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1)Adaptive optics: optimization and wavefront sensing 2)Novel microscope enhancements
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widefield confocal
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Spherical Aberration (on axis) Perfect lens Real lens 2 related types, lateral and transverse Different effective focal lengths, positions Constant optical Path difference Every ray arrives At same focal point
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Adaptive optics idea Active element undoes what microscope, specimen does to PSF Correction is determined by iteration: genetic algorithms, random searches More correction takes more time
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37 element micromachined deformable mirror Can travel 6 microns
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Norris. J. Microcopy 2002 Performance for TPEF of coumarin dye solution Good agreement with calculated, measured in simple specimen
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Adaptive optics on non-scanning 2-photon microscope 600 microns into solution: PSF greatly improved
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Lateral PSFs (measured by THG) Adaptive optics improves resolution and signal strength For nonlinear optical processes (TPEF, SHG, THG, CARS)
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Girkin, OPEX Optimize feedback based on two-photon fluorescence intensity Setup for adaptive optics on laser scanning microscope
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Correction for TPEF of sub-resolution bead x-y optical section Significant improvement even for beads in water
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Correction for TPEF of sub-resolution bead x-z cross section Significant improvement even for beads into 30 microns of water
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Improvement in PSF important for multiphoton processes
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TPEF of guinea pig bladder 1.3 NA 40x 30 microns into the tissue Surface optimized Optimized for 30 microns Need to optimize at every depth
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CARS and adaptive optics Xie and Girkin Opex
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Non-resonant CARS from glass-air interface
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Depth dependence of CARS for beads in agarose Optimizing at greatest depth works best Systems aberrations also very important
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Comparison of CARS image with system, sample induced aberrations 600 microns into solution
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Comparison of CARS image with system, sample induced aberrations from tissue
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Radial Dependence of correction Best response when optimize at every point But very slow
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Adaptive Optics by Wavefront correction Denk, PNAS, 2006
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Astigmatism Different planes Have different Focal lengths
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Correction of Astigmatism
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AO on zebrafish larvae Olfactory bulb:GFP 50 microns 200 microns Imaging bloodflow
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Wavefront sensing and correction using Spatial Light Modulator SLM larger range than Deformable mirror: better depth Eliceiri tbp
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MPE in vivo live animal imaging Flexible periscope converts inverted to upright microscope
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Difficulties with live animal imaging: respiration 8 second intervals, each scan 2 seconds Few micron motion, even anesthetized
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Performance for in vivo imaging of muscle
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Imaging through 200 microns of tissue
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TPEF of kidney of anesthetized rabbit kidney Breath-holding for one minute: Necessary for internal organ imaging
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Fraction of light collected in epi-illumination geometry High NA only collects 30% of available light (ideal limit without absorption and scattering)
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Parabolic reflector to enhance light collection Balaban, J. Microscopy (2007)
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Light Attenuation in tissue Z= depth from surface Simplest case fit to µ s [cm -1 ] 1/ µ s =scattering length, or mean free path Multiple scattering in thick, turbid media g=anisotropy, avg cos 0=isotropic 1=all forward Tendon~0.9 Brain=0.1
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Photon Transport Theory J(r,s) in a specific direction s within a unit solid angle dω Anisotropy around propagation axis radiance J(r,s) relates to the observable quantity, intensity I through the relation
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Absorption weakens intensity Scattering changes direction Calculate photon weight by albedo New direction based on g Continue until photon escapes Forward or backwards Monte Carlo Simulation of Irradiance: Based on probabilities from optical parameters
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Calculation of enhancements based On Monte Carlo simulation Muscle more absorbing than brain: limits enhancement Over purely scattering tissues
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Comparison of gain in simulation and experiment for beads in phantom using optical parameters in literature Gain over epi-detection is substantial
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GasiGasi Gain is ~8 fold Predicted ~12 fold Discrepancy probably due to imperfect optics
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