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We report synchronously mode-locked subpicosecond and continuous-wave color-center laser operation in the 1.8–2.4-μm wavelength range. For active materials we use (F_2^+)H centers in KBr:O_2^− and (F_2^+)AH centers in KBr:Na^+:O_2^− crystals. When the lasers are pumped with a continuous-wave or mode-locked NaCl (F_2^+)H-center laser in a cascaded configuration, laser operation is obtained over the combined tuning range of 1.8–2.4 μm, with output powers as high as 150 mW. When synchronously mode locked with ~5-ps pump pulses, both KBr lasers yield typically ~1-ps pulse widths over the entire tuning range. Pulses as short as ~400 fs could be obtained at the expense of higher noise levels.

We report the production and main optical and laser properties of (F_2^+)H color centers in sulfur-doped NaCl crystals. Using a 1.06-μm Nd:YAG laser as the pump source, we realize continuous-wave and synchronously mode-locked laser operation. The laser is tunable over a remarkably large wavelength range of 1.43–2.0 μm. Output power levels are as much as ~800 mW near 1.6 μm; mode-locked pulse durations are typically 4–7 ps.

We use coherent photon seeding to passively stabilize a synchronously mode-locked NaCl color-center laser. This results in the generation of essentially transform-limited picosecond pulses with average power levels of as high as 1.3 W in the 1.5–1.7-μm range. In addition, the pulse energy fluctuations are reduced by as much as 1 order of magnitude.

We report new ultrafast color center lasers operating in the near infrared spectral range. Using newly developed KCl and KBr (F2+)H and (F2+)AH color center systems and synchronous mode-locking we realize picosecond and subpicosecond color center laser operation for the first time in the 1.8-2.4 μm wavelength range. Using semiconductor saturable absorbers we passively mode-lock NaCl (F2+)H and KCl FA (Tl) color center lasers in single- and coupled-cavity configurations. This results in mode-locked laser operation in the 1.5-1.7 μm range with shortest obtained transform-limited pulses of ∼ 150 femtosecond duration and pulse energies as high as several nJ. As a step toward infrared spectral continuum generation we amplify these nJ-level pulse energies by a factor of ∼ 103 using KCl FA(Tl) amplifier crystals.

By using a bulk InGaAsP saturable absorber, we passively mode lock a KCl F_A(Tl) color-center laser in a resonator configuration where the gain material is placed in a main cavity and the saturable absorber is placed in a weakly coupled external cavity. We obtain self-starting and self-stabilized resonant passive mode-locked laser operation, either with pulses as short as ~320 fs or average output power as high as ~380 mW. The pulse width-bandwidth product is ~0.47, with pulse energies of as much as 2.5 nJ. By temperature tuning the saturable absorber band edge, we realize laser operation with similar performance over the wavelength range of 1.50–1.55 µm. When compared with mode-locked KCl F_A(Tl) laser operation, where both the gain material and the saturable absorber are placed in a common single cavity, the resonant passive mode-locking technique yields pulses with only moderately increased widths (by ~50 fs) but significantly higher energies (by a factor of ~4).