Light amplification shifts

Delayed emission and shift in frequencies constitute basic features of lasers (which is an acronym for Light Amplification by Stimulated Emission of Radiation) also. Glasses are used as hosts for lasers and Nd laser in phosphate glass hosts has been in wide use (Snitzer, 1989). The principle of operation of Nd laser is shown in Figure 11.12 and typifies a... 

One advantage of polymers which is especially useful for laser-oriented applications is the red shift in the luminescence spectrum in comparison with their absorption. This phenomenon gives the opportunity of light amplification without losses caused by self-absorption in active media. Many efforts are now being concentrated on the manufacture of electronically pumped polymer lasers, although they have not yet met with success. 

The high sensitivity of lock-in amplification can be applied to detect the small periodic changes in transmittance caused by modulated e.xcitation with UV light. Measurements of the amplitude and phase shift of the response signal allow us to determine the spectra and lifetimes of the transient species. 

According to Fig. 20 and the pertinent discussion, besides the light-shifted absorption line also an ampUfication hne should appear for a non-resonant pump beam. Actually, in the single molecule fluorescence excitation experiments population changes are measured and the amplification effect is expected to be very weak. Due to the large scattering background induced by the pump it was not observed so far. 

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