Mode-locking techniques

Organic dye lasers are especially useful for nanosecond absorption spectroscopy since their wavelength can be tuned continuously over a range of several hundred angstroms and their output pulses reach several megawatt at pulsewidths down to 10" sec with mode-locking techniques. 

During the last decade, solid-state lasers captured the market and substituted the complex dye systems more and more (Fig. 1). The breakthrough for solid-state femtosecond oscillators was connected with the development of the Kerr lens mode-locking technique for the Tiisapphire laser [7]. The simple Tiisapphire cavity contains the active medium (Tiisapphire rod) and dispersive elements. Kerr lensing in a Tiisapphire rod develops due to an intensity-dependent refractive index across the spatial beam profile yielding a self-focusing of the laser beam. With an additional aperture in the beam... 

Fig. 2 Kerr lens mode-locking technique for the Ti sapphire laser...

Yin K, Zhang BB, Yang WQ, Chen H, (Then SP, Hou J (2014) Flexible picosecond thulium-doped fibCT laser using the active mode-locking technique. Opt Lett 39 4259-4262... 

Table 6.1 Summary of different mode-locking techniques. With an average power of 1 W can be achieved...

Several new mode-locking techniques have recently been introduced that provide subpicosecond pulses from color center lasers. The first method uses passive modelocking through the introduction of a suitable semiconductor saturable absorber in the laser cavity. To date, 200-fsec pulses have been generated at fixed wavelengths in the 1.5- and 2.7-/xm region. 

Hybrid mode locking techniques combine the best features of other mode locking methods. For example, an active mode locking element may be inserted into a passively mode locked fiber laser cavity to produce an ultrashort pulse laser with well-defined repetition rate. Similarly, semiconductor saturable absorbers may be inserted into passively mode locked fiber lasers to initiate soliton generation, resulting in an ultrashort pulse laser with low selfstarting threshold. 

Singh, S. Short pulse generation from a flashlamp-pumped Rhodamine 6G ring dye laser using the colliding pulse mode-locking technique. Appl. Opt. 1987,26,66-69. 

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