m8ta
You are not authenticated, login.
text: sort by
tags: modified
type: chronology
{1555}
hide / / print
ref: -0 tags: adaptive optics two photon microscopy date: 10-26-2021 18:17 gmt revision:1 [0] [head]

Recently I've been underwhelmed by the performance of adaptive optics (AO) for imaging head-fixed cranial-window mice. There hasn't been much of an improvement, despite significant optimization effort. This begs the question: where are AO microscopes used?

When the purpose of a paper is to explain and qualify an novel AO approach, the improvement is always good, >> 2x. Yet, in the one paper (first below) when the purpose was neuroscience, not optics, the results are less inspiring. Are the results from the optics papers cherry-picked?

Thalamus provides layer 4 of primary visual cortex with orientation- and direction-tuned inputs Wenzhi Sun, Zhongchao Tan, Brett D Mensh & Na Ji 2016 https://www.nature.com/articles/nn.4196

  • This is the primary (only?) paper where AO was used, but the focus was biology: measuring the tuning properties of thalamic boutons in mouse visual cortex. Which they did, well!
  • Surprisingly, the largest improvement was not from using AO, but rather from thinning the cranial window from 340um to 170um.
  • "With a 340-μm-thick cranial window, 70% of all boutons appeared to be non-responsive to visual stimuli and only 7% satisfied OS criteria. With a thinner cranial window of 170-μm thickness, we found that 31% of boutons satisfied OS criteria (of total n = 1,302, 5 mice), which was still substantially fewer than 48% OS boutons as determined when the same boutons (n = 1,477, 5 mice) were imaged after aberration correction by adaptive optics"

Direct wavefront sensing for high-resolution in vivo imaging in scattering tissue Kai Wang, Wenzhi Sun, Christopher T. Richie, Brandon K. Harvey, Eric Betzig & Na Ji, 2015 https://www.nature.com/articles/ncomms8276

  • Direct wavefront sensing using indocayanine green + Andor iXon 897 EMCCD Shack-Hartmann wavefront sensor (read: expensive).
  • Alpao DM97-15, basically the same as ours.
  • Fairly local wavefront corrections, see figure 2.
  • Also note that these wavefront corrections seem low-order, hence should be correctable via a DM

Multiplexed aberration measurement for deep tissue imaging in vivo Chen Wang, Rui Liu, Daniel E Milkie, Wenzhi Sun, Zhongchao Tan, Aaron Kerlin, Tsai-Wen Chen, Douglas S Kim & Na Ji 2014 https://www.nature.com/articles/nmeth.3068

  • Use a DMD (including a dispersion pre-compensator) to amplitude modulate phase ramps on a wavefront-modulating SLM. Each phase-ramp segment of the SLM was modulated at a different frequency, allowing for the optimal phase to be pulled out later through a Fourier transform.
  • Again, very good performance at depth in the mouse brain.

{1487}
hide / / print
ref: -0 tags: adaptive optics sensorless retina fluorescence imaging optimization zernicke polynomials date: 11-15-2019 02:51 gmt revision:0 [head]

PMID-26819812 Wavefront sensorless adaptive optics fluorescence biomicroscope for in vivo retinal imaging in mice

  • Idea: use backscattered and fluorescence light to optimize the confocal image through imperfect optics ... and the lens of the mouse eye.
    • Optimization was based on hill-climbing / line search of each Zernicke polynomial term for the deformable mirror. (The mirror had to be characterized beforehand, naturally).
    • No guidestar was needed!
  • Were able to resolve the dendritic processes of EGFP labeled Thy1 ganglion cells and Cx3 glia.

{1418}
hide / / print
ref: -0 tags: nanophotonics interferometry neural network mach zehnder interferometer optics date: 06-13-2019 21:55 gmt revision:3 [2] [1] [0] [head]

Deep Learning with Coherent Nanophotonic Circuits

  • Used a series of Mach-Zehnder interferometers with thermoelectric phase-shift elements to realize the unitary component of individual layer weight-matrix computation.
    • Weight matrix was decomposed via SVD into UV*, which formed the unitary matrix (4x4, Special unitary 4 group, SU(4)), as well as Σ\Sigma diagonal matrix via amplitude modulators. See figure above / original paper.
    • Note that interfereometric matrix multiplication can (theoretically) be zero energy with an optical system (modulo loss).
      • In practice, you need to run the phase-moduator heaters.
  • Nonlinearity was implemented electronically after the photodetector (e.g. they had only one photonic circuit; to get multiple layers, fed activations repeatedly through it. This was a demonstration!)
  • Fed network FFT'd / banded recordings of consonants through the network to get near-simulated vowel recognition.
    • Claim that noise was from imperfect phase setting in the MZI + lower resolution photodiode read-out.
  • They note that the network can more easily (??) be trained via the finite difference algorithm (e.g. test out an incremental change per weight / parameter) since running the network forward is so (relatively) low-energy and fast.
    • Well, that's not totally true -- you need to update multiple weights at once in a large / deep network to descend any high-dimensional valleys.

{90}
hide / / print
ref: bookmark-0 tags: mirror reflective projection lens design NEC optics date: 0-0-2006 0:0 revision:0 [head]

http://www.nec.co.jp/techrep/en/journal/g06/n03/060319.html

very neat - and I'm surprised that they put all of this on the web! you can almost make one of these yourself with the information within.