Improved nonlinear coefficient (0.7 pm/V) in silica thermally poled at high voltage and temperature

It is shown that in thermally poled silica a substantially increased second-order nonlinearity is induced when both the poling voltage and the temperature are increased under standard poling conditions (~275°C/~5 kV). Increases in the voltage result in a nonlinear region with a greater width and buried depth, while increases in the temperature enhance the peak nonlinear coefficient d₃₃. In a silica sample poled at 400°C and 20 kV, a nonlinear region 10 μm deep was measured with a d₃₃ of 0.7 pm/V which is twice as large as that for a sample poled under standard conditions, and the highest reliable reported value