  Liquid-crystal microcavity lasers have attracted considerable attention
because of their extraordinary tunability and sensitive response to external
stimuli, and they operate generally within a specific phase. Here, we
demonstrate a liquid-crystal microcavity laser operated in the phase
transition, in which the reorientation of liquid-crystal molecules occurs from
aligned to disordered states. A significant wavelength shift of the microlaser
is observed, resulting from the dramatic changes in the refractive index of
liquid-crystal microdroplets during the phase transition. This phase-transition
microcavity laser is then exploited for sensitive thermal sensing, enabling
two-order-of-magnitude enhancement in sensitivity compared with the
nematic-phase microlaser operated far from the transition point.
Experimentally, we demonstrate an exceptional sensitivity of -40 nm/K and an
ultrahigh resolution of 320 uK. The phase-transition microcavity laser features
compactness, softness, and tunability, showing great potential for
high-performance sensors, optical modulators, and soft matter photonics.
