We have an Andor iccd which is coupled with a pulse laser for TRPL measurements. The software provided with the system asks the user to specify delay time (with respect to laser pulse), TTL width, gate width, exposure, and gain for kinetic mode. I understand that once photons hit the photocathode, intensifying tube in these system amplify electrons by MCP, which are collected by the phosphor plate coupled to ccd. If I am right the ccd in the camera is ON for "exposure" time. Gate width is the time for which intensifier is ON. What then is the TTL width for? Thanks!
I am not quite sure to answer your question correctly. During my PhD I als stumbled over these technical parameters. A colleague visualised the TTL (transistor transistor logic) signal from a laser diode controller in my context with a oscilloscope visualising that the electronic signal provided is a short voltage peak with a width (time) and amplitude in Volts. Normally it should be 5V, but it can be also distinctly less which can influence the device that needs to read the signal. In your case it could be the broadness in time of this electronic pulse.
My signal was a 10-80MHz pulsed diode and thus for 10MHz we measured a TTL peak of about 3-3.5V every 100ns with a width distinclty shorter (~ns, I forgot...it was 10 years ago.)
I have a bit experience with synchronizing laser shutter with Andor CCD camera, where the shutter takes the timing out port from the CCD camera as input, which gives also TTL pulse (it is explained in Andor Manuals which outgoing port of the CCD gives which kind of signal) e.g. in 100ms binning time, you often have ~98ms exposure and some ~2ms readout, at that this point the signal drops from 5V to 0 and rises again. This short TTL drop can be converted by a JK flipflop to change the state of the laser shutter between on and off and vice versa. The shutter for example also use a 5V (permanant) signal to remain in either state. In our case the TTL width of the shutter would be as long as the exposer time. The principle is found in Article Single-Molecule Three-Color FRET with Both Negligible Spectr...
(Figure 4).To tell you which width you need, it is probably necessary to know more details about your setup and you pulse time window. I hope this helps a little.
Thank you for elaborate answer, Dr. Kowerko.
We have a 1000Hz repetition rate pulsed laser, which would mean a TTL pulse every 1ms with certain width. We change the TTL width (2ns to few micro sec) depending on which region of luminescence delay (after laser pulse) is being measured. The laser pulse has width ~ 850ps-1ns. Since you mentioned shutter on-off is related to TTL drop, it would mean that TTL width of 2ns is the duration for which the shutter is open. (Although I am not sure if 2ns is also the readout time.) So TTL width is a short time for which data is collected (although exposure minimum is few 100 micro sec!).
For our system, width of shutter (TTL) is generally very small compared to exposure time. I believe this may have to do with type of camera we have (intensifier ccd) versus the EM-CCD mentioned in the Article Single-Molecule FRET.
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