Lasing single-mode

Figure 10-14. Inset Phololumincsccncc spectrum for low excitation pulse energy EP Main part (a) displays the spectrum for pump pulse energies well below the lasing threshold while (b) shows the spectrum obtained lor excitation with a pump energy close to the lasing threshold (c) presents the single mode-lasing spectrum emitted when the device is pumped well above threshold. The dashed lines indicate the zero line which is arbitrarily shifted in case of (b) and (c).

Figure 10-15. Output vs. input energy characteristic of our laser device. The horizontal dashed curve indicates the zero line. A clear laser threshold behavior at an excitation pulse energy ol 1.5 nJ is observed. Below the lasing threshold only isotropic phololuminesccncc is entitled. Above threshold the device emits low divergence single mode laser emission perpendicular to the surface, as schematically shown in the inset. The laser light is polarized parallel to the grating lines.

Recently, even practically, single-mode lasing of a droplet has been reported for quantum dot doped droplets14, when the droplet diameter was sufficiently small and pump laser intensities were high enough as shown in Fig. 17.10. Interestingly, the... 

Fig. 17.10 Schafer et al.14 have observed single mode lasing from core shell CdSe/ZnS nano crystal quantum dots in a glycerine water mixture. The fluorescence spectrum (black line) showed clear peaks of WGM and single mode lasing (grey line) was observed for sufficiently small droplets ( 10 pm) and high pump laser intensities (53 mJ crrT2 in 10 ns pulses at 532 nm). Insert shows the droplet trapped between the electrodes. Reprinted from Ref. 14 with permission. 2008 American Chemical Society...

Schawlow-Townes equation The equation which predicts theoretically the linewidth of the lasing transition of a single-mode laser. The linewidth predicted from this equation is inversely proportional to the output power and the cavity quality factor (Q-factor). 

When the threshold condition for lasing Ai > A2 -f- 1 is fulfilled, where Ai = G A plq, A2 = —G2A2p/q, the spatially homogeneous steady-state solutions /o, A/o of Equations (44) correspond to single-mode CW laser operation. They have the form... 

Tona, M. Kimura, M., Novel lasing modes observed in a levitated single dye doped micro droplet, J. Rhys. Soc. Jpn 2000, 69, 3533 3535... 

Population inversion is often achieved by a multi-level atomic or molecular system in which the excitation process, called pumping, is accomplished by electrical means, by optical methods, or by chemical reactions. In some cases, the population inversion can be sustained to produce a continuous wave (CW) output beam that is continuous with respect to time. In other cases, the lasing action is self terminating, so that the laser is operated in a pulsed mode to produce a repetitive pulse train or a single-shot action. ... 

Many times it has been found that more than a single series of longitudinal modes survives lasing in microdisks. In such cases it was found that a careful FT helps to separate the contributions of the different modes series. An example of this complication is given below. Figure 22.38a [123] shows the emission spectrum for the 55-p,m diameter microdisk laser measured above the threshold intensity. There are many well-spaced and narrow emission lines. A closer examination of the spectrum reveals two series of modes, one series, a, has larger amplitude than the other, b. For the larger intensity peaks. 

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