Page 72 - Optofluidics Fundamentals, Devices, and Applications

Optical Components Based on Dynamic Liquid-Liquid Interfaces 53

50 nm 25 μJ
40 20
FWHM 30 15 Output pulse energy

10
20
10 5

0 0
0 20 40 60 80 100 120 140 μJ
Input pulse energy
(b)
640
Peak wavelength (nm) 630
635

625
620
615
610
0.0 0.2 0.4 0.6 0.8 1.0
Volume fraction of DMSO
(c)

FIGURE 3-12 (Continued)

Figure 3-12b is a plot of output power and line width as a function of
pump power. At low pump power (< 5 μJ/pulse) the line width (full
width at half-maximum, FWHM) of the emission is ~ 45 nm, with λ
max
centered at 625 nm. The line width drops to ~4 nm between pump pow-
ers of 7 and 16 μJ. The threshold for lasing occurs at 22 μJ pulse energy.
Wavelength Tunability
Like other dye lasers, the output wavelength can be changed by
changing the choice and volume fraction of the solvent for the dye.
Changing the solvent in the fluorescent core provides a simple way
to adjust the wavelength of emission for a given dye without incor-
porating dispersive elements (prisms or gratings) into the optical
cavity. For example, the wavelength of the light output for rhoda-
mine 640 shifted by more than 20 nm by changing the composition
of the core liquid; λ = 617 nm for methanol (MeOH), 631 nm for
max
ethylene glycol, and 634 nm for dimethyl sulfoxide (DMSO). Adjusting
the composition of a mixture of DMSO and MeOH in the core allows
continuous tuning of λ (Fig. 3-12c).
max