Optically tunable/switchable omnidirectionally spherical microlaser based on a dye-doped cholesteric liquid crystal microdroplet with an azo-chiral dopant

Abstract

This paper presents an optically wavelength-tunable and intensity-switchable dye-doped cholesteric liquid crystal (DDCLC) spherical microlaser with an azo-chiral dopant. Experimental results present that two functions of optical control - tunability of lasing wavelength and switchability of lasing intensity - can be obtained for this spherical microlaser at low and high intensity regimes of non-polarized UV irradiation, respectively. If the DDCLC microdroplet is subjected to weak UV irradiation, azo-chiral molecules may transform to the bent cis state at a low concentration rate. The effect can slightly decrease the local order of LCs and thus the helical twisting power of the CLC in the microdroplet. As a result, the CLC pitch may become slightly elongated, which will cause the gradual red-shift of both omnidirectional PBG and lasing emission of the DDCLC spherical microdroplet. In contrast, when the microdroplet is subjected to strong UV irradiation, numerous azo-chiral molecules may simultaneously change to bent cis-isomers to seriously disarrange the helical texture of the CLC, which will quickly deform the PBG and deactivate the lasing emission of the microdroplet. Prolonged irradiation of a blue beam after strong UV irradiation may cause the cis azo-chiral molecules quickly convert back rod-like trans-isomers, which may then regenerate the CLC Bragg onion and PBG structures and reactivate the lasing emission of the microdroplet. Optical control of the DDCLC spherical microlaser is realized on a scale of seconds and minutes when UV irradiation is strong and weak, respectively. The 3D DDCLC spherical microlaser is a highly promising controllable 3D micro-light source or microlaser (e.g., all-optical 3D single photon microlaser) for applications of 3D all-optical integrated photonics, laser displays, and biomedical imaging and therapy, and as a 3D UV microdosagemeter or microsensor.

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

“…A phototunable color cone lasing based on CLCs containing photoisomerizable chiral dopant of isosorbide 2,5‐bis 4‐methoxy‐cinnamate exhibited a continuous tuning of emission wavelength covering a spectral range larger than 100 nm, from the original reddish emission to the final green one in 160 s of UV exposure. Such wavelength could be tuned by inclining the cell regarding to the wave vector of pumping light as well . In addition, a water/oil/water system, containing the aqueous solution of polyvinyl alcohol (PVA) and photoresponsive CLCs, was elaborately prepared, forming a monodispersed CLC micro‐shell through the specific designed glass capillary microfluidic device .…”

Droplet lasers: a review of current progress

“…As the authors state, "The proposed procedure of making a CLC onion microlaser by mechanical mixing is simple and straightforward and produces millions of microlasers in a fraction of a second." The same type of CLC microdroplet lasers can be further improved by adding an azo-chiral dopant [118]. The dopant changes its isomerisation as it is illuminated with weak UV light, which has the effect of changing the interaction with the liquid crystal and altering the pitch of the CLC droplet (which, as indicated above, controls the laser output).…”

Optically pumped mirrorless lasing. A Review. Part II. Lasing in photonic crystals and microcavities

“…Notice that a photosensitive chiral azo-dopant has been used in Ref. [152] to tune the wavelength and switch the lasing intensity in the droplet dye-doped ChLC laser.…”