Tunable Blue Laser for Holographic Data Storage

2. Emission section The tunable blue-laser system we report here consists of a micro computer, electric circuits, and the laser shown in Fig. 1. Figure 2 shows the inside of the laser, consisting of the emission section, the wavelength monitor and the mode hop monitor. The emission section consists of a laser diode (LD), a lens, a grating, a mirror and a motor. A Littrow-type laser is used to generate a single-mode ray. The LD’s multi-mode ray is collimated in the lens and diffracted on the grating. One of the first-order rays is selected by adjusting the angle of the grating and diffracted back to the LD, and the LD lases in a single mode of its wavelength. The incident angle and the diffracted angle are the same, and the angles θ are given by g λ θ = sin 2 (1)