I am using Quantel brilliant ND:YAG laser. I want to trigger my spectrometer using a delay generator for laser induced breakdown spectroscopy. Spectrometer is ocean optics usb 4000. Can anybody explain me the simple way for it?
Hi there,
Without looking at the detailed specs of your laser and spectrometer I can't give you an exact answer. One way would be to synchronize both your laser and your spectrometer with a separate pulse from your delay generator. Probably your laser will be able to accept a trigger input that determines the time delay between the flash light and the the Q-switch, the laser pulse exiting the cavity at the end of the trigger pulse. If not, your laser may have an output that sends a signal just before each pulse, which you can use as a sync input to your delay generator. You then need to set up a waveform that will trigger your spectrometer to capture a frame; the spectrometer will have a sync input for that. Presumably the laser pulse will be so much shorter than the shortest integration time you can achieve with the spectrometer that in order to get the timing right you could start capturing before firing the pulse. But this is just me guessing. Ah - before I forget - your spectrometer may actually have a sync OUTPUT that can be used to trigger your laser. Some spectrometers provide such an output especially for breakdown or fluorescence spectroscopy. Anyway, the manuals will tell you. Hope this is of some help. If I've forgotten something I'm sure someone will add it...:P.
Good luck,
Marco
Hello guy,
I've worked with the sync between laser and other instruments and one difficulty found is that laser quality including timing jitter is not good if laser is in single-shot operation mode. It is obvious that laser is in stationary when being operated with the normal repetition rate. (Usually higher repetition rate is good in terms of stability.)
Thus I introduced a little bit of complicated setup. I added electronics called 'single-shot controller' in my term. The photodiode hit by the fraction of the laser connnected to the controller and the controller has external trigger like button. When the button is touched, the controller selected one photodiode signal just next when triggered and that signal plays the master signal. The master signal sent to delay generator to sync all necessary instruments.
In this kind of setup, timing jitter is really comparable or less than 1 ns.
Oh I got some interesting product like http://www.conoptics.com/pulse-selection-systems/
It looks there is already (absolutely expected as there are a lot of demand of instrument sync) commercialized laser-sync electronics.
Marco gives good advice. You can probably find used delay generators, like the Tektronix 500 series, for pennies on the dollar on eBay. A very much cheaper option is to construct circuits based on 74121 or 74124 TTL chips. I have a drawer full of these and in a pinch, can throw together a variable delay in an hour or so.
You can trigger USB 4000 - check the manual at ww.oceanoptics.com - it has an input at port #7 (if I remeber correctly, maybe 5) - you need only to supply a TTL signal. There are two major problems here: first there is a delay of ~ 7ms (my case) between acquring a TTL signal and recording the spectrum by USB4000 - this means laser pulse is already gone when you measure the spectrum. To avoid that - use a trigger delay line that will generate control pulse BEFORE the laser pulses for the second time. Second, this particular system is rather strange and when it is triggered it has LOWER sensitivty compared to a normal run (without triggering) at the same exposure. I wrote a LABVIEW software that records all the spectra from this system in the normal run (nontriggered); thus, I end up having several empty spectra between pulses and some spectra that were acquired in time to record the laser pulse.
Good luck!
If you decide to construct your own circuit, you will need a data sheet. The data sheet for the 74121 can be found in the link. You also want to look for a TTL "cookbook" to help you plan the circuit. There should be one in your library if you have an electrical engineering school at your university.
You need to be aware that things are not triggered on pulses as much as they are on edges. The subtle difference is that a pulse has a rising and a falling edge. Simple devices trigger on falling edges but I have used others that are positive edge triggered. Depending on which is the business edge for you laser and spectrometer, you might have to invert the signal.
As a general rule, it is better to drive instruments using what is called and open collector output. The 74121 is not open collector but one can find buffers and inverters that are. The advantage in open collector circuits is that impedence matching is easier amd you will not blow out the 74121 with reflected pulse, or more common, a shift in ground potential imposed by the laser in particular.
I almost forgot to mention that there are few books that may describe these circuits. The basics book is Malmstadt, Enke and Crouch "Electroics and Instrumentation for Scientists". A more detailed book is Horowitz and Hill, "The Art of Electronics"
http://www.ti.com/lit/ds/symlink/sn74121.pdf
Depends on the laser system you are using. One way is use your flash lamp output to trigger the delay generator, then apply the required (based on laser spec and energy requirement) the delay to the Q-switch input of the laser, apply the required delay to the spectrometer as well. In this case your Flash lamp output is the reference. Another method is, if you already know the Flash lamp-Q-switch delay in your laser system take the flash lamp trigger out give it as a trigger to delay generator apply the delay to the spectrometer (Here laser is triggered internally in the previous method triggered externally). Keep in mind that your Ocean optics spectrometer may have an inbuilt delay.
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