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Piezo actuator Thin etalon BRF C Jet Thick etalon Pump M (a) Faraday rotator Polarization rot. Pump M M C (b) Figure 7. Schematic diagrams of CW dye laser illustrating (a) standing wave resonator with spectral filtering and tuning elements; (b) unidirectional ring resonator (filter and other optical elements for astigmatism compensation and cavity length change are not shown). C—output coupler. M—mirror. BRF—birefringent filter. CW Narrowband Dye Lasers Design considerations for CW dye lasers (1,2) differ considerably from those for pulsed dye lasers.

6 is therefore schematic in nature, and R may be considered as a generalized vibrational coordinate. The minimum energy for exciting an electron in ;; ;; ;;; ;; ;; T2 IC TR ESA, α 12 Potential energy CH3 (2) T-T Abs S1 ISC T1 IC TR TR Abs. Emission, σ0 σ e, τ S0 R Figure 6. Conceptual depiction of potential energy curves and physical processes influencing laser action. Abbreviations and symbols are explained in text. Cross sections associated with the processes involved in the model discussed are designated by ␴ with appropriate subscripts.

In the electronically excited state, S1, the electron cloud is slightly expanded and exerts less binding force on the nuclei. As a result, the equilibrium separation of the nuclei corresponding to the minimum of the potential well is larger than in the ground state. The triplet states have lower energy than the corresponding excited singlet states. According to the Pauli exclusion principle, no two electrons can have the same spatial, momentum, and spin quantum numbers simultaneously. Hence, on average, wavefunctions of electrons in triplet state with parallel spins have less spatial overlap than those with antiparallel spins in the singlet state.