Surface-emitting semiconductor laser for intracavity spectroscopy and microscopy

The authors demonstrate lasing action in a novel microcavity laser which can be utilized for intracavity spectroscopy as well as high contrast imaging of small ({approximately} 10{mu}m) structures. The system can be easily visualized as a Fabry-Perot cavity containing a gain media and an object for study. Since the primary constraint on the object is transparency at the lasing wavelength, investigation of lasing in objects such as microspheres, liquid droplets, and biological cells is possible. The resonator consists of an epitaxial NME grown mirror and gain region on a GaAs wafer. This is essentially an open-cavity vertical cavity surface emitting laser (VCSEL). The object to be studied is placed on the wafer and covered with a glass dielectric mirror which acts as the output coupler. When the semiconductor gain region is photo-pumped, the object within the cavity provides lateral optical confinement through its index difference with the surrounding media, increases the cavity Q, and thus encourages lasing action. The emitted laser light can be spectrally and spatially resolved. The narrow lasing lines can provide information about the lasing modes supported and the size of the object. The spatially resolved laser light provides high contrast microscopic images of the electromagnetic modes oscillating in the resonator. The authors present an investigation of stable lasing modes in polystyrene spheres. This device could prove useful in biomedical diagnostics. It covers the correct spatial dimensions as well as wavelength region. In fact, an integrated system of these devices may provide a high speed, compact method of performing cell diagnostics