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We report on fabrication of ultrahigh-Q crystalline optical whispering gallery mode (WGM) resonators via mechanical polishing. The maximum Q-factor achieved at room temperature exceeds 2×1010. We discuss strong nonlinear behavior of the resonators and propose several devices based on the resonators. We have studied WGM resonators fabricated of calcium fluoride and few other crystals and measured their quality factors. High optical Q-factor was obtained due to several nonlinear optical effects. Two of them are instability due to strong thermal nonlinearity and optical oscillations based on four wave mixing.