Re: pre-chirping (what diagnostics to use)
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Shalin Mehta |
Re: pre-chirping (what diagnostics to use)
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Dear Jerry and others,
What diagnostics do you use for tuning of two photon laser or OPO? Is laser spectrum analyzer enough? We have a shared two photon (MIRA 900F Femtosecond configuration) and OPO from Coherent. One of the main user is very afraid of tuning it - so he always has a service engineer tune it to 830nm and longest possible pulse (since he does spectroscopy). There are two more of us who will benefit by tuning it for two-photon and SHG (different wavelengths and shortest possible pulse). How is the 'reproducibility' of laser beam profile when working with these lasers? One of the main concern that other user has is that - if you cannot come back to exactly 830 nm after tuning to say 740 nm, the custom optical setup will go out of alignment. Thanks Regards Shalin On 8/30/07, Mark Cannell <[hidden email]> wrote:
Search the CONFOCAL archive at -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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Mark Cannell |
Re: pre-chirping (what diagnostics to use)
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http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Hi Shalin The spectrum analyser is a must have instrument that will fill most of your needs. You will be able to to tune to the desired wavelength and bandwidth quite easily. Cheers Mark Shalin Mehta wrote: > Search the CONFOCAL archive at > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Dear Jerry and > others, > > What diagnostics do you use for tuning of two photon laser or OPO? Is > laser spectrum analyzer enough? > > We have a shared two photon (MIRA 900F Femtosecond configuration) and > OPO from Coherent. One of the main user is very afraid of tuning it - > so he always has a service engineer tune it to 830nm and longest > possible pulse (since he does spectroscopy). There are two more of us > who will benefit by tuning it for two-photon and SHG (different > wavelengths and shortest possible pulse). > How is the 'reproducibility' of laser beam profile when working with > these lasers? One of the main concern that other user has is that - if > you cannot come back to exactly 830 nm after tuning to say 740 nm, the > custom optical setup will go out of alignment. > > Thanks > Regards > Shalin > > > > On 8/30/07, *Mark Cannell* <[hidden email] > <mailto:[hidden email]>> wrote: > > Search the CONFOCAL archive at > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal > > Hi Gerry > > The typical path using 2 prisms is via a small mirror into the first > prism (we set this at minimum at minimum deviation but this can be > changed to alter chirp). Then to the second prism (at minimum devation > to produce a collimated horizontally spread spectrum), and then two > mirrors to reflect the light back and displace the beam vertically > which > then passes back through the second and first prisms respectively. > After > the beam has left the first prism, note the beam has been displaced > vertically is and thereby separated from the input beam. > > BUT are you sure you need to do this? If the input pulse is ~120 > fs the > pulse broadening is quite minor. We used a pair of gold mirrors to to > return and displace the beam but if you have 1" fs mirrors they would > work as well. > > For typical prism spacing see: > > Soeller, C. & Cannell, M.B. (1996) Construction of a two-photon > microscope and optimisation of illumination pulse width. _Pflugers > Archiv_ 432: 555-561. > > Cheers Mark > > Jerry Sedgewick wrote: > > Search the CONFOCAL archive at > > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal > > > > I am interested in setting up pre-chirping in the laser path > going to > > a custom built multiphoton. I have been searching in vain for exact > > information on the components. I bought the prisms, but I am > uncertain > > about the first mirror that directs the laser to the prisms (and > then > > allows the returning, reflected laser to pass through), and the > second > > mirror. My guess is that the first mirror must be a linear > polarizer, > > or a polarizer that separates the s and p polarization. The second > > mirror must be a grating of some sort that re-polarizes the laser so > > that it passes through the first mirror. > > > > Rather than guessing, it would make my day if I could get > specifics on > > the mirrors. > > > > Thanks! > > > > Jerry Sedgewick > > > > > -- > My co-ordinates: > Shalin Mehta, Graduate student > Graduate Programme in Bioengineering, NUS, Singapore > Email: shalin {dot} mehta {at} gmail {dot} com > Blog: electricsbm.blogspot.com <http://electricsbm.blogspot.com> > Mobile: +65 90694182 |
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In reply to this post by Shalin Mehta
Search the CONFOCAL archive at
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Shalin
wrote; What diagnostics do you use for tuning of two photon laser or
OPO? Is laser spectrum analyzer enough?
The laser spectrum analyser should get you back exactly to your
wavelength, and give a pretty good idea of the pulse length.
Lastek in Australia make a software system which works with a
spectrum analyser to give you pulse length and it seems pretty
good provided it is carefully calibrated. (It's probably sold
under
some other name in the States).
But if you have users who want to know the pulse length
precisely
it's really worthwhile buying an autocorrelator.
We have a shared two photon (MIRA 900F Femtosecond configuration) and OPO from Coherent. One of the main user is very afraid of tuning it - so he always has a service engineer tune it to 830nm and longest possible pulse (since he does spectroscopy). There are two more of us who will benefit by tuning it for two-photon and SHG (different wavelengths and shortest possible pulse). 830 is quite OK for SHG (brings the harmonic to 415 which is within
the range of conventional interference filters (they start to
absorb a lot
at anythong shorter). But it's a bit limiting for 2P.
How is the 'reproducibility' of laser beam profile when working with these lasers? One of the main concern that other user has is that - if you cannot come back to exactly 830 nm after tuning to say 740 nm, the custom optical setup will go out of alignment. In the early days one make of Ti-S laser was notorious for
beam
wander as you tuned it but even so it should go back when you
returned it to the original wavelength. Nowadays they seem
really
stable, and I don't think your Mira should be a problem
there. The
only thing I find with a Mira is that it's best to let it
warm up for
half an hour before doing any tweaking of the alignments (and
often
that way you find you didn't really need to do any tweaking
anyway).
Guy
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Sudipta Maiti |
Re: pre-chirping (what diagnostics to use)
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In reply to this post by Shalin Mehta
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http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Tuning is fairly easy with the MIRA, and reproducibility should be no problem. If you have a spectrometer and an autocorrelator, you can guarantee virtually the same pulse that you had before. For the pulsewidth at a given wavelength, all that should matter is the amount of prism glass you put in the beam (generally less for longer pulses) and the slit width (assuming that the prism angles are set correct and you do not want to play with those). Sudipta On Thu, 30 Aug 2007, Shalin Mehta wrote: > Search the CONFOCAL archive at > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal > > Dear Jerry and others, > > What diagnostics do you use for tuning of two photon laser or OPO? Is laser > spectrum analyzer enough? > > We have a shared two photon (MIRA 900F Femtosecond configuration) and OPO > from Coherent. One of the main user is very afraid of tuning it - so he > always has a service engineer tune it to 830nm and longest possible pulse > (since he does spectroscopy). There are two more of us who will benefit by > tuning it for two-photon and SHG (different wavelengths and shortest > possible pulse). > How is the 'reproducibility' of laser beam profile when working with these > lasers? One of the main concern that other user has is that - if you cannot > come back to exactly 830 nm after tuning to say 740 nm, the custom optical > setup will go out of alignment. > > Thanks > Regards > Shalin > > > > On 8/30/07, Mark Cannell <[hidden email]> wrote: >> >> Search the CONFOCAL archive at >> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal >> >> Hi Gerry >> >> The typical path using 2 prisms is via a small mirror into the first >> prism (we set this at minimum at minimum deviation but this can be >> changed to alter chirp). Then to the second prism (at minimum devation >> to produce a collimated horizontally spread spectrum), and then two >> mirrors to reflect the light back and displace the beam vertically which >> then passes back through the second and first prisms respectively. After >> the beam has left the first prism, note the beam has been displaced >> vertically is and thereby separated from the input beam. >> >> BUT are you sure you need to do this? If the input pulse is ~120 fs the >> pulse broadening is quite minor. We used a pair of gold mirrors to to >> return and displace the beam but if you have 1" fs mirrors they would >> work as well. >> >> For typical prism spacing see: >> >> Soeller, C. & Cannell, M.B. (1996) Construction of a two-photon >> microscope and optimisation of illumination pulse width. _Pflugers >> Archiv_ 432: 555-561. >> >> Cheers Mark >> >> Jerry Sedgewick wrote: >>> Search the CONFOCAL archive at >>> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal >>> >>> I am interested in setting up pre-chirping in the laser path going to >>> a custom built multiphoton. I have been searching in vain for exact >>> information on the components. I bought the prisms, but I am uncertain >>> about the first mirror that directs the laser to the prisms (and then >>> allows the returning, reflected laser to pass through), and the second >>> mirror. My guess is that the first mirror must be a linear polarizer, >>> or a polarizer that separates the s and p polarization. The second >>> mirror must be a grating of some sort that re-polarizes the laser so >>> that it passes through the first mirror. >>> >>> Rather than guessing, it would make my day if I could get specifics on >>> the mirrors. >>> >>> Thanks! >>> >>> Jerry Sedgewick >> > > > > -- Sudipta Maiti Dept. of Chemical Sciences Tata Institute of Fundamental Research Homi Bhabha Road, Colaba, Mumbai 400005, India 91-22-2278-2716 www.tifr.res.in/~biophotonics |
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In reply to this post by Guy Cox
Search the CONFOCAL archive at
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Thanks all for reply.
Given that we provide 1/2 hour for laser to settle is it reasonable to expect that one can tune the laser thrice a day for different users and still it works fine? Autocorrelator is too costly for time being but we do have a spectrum analyzer. Upto now, the optical setups have been aligned with aid of only the spectrum analyzer. Is there a good application note/ reading available that explains the light-path of MIRA 900 (both picosecond and femtosecond configurations) in context of Kerr Lens Modelocking? - I don't know about either. Also some 'protocol' of tuning will be great. We have a manual from Coherent, but I am finding it hard to follow. Regards Shalin On 8/30/07, Guy Cox <[hidden email]> wrote:
Search the CONFOCAL archive at <a href="http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal There are examples of extremely inexpensive autocorrelators being built with a simple LED as the nonlinear detection medium. A quick search of the literature will reveal some papers on this. Using an LED, it is possible to build a reasonable AC for a couple hundred dollars with this method. Craig On 9/4/07, Shalin Mehta <[hidden email]> wrote: > Search the CONFOCAL archive at > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal > Thanks all for reply. > > Given that we provide 1/2 hour for laser to settle is it reasonable to > expect that one can tune the laser thrice a day for different users and > still it works fine? Autocorrelator is too costly for time being but we do > have a spectrum analyzer. Upto now, the optical setups have been aligned > with aid of only the spectrum analyzer. > > Is there a good application note/ reading available that explains the > light-path of MIRA 900 (both picosecond and femtosecond configurations) in > context of Kerr Lens Modelocking? - I don't know about either. Also some > 'protocol' of tuning will be great. We have a manual from Coherent, but I am > finding it hard to follow. > > Regards > Shalin > > On 8/30/07, Guy Cox <[hidden email]> wrote: > > Search the CONFOCAL archive at > http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal > > > > > > Shalin wrote; > > > > What diagnostics do you use for tuning of two photon laser or OPO? Is > laser spectrum analyzer enough? > > > > The laser spectrum analyser should get you back exactly to your > > wavelength, and give a pretty good idea of the pulse length. > > Lastek in Australia make a software system which works with a > > spectrum analyser to give you pulse length and it seems pretty > > good provided it is carefully calibrated. (It's probably sold under > > some other name in the States). > > > > But if you have users who want to know the pulse length precisely > > it's really worthwhile buying an autocorrelator. > > > > > > We have a shared two photon (MIRA 900F Femtosecond configuration) and OPO > from Coherent. One of the main user is very afraid of tuning it - so he > always has a service engineer tune it to 830nm and longest possible pulse > (since he does spectroscopy). There are two more of us who will benefit by > tuning it for two-photon and SHG (different wavelengths and shortest > possible pulse). > > > > 830 is quite OK for SHG (brings the harmonic to 415 which is within > > the range of conventional interference filters (they start to absorb a lot > > at anythong shorter). But it's a bit limiting for 2P. > > > > How is the 'reproducibility' of laser beam profile when working with these > lasers? One of the main concern that other user has is that - if you cannot > come back to exactly 830 nm after tuning to say 740 nm, the custom optical > setup will go out of alignment. > > > > In the early days one make of Ti-S laser was notorious for beam > > wander as you tuned it but even so it should go back when you > > returned it to the original wavelength. Nowadays they seem really > > stable, and I don't think your Mira should be a problem there. The > > only thing I find with a Mira is that it's best to let it warm up for > > half an hour before doing any tweaking of the alignments (and often > > that way you find you didn't really need to do any tweaking anyway). > > > > > Guy > > > > > > -- > My co-ordinates: > Shalin Mehta, Graduate student > Graduate Programme in Bioengineering, NUS, Singapore > Email: shalin {dot} mehta {at} gmail {dot} com > Blog: electricsbm.blogspot.com > Mobile: +65 90694182 |
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Christian Soeller |
Re: what diagnostics to use
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In reply to this post by Shalin Mehta
Search the CONFOCAL archive at
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If you find it hard to follow the manual I recommend you either:
1) Find somebody at your university who has experience in tuning Ti:S lasers, perhaps your physics department might be a good start (or visit a group at a nearby university who work with Ti:S lasers) or 2) You contact your support engineer (presumably from Coherent) to give you/somebody in charge of the instrument a good introduction on how to tune the instrument From then on it is practice, practice, ... A final thought, perhaps there are some training courses out there that others know of? Best of luck, Christian On 5/09/2007, at 12:55 AM, Shalin Mehta wrote: Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Thanks all for reply. -- Christian Soeller PhD Dept. of Physiology +64 9 3737599 x82770 University of Auckland Auckland, New Zealand fax +64 9 3737499 |
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In reply to this post by Shalin Mehta
Search the CONFOCAL archive at
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It's entirely reasonable to
be able to tune the laser as often as
you like - I'd often do it several times in
an hour. The settling
period of half an hour is certainly a wise
precaution. Given
the amount of gear you've got I find it a
bit surpriusing that you
say you can't afford an autocorrelator,
though!
As to the mode of operation, here are the
relevant paragraphs
from my book (details below) which give a
brief overview:
The generation of pulses in a Ti-S laser is essentially passive (though active devices may be added to get things started). As the light passes through the sapphire crystal the intensity of the electric field modifies the refractive index (the Kerr effect) so that it tends to focus the beam. To encourage this a slit is placed in the optical path, so that focussed light will pass more easily than non-focussed light. The end result is that a single pulse forms in the cavity and travels around it, generating the maximum electric field and therefore the maximum degree of self-focussing. The Ti-S laser (but not its pump laser, of course) will work perfectly well with no electrical power. The repetition rate of the laser is the time taken for light to travel around the laser cavity, which explains why the laser is so large, and has a complex folded light path (Figure 8.3). The actual Ti-S crystal is small.
A Ti-sapphire laser has to be pumped with another laser of quite substantial power. Typically the nominal efficiency will be around 10%, so that a 500 mW laser will require 5 W to pump it. For this solid-state neodymium lasers are used. The output from these is in the infrared, at ~1050 nm, and is then doubled in frequency with an LBO crystal which generates a strong second harmonic at 525nm. These are small enough to be fitted into the casing of the Ti-sapphire laser in modern 'one box' systems. The neodymium laser itself needs to be pumped with red light from two or more powerful diode lasers, which are always mounted externally and coupled by an array of optical fibres. The pulses of a Ti-sapphire laser are only a few wavelengths long, and therefore are not monochromatic by the standards of continuous wave lasers. In fact it is possible to estimate the pulse length quite accurately by measuring the spread of wavelengths present. This presents a problem when the laser pulses must travel through a dispersive medium, as in optical components. The (slightly) different wavelengths will travel at different speeds, and the pulses will spread out. Hope this helps.
Guy
Optical Imaging Techniques in Cell
Biology by Guy Cox CRC Press / Taylor & Francis http://www.guycox.com/optical.htm ______________________________________________ Associate Professor Guy Cox, MA, DPhil(Oxon) Electron Microscope Unit, Madsen Building F09, University of Sydney, NSW 2006 ______________________________________________ Phone +61 2 9351 3176 Fax +61 2 9351 7682 Mobile 0413 281 861 ______________________________________________ http://www.guycox.net From: Confocal Microscopy List on behalf of Shalin Mehta Sent: Tue 4/09/2007 10:55 PM To: [hidden email] Subject: Re: what diagnostics to use Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Thanks all for reply.
Given that we provide 1/2 hour for laser to settle is it reasonable to expect that one can tune the laser thrice a day for different users and still it works fine? Autocorrelator is too costly for time being but we do have a spectrum analyzer. Upto now, the optical setups have been aligned with aid of only the spectrum analyzer. Is there a good application note/ reading available that explains the light-path of MIRA 900 (both picosecond and femtosecond configurations) in context of Kerr Lens Modelocking? - I don't know about either. Also some 'protocol' of tuning will be great. We have a manual from Coherent, but I am finding it hard to follow. Regards Shalin On 8/30/07, Guy Cox
<[hidden email]>
wrote:
Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
Thanks for explanation Guy.
We have some Zeiss 'closed' systems at my biology supervisor's place and Olympus 'open' systems at my engineering supervisor's place. My engineering supervisor does have sum of money required to buy autocorrelator but it is tied down in the budget heads of grants that don't allow spending more than 4000 at a time! It seems such grant conditions are quite typical in Singapore.
Regards
Shalin
On 9/5/07, Guy Cox <[hidden email]> wrote:
Search the CONFOCAL archive at <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal" target="_blank"> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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