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hardware:scanner [2018/05/21 23:14]
Jon Daniels created |
hardware:scanner [2019/04/16 12:20]
Jon Daniels [Scanner] added screenshot of schematic |
| ====== Scanner ====== | ====== Scanner ====== |
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| The very initial iSPIM and diSPIM in the Shroff lab used a homebuilt scanner system with galvo. ASI developed a "scanner" that uses a MEMS mirror to create a light sheet. Several variants exist including versions with a cylinder lens for fixed sheet, a version based on ASI's C60-CUBE-III which is ideal for phototargeting or TIRF or other applications where it's important to fill the BFP (in contrast with light sheet with low-NA beams), and with an anti-striping option. | The very initial iSPIM and diSPIM in the Shroff lab used a homebuilt scanner system with galvo. ASI developed a compact "scanner" that uses a MEMS mirror to create a light sheet. A patent is pending. Several variants exist including versions with a cylinder lens for fixed sheet, a version based on ASI's C60-CUBE-III which is ideal for phototargeting or TIRF or other applications where it's important to fill the BFP (in contrast with light sheet with low-NA beams), and one with a fancy scan lens for non-light sheet applications where distortions are unacceptable. There is also an anti-striping option. |
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| | Most often a fiber collimator (FC/PC or FC/APC) is used to couple the excitation beam into the scanner, or free-space coupling is possible. The output is C-mount threads that easily attach to an ASI tube lens (i.e. the scan lens is an integral part of the scanner itself). In order to scan the beam exactly parallel to itself 4f spacing needs to be maintained between the MEMS mirror and the sample, meaning that the spacing between the scanner tube lens and objective back focal plane needs to be correct. |
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| | A schematic of the scanner: ({{:hardware:scanner_labeled.pdf|PDF}}). |
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| | {{ :hardware:scanner_schematic.jpg?400 |}} |
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| ===== Cylinder Lens vs. Scanned Beam ===== | ===== Cylinder Lens vs. Scanned Beam ===== |
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| The same scanner body can accommodate a cylindrical lens to make a stationary light sheet. | The light sheet scanner body can accommodate a cylindrical lens to make a stationary light sheet. The external appearance is identical. The same physical microscope can be either a scanned (digital) system or a static sheet system by changing out the scanner. |
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| The advantages of the cylindrical lens version include: | The advantages of the cylindrical lens version include: |
| A good rule of thumb with standard objectives is that both the scan and max flyback can keep up with the camera readout speed but not go too much faster. E.g. with 512 rows the readout time is 2.5ms and we can do a 2.5ms scan and flyback in 2.5ms for 200fps. | A good rule of thumb with standard objectives is that both the scan and max flyback can keep up with the camera readout speed but not go too much faster. E.g. with 512 rows the readout time is 2.5ms and we can do a 2.5ms scan and flyback in 2.5ms for 200fps. |
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| | Larger MEMS mirrors are available and may be useful to achieve higher illumination NA when required. However, the larger mirrors usually have a lower resonance so cannot be driven as fast. |
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| | An arcane optical effect called "bow" that occurs when the axis of rotation isn't orthogonal to the plane made by the incoming/outgoing beams. Since we have a 2D mirror, only one of the rotation axes can be made perpendicular to the beam plane and the other axis unavoidably suffers from this bow problem. The resulting effect is a slight optical coupling of the axes, on the order of a few percent over the entire mirror travel for a standard scanner. The Tiger controller firmware compensates for the effect automatically in internal mode and a per-axis compensation factor can be set (''ERROR'' command). With a cylindrical lens, the "ideal" axis can be either the line axis (allowing you to perfectly smear out the Gaussian intensity profile within the plane) or else the slice axis (allowing you to move the light sheet to create a stack in piezo/slice synchronous scan mode without tilting the light sheet), but not both simultaneously. This has to be set in the factory during scanner assembly, and unless otherwise specified the latter option is chosen, which also corresponds to having the cylindrical lens scanner oriented in exactly the same manner as a Gaussian beam scanner. |
| If you are really interested in FCS and/or pushing the diSPIM speed I suggest a cylindrical lens scanner which generates a static sheet, then no scanning is involved. Besides not worrying about scan/flyback, you can also leave the laser on during camera readout so in that earlier example you can actually do 400fps (the camera limit) instead of 200fps. | |
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