Distributed feedback lasers, amplified

The first dye laser generates 10-ps, 2-pJ, 365-nm pulses that pump a microscopic distributed feedback dye laser (DFDL) producing Fourier transform hmited 0.7-ps pulses at 616 nm. These DFDL pulses are amplified in two stages to give 100-pJ, diffraction-limited pulses. 

An alternative way is to use a ps laser pumping a distributed feedback dye laser. Such a system with two amplifier stages is shown in Fig. 4. By using a quenched distributed feedback system short pulses can be obtained even with a ns pump laser [39]. 

Distributed Bragg reflector (DBR) and distributed feedback (DFB) fiber lasers have relatively short cavities, e.g., 10 cm or less, facilitated by the use of heavily doped-fiber amplifiers. The aim is to provide increased cavity mode... 

FIGURE 7 Schematic of a distributed feedback (DFB) fiber laser, including a power amplifier to boost the laser s output power. 

Although many diode lasers work as multimode lasers, the distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers show a mode selection because of their periodic structure. The mode selectivity is generated by the optical properties of the periodic stmctures because (Mily the modes that are associated with a standing wave/stop band are amplified. DFB structures are photonic structures, which are doped throughout the volume with chromophores (in an optimal case at the maxima of the standing waves), whereas DBR lasers have a miniature Fabry-Perot cavity in which the dye is localized, and the mirrors are replaced by periodic gratings [85]. 

Lasers have three primary components (Fig. 4) 1) an active medium that amplifies incident electromotive waves 2) an energy pump that selectively pumps energy into the active medium to populate selected levels and to achieve population inversion and 3) an optical resonator, or cavity, composed of two opposite mirrors a set distance apart that store part of induced emission concentrated in a few resonator modes. A population inversion must be produced in the laser medium, deviating from the Boltzman distribution thus, the induced emission rate exceeds the absorption rate, and an electromotive wave passing through the active medium is amplified rather than attenuated. The optical resonator causes selective feedback of radiation emitted from the excited species in the active medium. Above a pump threshold, feedback converts the laser ampler to an oscillator, resulting in emission in several modes. 

Because the laser effect is a special case of ASE where feedback occurs, the necessary conditions on 72 are the same as for ASE and are only given by eq. (108). This stringent condition is so weak that it is always fulfilled, and books about lasers do not even need to mention the existence of (Roess 1969, Weber 1979, Kaminskii 1981). It is so much the case that at room temperature, T2 is reduced to a few tens of picoseconds by phonon interaction. On the other hand, because of the multifold nature of the laser cavity, Tg is now the photon lifetime in the cavity, which is much larger than the travelling time in a distributed amplifier. It is given now by... 

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