Patent ID: 7535937

Claim:
A monolithic microchip laser that produces low-noise blue light comprising: a birefringent crystal, selected from the group including TiO 2 ,un-doped YVO 4 , and other crystals in which the refractive indexes for the e-ray and o-ray are substantially different; a first gain medium which is an a-cut neodymium doped crystal anisotropic in respect of emission polarization and end-pumped by a first pump light to generate the first fundamental wave based on the polarized laser transition 4 F 3/2 → 4 I 9/2 ; a second gain medium which is an a-cut neodymium doped crystal anisotropic in respect of emission polarization and end-pumped by a second pump light to generate the second fundamental wave based on the polarized laser transition 4 F 3/2 → 4 I 11/2 ; and a nonlinear optical crystal in which the two fundamental waves are collinearly combined and intracavity sum frequency mixing of the first and second fundamental wavelengths takes place; wherein: the birefringent crystal is cut in such a way that the angle between its optic axis and the normal to the crystal surface, is π/4 or 3π/4; the birefringent crystal is sandwiched in between the two gain media and the nonlinear optical crystal with optical bonding at the interfaces; the two gain media are optically bonded to each other and are oriented with mutually orthogonal optic axes (C-axis), whereby one fundamental wave is an e-ray in the birefringent crystal and the other is an o-ray; the exterior surface of the first gain medium, where the first pump beam enters, is coated highly reflective to the first fundamental wavelength, anti-reflective to the first pump wavelength, and highly transmissive to the wavelengths corresponding to the laser transitions 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 ; the exterior surface of the second gain medium, where the second pump beam enters, is coated highly reflective to the second fundamental wavelength and is anti-reflective to the second pump wavelength; the interface between the birefringent crystal and the nonlinear optical crystal is coated highly transmissive to the first and second fundamental wavelengths and is highly reflective to the blue wavelength generated from the sum frequency mixing in the nonlinear optical crystal; the exterior surface of the nonlinear optical crystal is a mirror common to the first and second resonant cavities, it is highly reflective to at least one of the fundamental wavelengths and is highly transmissive to the blue generated from the sum frequency mixing in the nonlinear optical crystal; the two pump lights are split from a single light source and are substantially parallel to each other and are separated by a distance equal to the birefringent crystal length multiplied by the tangent walk-off angle; the intensity ratio of the first and second pump lights is greater than one.