Shack-Hartmann wavefront sensing using interferometric focusing of light onto guide-stars

Abstract

Optical microscopy provides noninvasive imaging of biological tissues at subcellular level. The optical aberrations induced by the inhomogeneous refractive index of biological samples limits the resolution and can decrease the penetration depth. To compensate refractive aberrations, adaptive optics with Shack-Hartmann wavefront sensing has been used in microscopes. Wavefront measurement requires light from a guide-star inside of the sample. The scattering effect limits the intensity of the guide-star, hence reducing the signal to noise ratio of the wavefront measurement. In this paper, we demonstrate the use of interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescent intensity, thus overcoming the excitation signal loss caused by scattering. With interferometric focusing, we more than doubled the signal to noise ratio of the laser guide-star through scattering tissue as well as potentially extend the imaging depth through using AO microscopy.

Ultrathin endoscopes based on multicore fibers and adaptive optics: a status review and perspectives

“…16 At the present state, it seems that aberrations incurred by ballistic photons can be well corrected by adaptive optics. 17,18 However, it is much less clear whether adaptive optics is capable of recovering more than just a small fraction of scattered photons. [19][20][21][22] So, adaptive optics may well also be limited by the depletion of ballistic photons.…”

In vivo volumetric imaging of biological dynamics in deep tissue via wavefront engineering

“…Adaptive optics has been applied to microscopy to compensate wavefront distortion for deep tissue imaging [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Multiple methods of wavefront measurement and compensation have been successfully demonstrated, such as direct wavefront sensing with a wavefront sensor [20] or a low coherence interferometer [21], feedback-based modal wavefront sensing [22] and pupilsegmentation based adaptive optics [23], etc. We have developed the iterative multiphoton adaptive compensation technique (IMPACT) [24], and demonstrated its capability in imaging through highly scattering tissue, such as the intact mouse skull [25,26].…”

Deep Tissue Wavefront Estimation for Sensorless Aberration Correction

“…Overcoming these challenges will benefit a wide range of applications from basic biological research to clinical investigations. Although scattering will exponentially reduce the intensity of ballistic light with the imaging increasing depth, correction of refractive aberration still benefits the imaging resolution and contrast [1,2]. Wavefront correction can dramatically reduce the surrounding lobes of the point spread function.…”

“…When using Shack-Hartmann wavefront sensing, the scattering will not only limit the amount of photons delivered to the guide-star, but also increase the background noise. In a recent study, near IR guide star has been used for a two photon microscope to extend the wavefront measurement depth [2]. Interferometric focusing has been also applied to a guide star to increase the SNR of the wavefront sensor [1].…”