Coexistence of temperature-robust band edge lasers and random lasers for high-quality, speckle-free imaging

In this work, we demonstrate that by coupling random lasing with band edge lasing, high-quality, speckle-free imaging can be achieved even in scattering environments. Results show that band edge lasers and random lasers coexist in a single sample based on dye-doped cholesteric liquid crystals. The emission characteristics of both types of lasers are temperature-dependent. By introducing titanium nitride nanoparticles into the dye-doped cholesteric liquid crystals, the wavelength of the band edge lasers becomes temperature-stable. Meanwhile, the variation in emission intensity of the random lasers is reduced with temperature changes, reflecting the inherent randomness of random lasers. Additionally, the random laser exhibits lower temporal coherence, while the band edge laser shows higher spatial coherence, resulting in distinct imaging characteristics. Random laser imaging is inherently speckle-free but suffers from low image contrast, whereas band edge laser imaging offers high contrast at the cost of severe speckle artifacts. Coupling the two types of lasers reduces the speckle and enhances the image quality. Compared to using band edge lasers and random lasers separately, the combined light source improves the signal-to-noise ratio by 2.29 times and 1.69 times, respectively. This work presents a strategy for stable laser imaging with high contrast and speckle-free performance, offering significant potential for applications in speckle-free imaging, bioimaging, and free-space optical communication.