The present invention relates to an optical parametric oscillator including a non-linear optical crystal and two glass substrates surface contacted to the opposite ends of said crystal. The substrates include mirrors on their outer surfaces so that the combination of the mirrors, substrates and the crystal functions as the parametric oscillator. The invention also relates to the method of producing such an oscillator that overcomes the problems of surface contact bonding and laser damage threshold by use of an alkaline polishing compounds on the crystal ends.