Lasing transitions for

Ptutoyujum. (Am +). The energy level scheme and possible lasing transitions for Pu + are very similar to those of Np +. Prospective transitions include 6Hg/2+6H5/2, 9/2 7/2, and h7/2 Hc/2 For efficient fluorescence and laser action from either tne °Hg/2 or j/2 states, hosts should have low phonon frequencies to reduce nonradiative decay by multiphonon processes. Depending upon the host and the exact positions of higher-lying states, excited-state absorption may reduce or prevent net gain. 

The development of up-conversion fiber lasers, especially in the visible, is assisted by the availability of intense semiconductor lasers and mini-crystal lasers for pump sources. The various energy levels involved in pumping and lasing transitions are detailed in Sec. 8.4 and in related energy level diagrams. 

Since the demonstration of the first THz QCL in 2002 [8], it has been much more difficult to achieve room temperature operation than for mid infrared devices. The main reason for this is that dephasing and scattering phenomena can lead to level broadenings of the same order of magnitude of the lasing transitions, making population inversion by carrier injection in upper lasing subbands extremely difficult. 

The familiar 632.8 nm output of the He-Ne laser is available in several integrated Raman spectrometers of analytical interest. Unlike ion lasers, the lasing transition in the He-Ne is an atom (neon), so power need not be consumed to create excited ions. Helium ions and electrons carry the current in the He-Ne laser tube, but energy is transferred to Ne atoms before lasing, and the process is much more efficient than that of ion lasers. Ordinary 110 V electrical power and air cooling are sufficient, and He-Ne lasers are generally much smaller (and less expensive) than ion lasers. However, the output optical power is much lower for the He-Ne laser compared to Ar+ lasers, with the common... 

An analysis of the calculated transition dipole moments of the APSS molecule shows that only transitions between the singlet Sq, Sj and S, states dominate in the nonlinear optical process of interest (see Fig. 2) and we therefore restricted our simulations to comprise these three states. To explain the observed delay between the ASE and pump pulses, we need to take into account the vibrational structure. We model this structure for the levels Sj and Sq by including two pairs of vibrational levels, (4, 3) and (2, 1), respectively, making use of the one-mode approximation. The vibrational levels 3 and 1 are the lowest vibrational states for the electronic states Sj and Sq, respectively (Fig. 2). The vibrational state 4 models the group of vibrational states nearby the vertical photoabsorption transition Sq -> Sp Apparently, the vertical transition has larger probability. The lasing transition takes place from the vibrational level 3 to the vibrational level 2 which corresponds to the vertical decay Si -> So (Fig. 2). The transition matrix element is a product of the electronic matrix element and the Franck-Condon amplitude between vibrational states v and t ... 

Figure 1. Representative energy-level diagram and transitions for four-level and cascade lasing schemes vP and vL are the pump and laser frequencies wavy lines denote nonradiative transitions.

We consider only f-f transitions for lasing. The approximate positions of the 6d and charge transfer bands throughout the actinide series are known (98, 99). The 6d bands are lower than are the corresponding 5d bands of the... 

Fig. 5. Relative gain coefficients of HF for thermal rotational populations and different vibrational population ratios, X v)/X v- ). The heavy line is the loci of highest gain transitions. At every vibrational population ratio lasing occurs only on the highest gain transition for which is just above o . As X v)/X v— 1) decreases J increases provided that a decreases too. ...

Fig. 3.31. The ruby three-level laser. The pumping nansiiion is 1, the lasing transition 3. The nonradiaiive transition 2 is fast relative to the radiative inverse of 1. The level notations are for Cr +. The orders of magnitude of the relevant rates are p( T2 - Aj) = 10 s .

Fig. 3J2. The four-level laser scheme. Pumping transition is I, lasing transition 3, nonradiaiive uansitions 2 and 4. On the right-hand side the level notation for Nd for the case of the 1064 nm laser action is given. H denotes levels above F3/2 further I11/2 cannot be thermally populated since it is about 2000 cm above the ground state...

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