Re: SHG

Posted by Craig Brideau on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Re-SHG-tp592071p592072.html

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal I've interspersed a few of my own comments below:

You have to make sure you carefully filter the remaining of the Ti:Sa laser after doubling, so you won't have 2P events
as well.

Typically a good short pass filter centered at 600 or 650 will do the job.  Keep it at right-angles to the beam. 

If the doubling crystal is your own "home built" addition, you don't place it in the Ti:Sa cavity but rather after it.

Yeah, a doubling crystal in the cavity will potentially wreck the laser if it's not built for it.
 

I guess you're using a BBO or LBO, in which case a 5mm by 5mm
piece will be enough, coming to it at a tight focus.

Typically you get a very thin slip of crystal, almost like a microscope cover slip.  Normally this comes mounted in a 1" metal circle or some 'frame' that you can place in an optical mount.
 

Finding the "mismatch" axis and aligning it is a bit tricky and requires 6 degrees of freedom (x-y-z rotational and angular).

If you have a 1/2 waveplate to rotate the polarization of your laser it takes one degree of freedom out of the equation (or that is to say transfers it to the waveplate, which is simple to rotate).  In the case of the waveplate you want to rotate it around the optical axis.  That is to say pretend your laser beam is an axle and the waveplate is a wheel rotating around it.  Adjust the polarization of your laser beam such that it is perpendicular to the table surface.  If you are very lucky your laser might already be this way naturally.  This means you might be able to get away without the waveplate.  The crystal, on the other hand, you want to first align so that it's preferred polarization is the same as the laser, i.e. perpendicular to the table if that's the laser's polarization (or you made it that way with the waveplate).  Usually there's a mark for this on the crystal mount/frame.  You then want to turn the crystal on an axis which is also perpendicular to the table.  Thorlabs and Newport both carry appropriate mounts for doing this sort of thing.  Again, the crystal manufacturers, or even the technical support guys at Thor or Newport, can generally help you out.  Once you get SHG just gently play with all the degrees of freedom until you get a maximum.  Measure the power after the short pass filter and seek the highest value.

Craig

 

Hope this helped- good luck,

Eli


6 degreess

---- Original message ----
>Date: Thu, 8 May 2008 09:34:58 +0800
>From: Peng Xi <[hidden email]>
>Subject: Re: SHG
>To: [hidden email]
>
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Hi Sarah,
>    Just like you asked, it will be an one-photon excitation. So,
>although it is possible that you create a femtosecond 400nm laser pulse,
>it is still linear excitation -- one photon process. Thank you!
>    I am very interested in the experiment itself -- have you tried to
>put a SHG crystal inside the Ti:Sa laser cavity and see the 400nm emission?
>
>Best regards,
>Peng Xi
>Associate Professor
>Institute for Laser Medicine and Biophotonics
>Shanghai Jiao Tong University
>800 Dongchuan Rd.
>Shanghai 200240, China
>Tel: [phone]
>http://biophotonics.sjtu.edu.cn/
>
>
>
>Sarah Kefayati wrote:
>> Search the CONFOCAL archive at
>> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>> Hello all,
>>
>> I appreciate if you could help me with my question:
>>
>> I just want to make sure about this fact that by using a non-linear
>> crystal in the path of my Ti-sapphire laser I will have the frequency
>> doubled beam which excites my sample via traditional one-photon
>> excitation.
>> But dose the intensity of the emitted fluorescence depend on
>> excitation power linearly or quadratically?
>>
>> any information in this regard is highly appreciated.
>>
>> Thanks
>> Sarah

________________________________
Eli Rothenberg, Ph.D.
Post Doctoral Research Associate,
Howard Hughes Medical Institute,
Department of Physics,
University of Illinois,
Urbana-Champaign. 61801.
Illinois, USA
Tel: [phone];
Fax: [phone];
Email: [hidden email]