We perform a theoretical study to determine an optimal crystal thickness and operating temperature in sum-frequency generation by using commonly-used nonlinear crystals such as lithium barium borate, beta barium borate, and potassium titanyl phosphate. The optimal thicknesses of those crystals to avoid any decrease in the yield due to interference originating from different path lengths between the two pump pulses are calculated as functions of the fundamental intensity and the pulse width.

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... tionally, the fluctuation of the sum-frequency generation yield with temperature, which introduces a refractive-index change, is calculated, and the temperature ranges giving low fluctuations in the yield are demonstrated in room-temperature operation.