Lasers vibronic

Figure 2.17 A simplified energy-level diagram for a vibronic laser.

From the point of view of mechanical and optical properties vibronic lasers are connected to luminescent solar concentrators. 

A generalized energy level scheme for laser action is shown in Fig. 1. If the terminal laser level is the ground state and the initial and final laser states have equal degeneracies, then more than one-half of the ions must be excited to obtain an inverted population and 3-level laser action. If, instead, the terminal level 2 is above the ground state, then only an excited-state population in level 3 sufficient to overcome the Boltzmann population in level 2 is needed for population inversion. This drastically reduces the pumping requirements. Phonon-terminated or vibronic lasers are those in which level 2 is a vibrational-electronic state. 

The Ti sapphire laser is called a vibronic laser, because of the close blending of the Ti electronic and vibrational crystal-host coupling frequencies. A very reduced energy level diagram for the 3d Ti + ion... 

Fig. 5.72. (a) Level scheme of a tunable four-level solid-state vibronic laser (b) absorption spectrum for two different polarization directions of the pump laser (c) output power Pout (7.) for the example of the alexandrite laser... 

A particularly efficient cw vibronic laser is the emerald laser (BeaAliSiaOigtCr " ). When pumped by a 3.6-W krypton laser at Xp = 641 nm, it reaches an output power of up to 1.6 W and can be tuned between 720 and 842nm [5.131]. The slope efficiency dPout/dPin reaches 64% The erbium YAG laser, tunable around X = 2.8 p.m, has found a wide application range in medical physics. 

Table 5.3 compiles the operational modes and tuning ranges of different tunable vibronic lasers. A particularly efficient cw vibronic laser is the emerald laser... 

Andrews [9] and others [10] have listed the emission lines of the most commonly available discrete-wavelength lasers (such as ruby, Nd YAG, Er YAG, excimer lasers) over the range 100 nm-10 /u.m. Molecular lasers (HF, CO, CO2, NO) can be tuned to a large number of closely spaced but discrete wavelengths. Continuously tuneable lasers comprise some metal ion vibronic lasers (e.g. alexandrite and Ti sapphire [11]), some diode and excimer lasers, dye and free-electron lasers. Tuneable sources of coherent radiation span the electromagnetic spectrum from 300 nm to 1 mm, with limited tune-ability down to about 200 nm. Wavelength coverages of tuneable lasers have been reported [8]. In operation lasers can be either pulsed (e.g. various metal ion tuneable vibronic lasers, excimer and dye lasers, metal vapour) or continuous wave (major types atomic and ionic gas lasers, dye and solid-state lasers). Most lasers with spectral output in the UV are bulky and expensive devices (especially sub 200 nm) and operate in the pulsed mode. On the contrary, many visible lasers are available which are compact, require low maintenance expenses and operate in continuous-wave (CW) mode. 

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