. This value is much higher than this work.…”

“…Not only is the blue light itself absorbed by the crystal, it also significantly increases the absorption of the infrared light. This is called "blue-lightinduced-infrared-absorption" (BLIIRA), and it has been studied at length in the literature [7,11,12,13]. Previous work has found BLIIRA to be significant at blue light intensities down to 7 × 10 −4 W/cm 2 .…”

Phase-matching temperature shifts in blue generation by frequency doubling of femtosecond pulses in KNbO_3

“…We find that the optimum phase-matching temperature depends significantly not only on the input power but also on the focusing, which is attributed to the heating of the crystal that results from nonlinear absorption. As was pointed out for the cw experiments, 18,19 the heating effect that results from absorption of both fundamental and SH waves in a NLC deteriorates the conversion efficiency for high input powers. Polzik and Kimble 4 theoretically calculated a radially varying temperature distribution within the crystal driven by the absorbed power.…”

“…This saturation and nonlinear absorption are most likely related to a blue-induced IR absorption in KNbO 3 previously measured in cw laser experiments. [17][18][19] However, the possibility of an addi-tional nonlinear absorption effect owing to two-photon absorption arising from the high intensity of the femtosecond pulses is not excluded.…”