Abstract

We have doubled the tuning range of a passively mode-locked NaCl color-center laser by introducing a low-loss intracavity frequency filter and properly preparing the NaCl gain crystal. By using a collection of bulk and multiple-quantum-well III–V saturable absorbers and II–VI quantum-well saturable absorbers, we obtained passive mode-locked operation over the wavelength range of 1.5–1.7 µm. To provide sufficient wavelength restriction without introducing excess bandwidth limiting or loss, we replaced the biréfringent plate of previous systems¹ with a tunable frequency filter,² formed by a pair of equilateral flint glass prisms (spaced 22 cm apart) and followed by a knife edge. We tune the laser by horizontal translation of the knife edge. The laser produces pedestal-free, near-transform-limited 280 fs pulses, which is the same pulse width obtained with birefringent plates. To obtain lasing at wavelengths shorter than 1.51 µm, the NaCl YAG crystal must be annealed to reduce scattering from presence of colloidal particles formed during coloration. With annealed crystals we obtain lasing at wavelengths as short as 1.38 µm, and laser power at 1.5 µm is only 30% below the maximum. In summary, we demonstrate a stable, single-cavity solidstate, subpicosecond pulse source of 1.5–1.7 µm.

© 1990 Optical Society of America