Lasing Droplets: Highlighting the Liquid-Air Interface by Laser Emission

Abstract

When dye-doped ethanol droplets are irradiated with an intense pulsed laser beam, the resulting laser emission from individual droplets highlights the liquid-air interface. Photographs of the lasing droplets in the micrometer size range taken in a single 10-nanosecond laser pulse clearly show the dynamic changes in droplet size, shape, and orientation.

Large spectral tuning of a water–glycerol microdroplet by a focused laser: characterization and modeling

“…Considering a microdroplet radius of 4 mm, the spectral shift is predicted to be Dl E 0.0004-0.0008 nm using the asymptotically linear relationship between the spectral position of the whisperinggallery modes (WGMs) and the normalized equatorial radius (Dl = lDr h /r h ). 17,18 This spectral shift is much smaller than the 0.17 nm spectral resolution of the experimental setup. 8 We thus conclude that the deformation due to the optical scattering force cannot be the main mechanism for the spectral shifts observed in the experiments of Kiraz et al 8 Note that this theoretical result is consistent with the recent experimental observations reported by Kiraz et al 9 …”

“…The calculations in Fig. 2b use the asymptotically linear relationship between the spectral position of the WGMs and the normalized equatorial radius, 17,18 and they are valid for WGMs at around 590 nm irrespective of the size of the microdroplet. The range of temperature differences in this Figure corresponds to that caused by laser heating used in our experiments, as will be discussed in section V. Note that the results plotted in Fig.…”

Optofluidic dye lasers

“…In such microspherical cavities, light is confined by continuous total internal reflections at the liquid-air interface, and forms the so-called whispering gallery modes (WGMs). Dye lasing has been demonstrated in free falling droplets (Tzeng et al 1984;Qian et al 1986), pendant droplets (Hansch 2005) and levitated droplets (Tona and Kimura 2000;Azzouz et al 2006). Although the observation of dye lasing in droplets dates back to the 1970s (Hansch 2005), the first reported microdroplet dye laser in the literature was by Chang's group (Tzeng et al 1984;Qian et al 1986).…”

“…Dye lasing has been demonstrated in free falling droplets (Tzeng et al 1984;Qian et al 1986), pendant droplets (Hansch 2005) and levitated droplets (Tona and Kimura 2000;Azzouz et al 2006). Although the observation of dye lasing in droplets dates back to the 1970s (Hansch 2005), the first reported microdroplet dye laser in the literature was by Chang's group (Tzeng et al 1984;Qian et al 1986). In this work, dye solution droplets were generated by a vibrating orifice, in which a cylindrical liquid jet passing through the orifice is induced to break up into equal-sized droplets by a mechanical vibration of the orifice with the proper frequency and amplitude (Tzeng et al 1984;Lin et al 1990).…”

“…However, there existed micron-sized liquid dye lasers long before the advent of microfluidics which also satisfy our definition of optofluidic dye lasers, such as microdroplet dye lasers (Qian et al 1986), microcapillary dye lasers (Ippen et al 1971), and evanescent gain microsphere (An 2001;An and Moon 2003) and fiber lasers (Pendock et al 1992) immersed in dye solutions. Here, we review both the recent efforts of building on-chip microfluidic dye lasers and some of the pre-microfluidics era dye lasers with micron-scale dimensions, which are also amenable to microfluidic implementations and have potentially interesting applications.…”