Low noise blue laser by frequency doubling a diode laser

Summary form only given. Coherent CW blue lasers are considered attractive for many applications, particular spectroscopy. One efficient method to generate blue light with a broad tunable wavelength range is second-harmonic generation (SHG) of a near-infrared diode laser using a KNbO/sub 3/ crystal in an external resonator. Passive optical feedback is often employed to lock the frequency of the single-longitudinal-mode diode laser to the resonance of the external cavity for stable and efficient SHG, and to improve the spectral properties of the diode laser. We use a high-power Fabry-Perot (FP) diode laser by feeding back the transmission of the ring cavity into the laser after reflecting off a diffraction grating to obtain single-mode and self-locking to the ring cavity resonance with a narrow linewidth.