Speckle control using high-frequency signal superposition to semiconductor laser

Speckle contrast of images generated by a red semiconductor laser was measured precisely utilizing a state-of-the-art speckle measurement system with a cooled CCD camera with auto-light-power-level adjustments. By using high-frequency signal (～500 MHz) superposition to the single-mode semiconductor laser, the 3 dB spectrum of the laser beam was broadened from 0.1 to 2.3 nm. As a result, the speckle contrast value was drastically reduced from 0.9 to 0.2.