Interferometric Focusing of Excitation Light onto a Guide-Star

Optical microscopy allows noninvasive imaging of biological tissues at a sub cellular level. However, the optimal performance of the microscope is hard to achieve because of aberrations induced from tissues. The shallow penetration depth and degraded resolution provide a limited degree of information for biologists. In order to compensate for aberrations, adaptive optics with direct wave front sensing, where guide-stars are used for wave front measurement, has been applied in microscopy. The scattering effect limits the intensity of a guide-star and hence reduces the signal to noise ratio of the wave front measurement. In this paper, we propose to use interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescence intensity, thus overcoming the signal loss caused by scattering. With interferometric focusing of light, we increase the signal to noise ratio of the laser guide-star through scattering tissue by more than two times as well as potentially extending the thickness of tissue that can be corrected using AO microscopy.