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{1389}
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ref: -0 tags: photoacoustic tomography mouse imaging q-switched laser date: 05-11-2017 05:23 gmt revision:1 [0] [head]

Single-impulse panoramic photoacoustic computed tomography of small-animal whole-body dynamics at high spatiotemporal resolution

  • Used Q-switched Nd:YAG and Ti:Sapphire lasers to illuminate mice axially (from the top, through a diffuser and conical lens), exciting the photoacuostic effect, from which they were able to image at 125um resolution a full slice of the mouse.
    • I'm surprised at their mode of illumination -- how do they eliminate the out-of-plane photoacoustic effect?
  • Images look low contrast, but structures, e.g. cortical vasculature, are visible.
  • Can image at the rep rate of the laser (50 Hz), and thereby record cardiac and pulmonary rhythms.
  • Suggest that the photoacoustic effect can be used to image brain activity, but spatial and temporal resolution are limited.

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ref: -0 tags: photoacoustic tomography mouse imaging q-switched laser date: 05-11-2017 05:21 gmt revision:0 [head]

Single-impulse panoramic photoacoustic computed tomography of small-animal whole-body dynamics at high spatiotemporal resolution

  • Used Q-switched Nd:YAG and Ti:Sapphire lasers to illuminate mice axially, exciting the photoacuostic effect, from which they were able to image at 125um resolution a full slice of the mouse.
  • Images look low contrast, but structures, e.g. cortical vasculature, are visible.
  • Can image at the rep rate of the laser (50 Hz), and thereby record cardiac and pulmonary rhythms.
  • Suggest that the photoacoustic effect can be used to image brain activity, but spatial and temporal resolution are limited.

{1348}
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ref: -0 tags: David Kleinfeld cortical vasculature laser surgery network occlusion flow date: 09-23-2016 06:35 gmt revision:1 [0] [head]

Heller Lecture - Prof. David Kleinfeld

  • Also mentions the use of LIBS + q-switched laser for precisely drilling holes in the scull. Seems to work!
    • Use 20ns delay .. seems like there is still spectral broadening.
    • "Turn neuroscience into an industrial process, not an art form" After doing many surgeries, agreed!
  • Vasodiliation & vasoconstriction is very highly regulated; there is not enough blood to go around.
    • Vessels distant from a energetic / stimulated site will (net) constrict.
  • Vascular network is most entirely closed-loop, and not tree-like at all -- you can occlude one artery, or one capillary, and the network will route around the occlusion.
    • The density of the angio-architecture in the brain is unique in this.
  • Tested micro-occlusions by injecting rose bengal, which releases free radicals on light exposure (532nm, 0.5mw), causing coagulation.
  • "Blood flow on the surface arteriole network is insensitive to single occlusions"
  • Penetrating arterioles and venules are largely stubs -- single unbranching vessels, which again renders some immunity to blockage.
  • However! Occlusion of a penetrating arteriole retards flow within a 400 - 600um cylinder (larger than a cortical column!)
  • Occulsion of many penetrating vessels, unsurprisingly, leads to large swaths of dead cortex, "UBOS" in MRI parlance (unidentified bright objects).
  • Death and depolarizing depression can be effectively prevented by excitotoxicity inhibitors -- MK801 in the slides (NMDA blocker, systemically)

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ref: -0 tags: laser induced breakdown spectroscopy for surgery tissue differentiation date: 09-22-2016 19:26 gmt revision:0 [head]

PMID-25426327 Laser induced breakdown spectroscopy for bone and cartilage differentiation - ex vivo study as a prospect for a laser surgery feedback mechanism.

  • Mehari F1, Rohde M2, Knipfer C2, Kanawade R1, Klämpfl F1, Adler W3, Stelzle F4, Schmidt M1.
  • Tested on pig ear cartilage & cortical bone.
  • 532nm, Q-switched, flashlamp-pumped Nd:YAG, 80mJ pulse energy, 10ns, 1Hz.
  • Commercial spectrogram; light collected with 50um fiber optic connector.
    • We could probably put this in line with the laser mirrors, probably..
  • Super clean results: see any of the figures.
    • AUC = 1.00 !!

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ref: -0 tags: third harmonic generation Nd:YAG pulsed laser date: 08-29-2015 06:44 gmt revision:7 [6] [5] [4] [3] [2] [1] [head]

Problem: have a Q-switched Nd:YAG laser, (flashlamp pumped, passively Q-switched) from ebay (see this album). Allegedly it outputs 1J pulses of 8ns duration; in practice, it may put several 100mJ pulses ~ 16ns long while the flashlamp is firing. It was sold as a tattoo removal machine. However, I'm employing it to drill micro-vias in fine polyimide films.

When focused through a 10x objective via the camera mount of an Leica microscope, 532nm (KTP doubled, second harmonic generation (SHG)) laser pulses both ablates the material, but does not leave a clean, sharp hole: it looks more like 'blasting': the hole is ragged, more like a crater. This may be from excessive 1064nm heating (partial KTP conversion), or plasma/flame heating & expansion due to absorption of the 532nm / 1064nm light. It may also be due to excessive pulse duration (should the laser not actually be q-switched... photodiode testing suggests otherwise, but I'd like to verify that), excessive pulse power, insufficient pulse intensity, or insufficient polyimide absorption at 532nm.

The solution to excessive plasma and insufficient polyimide absorption is to shift the wavelength to 355nm (NUV) via third harmonic generation, 1064 + 532 = 355nm. This requires sum frequency generation (SFG), for which LBO (lithium triborate) or BBO (beta-barium borate) seem the commonly accepted nonlinear optical materials.

To get SHG or THG, phase and polarization matching of the incoming light is critical. The output of the Nd:YAG laser is, I assume, non-polarized (or randomly polarized), as the KTP crystal simply screws on the front, and so should be rotationally agnostic (and there are no polarizing elements in the simple laser head -- unless the (presumed) Cr:YAG passive Q-switch induces some polarization.)

Output polarization of the KTP crystal will be perpendicular to the incoming beam; if the resulting THG / SFG crystal needs Type-1 phase matching (both in phase and parallel polarization), will need a half-wave plate for 1064nm; for Type-II phase matching, no plate is needed. For noncritical phase matching in LBO (which I just bought), an oven is required to heat the crystal to the correct temperature.

This suggests 73C for THG, while this suggests 150C (for SHG?).

Third harmonic frequency generation by type-I critically phase-matched LiB3O5 crystal by means of optically active quartz crystal Suggests most lasers operate in Type-1 SHG, and Type-II THG, but this is less efficient than dual Type-1; the quartz crystal is employed to rotate the polarizations to alignment. Both SHG and THG crystals are heated for optimum power output.

Finally, Short pulse duration of an extracavity sum-frequency mixing with an LiB3O5 (LBO) crystal suggests that no polarization change is required, nor oven control LBO temperature. Tight focus and high energy density is required, of course (at the expense of reduced crystal lifetime). Likely this is the Type-1,Type-II scheme alluded to in the paper above. I'll try this first before engaging further complexity (efficiency is not very important, as the holes are very small & material removal may be slow.)

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ref: -0 tags: spectroscopy frequency domain PMT avalanche diode laser Tufts date: 02-25-2014 19:02 gmt revision:0 [head]

Frequency-domain techniques for tissue spectroscopy and imaging

  • 52 pages, book chapter
  • Good detail on bandwidth, tissue absorption, various technologies.

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ref: Song-2009.08 tags: wireless neural recording RF Brown laser optical Donoghue date: 01-15-2012 00:58 gmt revision:6 [5] [4] [3] [2] [1] [0] [head]

IEEE-5067358 (pdf) Wireless, Ultra Low Power, Broadband Neural Recording Microsystem

  • 16 channels.
  • Use a VCSEL (vertical cavity surface emission laser) to transmit data through the skin.
  • Nice design, and they claim to have made recordings for 1 month already.
  • One PCB, kapton substrate reinforced with alumina where needed.
  • Custom 12mW neural amplifier.

____References____

Song, Y.-K. and Borton, D.A. and Park, S. and Patterson, W.R. and Bull, C.W. and Laiwalla, F. and Mislow, J. and Simeral, J.D. and Donoghue, J.P. and Nurmikko, A.V. Active Microelectronic Neurosensor Arrays for Implantable Brain Communication Interfaces Neural Systems and Rehabilitation Engineering, IEEE Transactions on 17 4 339 -345 (2009)

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ref: engineering notes-0 tags: BGA PCB design blueCore bluetooth laser drilling CSR via clearance date: 03-19-2008 22:35 gmt revision:4 [3] [2] [1] [0] [head]

This is from the CSR reference design for the BlueCore5 chip.

They also note that you have to pay attention to the aspect ratio of the vias - with laser drilling, this means that they needed a 63um prepreg between layers 1 and 2 (ground), with start copper thickness of 18um.

PTH = plated-through-hole. (refers to a type of via)

For 0.8mm BGA, you can loosen the design rules to the following: "

Minimum track width0.125mm(*) local, 0.15mm global0.005"
Minimum clearance0.125mm(*)0.005"
Minimum thru-hole0.15mm hole, 0.4mm landing under BGA0.006" on 0.016"
0.25mm hole, 0.6mm landing global0.01" on 0.024"
Solder Mask opening0.075mm radius opening around pads0.003"
(*) note: For a 0.8mm BGA with 0.4mm diameter pads, this could technically be 0.133mm, but I prefer to round to 1/8mm or just about 0.005"

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ref: -0 tags: laser power concentration GFP mCherry calibration date: 02-01-2008 19:22 gmt revision:0 [head]

above, a set of curves for determining fluorescent protein concentration (GFP & mCherry) from received photon count in a two-photon microscope. Unfortunately, these depend on efficiency & power of the entire setup, so the curve is non-transferable to other microscopes.

one pass of mCherry @ 5x dilution did not seem the same as the others -- perhaps the reading light was left on?

% given a series of files, 
% calculate a quadratic to convert intensity to concentration. 
% assumed formula: 
% green intensity = background + const*[GFP]*laserpower^2
% red intensity = background + const*[RFP]*laserpower^2 +
%               const2[GFP]*laserpower^2
close all
cd('/var/ftp/tim_hanson/T002-0130_08/solutions'); 
basename = 'T002-gfp-100xdil-'; 
int_gfp100 = IntensReadfile('T002-gfp-100xdil-', 11, 2); 
int_gfp10 = IntensReadfile('T002-gfp-10xdil-', 8, 2);
int_mcherry10 = IntensReadfile('T002-mcherry-10xdil-', 7, 2);
int_mcherry5 = IntensReadfile('T002-mcherry-5xdil-', 7, 2);
int_mcherry5_2 = IntensReadfile('T002-mcherry-5xdil2-', 7, 2);
int_mcherry5_4 = IntensReadfile('T002-mcherry-5xdil4-', 6, 2);

bg_green = (int_gfp100(1) + int_gfp10(1))/2;
bg_red = (int_mcherry10(1) + int_mcherry5(1)...
    + int_mcherry5_2(1) + int_mcherry5_4(1))/4; 
powers = (0:0.1:1).^2;
int_gfp_all = [int_gfp100-bg_green, (int_gfp10-bg_green)/10]; 
pow_gfp_all = [powers(1:11), powers(1:8)]; 
green_intensity_perpower = pow_gfp_all'\int_gfp_all'
green_lab = ['green intensity = ' num2str(green_intensity_perpower) ' * power^2 + ' ...
    num2str(bg_green) ' (photons/10us) @ 8.7 ug/ml conc. gfp']; 

figure
plot(sqrt(powers(1:11)), int_gfp100, 'o'); 
hold on
plot(sqrt(powers(1:8)), (int_gfp10-bg_green)/10+bg_green, 'or'); 
plot(sqrt(pow_gfp_all), pow_gfp_all * green_intensity_perpower + bg_green, 'gx'); 
legend('100x dilution','10x dilution','parabolic fit'); 
title('intensity of gfp vs. laser power normalized to 100x dilution')
xlabel(green_lab); 

int_mch_all = [(int_mcherry10-bg_red)/10, (int_mcherry5-bg_red)/20, ...
    (int_mcherry5_2-bg_red)/20, (int_mcherry5_4-bg_red)/20]; 
pow_mch_all = [powers(1:7), powers(1:7), powers(1:6), powers(1:7)]; 
red_intensity_perpower = pow_mch_all'\int_mch_all'
red_lab = ['red intensity = ' num2str(red_intensity_perpower) ' * power^2 + ' ...
    num2str(bg_red) ' (photons/10us) @ 8.7 ug/ml conc. mcherry']; 

figure
plot(sqrt(powers(1:7)), (int_mcherry10-bg_red)/10+bg_red, 'o'); 
hold on
plot(sqrt(powers(1:7)), (int_mcherry5-bg_red)/20+bg_red, 'or'); 
plot(sqrt(powers(1:7)), (int_mcherry5_2-bg_red)/20+bg_red, 'ok'); 
plot(sqrt(powers(1:6)), (int_mcherry5_4-bg_red)/20+bg_red, 'om');
plot(sqrt(pow_mch_all), pow_mch_all * red_intensity_perpower + bg_red, 'gx'); 
legend('10x dilution','5x dilution','5x dilution(2)','5x dilution(4)','parabolic fit'); 
title('intensity of mcherry vs. laser power normalized to 100x dilution')
xlabel(red_lab)

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ref: notes-0 tags: two-photon laser imaging fluorescence lifetime imaging FRET GFP RFP date: 01-21-2008 17:23 gmt revision:0 [head]

images/538_1.pdf