Page 210 - Tunable Lasers Handbook

188 F. J. Duarte

Stainless
Brewster
Angle Prism
Argon Laser Beam
514.5 nm

Dye Laser
Beam
FIGURE 1 1 Linear cw dye laser cavity configuration. (Reprinted 41th permission from Tuccio
and Strome [XI.)

to induce heat dissipation and hence reduce thermally induced optical inhomo-
geneities in the active medium [85].
Widely used configurations of cur dye laser cavities include the three-mirror
folded linear cavity (see, for example, [20] and references therein) and ring-dye
laser cavities (see, for example, [3] and references therein). These two configura-
tions are shown in Fig. 12. In both cases excitation from a cw laser is accom-
plished semilongitudinally to the optical axis defined by M, and M,. Tuning ele-
ments. or frequency-selective elements (FSEs), are deployed between h/I, and
M, in the linear cavity, and between M, and M, in the ring cavity. The unidirec-
tional device (UDD) depicted in Fig. 12(b) is an optical diode that controls the
direction of propagation in the ring cavity [3].
Ring-dye laser cavities circumvent the problem of spatial hole burning associ-
ated with linear cavities [3]. Also ring cavities are reported to yield higher single-
longitudinal-mode power than linear cavities [3]. However, linear configurations
offer greater optical simplicity and lower oscillation thresholds.
Diels [87] discusses the use of propagation matrices, applicable for Gauss-
ian beam propagation analysis, to characterize stability conditions and astigma-
tism in cw dye laser cavities.
Linewidth narrowing and FSEs used in cw dye lasers are birefringent crys-
tals. prisms, gratings, and Fabry-Perot etalons. Often two or more FSEs are nec-
essary to achieve single-longitudinal-mode oscillation. The first stage in the fre-
quency narrowing usually consists of utilizing prisms or birefringement filters to
yield a bandwidth compatible with the free spectral range (FSR) of the first of
two etalons. In turn, the second etalon has a FSR and finesse necessary to restrict
oscillation in the cavity to a single-longitudinal mode [3]. Alternative approaches
may replace the second etalon by an interferometer [88]. The performance of var-
ious linear and ring cw dye lasers is listed in Table 12.