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Entry  Tue May 8 16:28:30 2012, tara, Notes, Laser, external cavity laser diode IMG_0887.jpgIMG_0888.jpg
    Reply  Wed May 9 22:26:26 2012, tara, Notes, Laser, external cavity laser diode 
       Reply  Wed Feb 13 19:54:32 2013, tara, Notes, Laser, external cavity laser diode 
Message ID: 1099     Entry time: Wed Feb 13 19:54:32 2013     In reply to: 957
Author: tara 
Type: Notes 
Category: Laser 
Subject: external cavity laser diode 

Some notes about external cavity diode laser. I investigated in this about a year ago.  I think it might be a good time to work on it, since I'm modifying the  ctn layout and we can use a frequency stabilized laser (although locked to a short cavity) via fiber optic to test with a home made ecdl. 


I just asked Aki a few more questions about the ecd laser. If we do not require the performance to be rival to that of the NPRO, making one is possible in a few weeks time scale.

Q1) The setup of the Littrow style laser you showed me had one mirror
behind the grating. Is the setup similar to this
http://rsi.aip.org/resource/1/rsinak/v72/i12/p4477_s1>? Where the
mirror is used so that the alignment does not change when the laser is

A1) Actually, Yes, for the laser you took the photo. But, most of the lasers we use in the lab don't have a mirror, only diode and grating in the box. In our case, we only scan the frequency by ~1GHz and the pointing vector drift is negligible.


Q2) Did you remove the glass window of the diode laser when you assemble
 the laser? If so, how do you keep the diode clean, or it does not matter
for your requirement.

A2) We didn't remove the glass window. What we did is very simple. We mounted the bare diode on the thorlabs mount: http://www.thorlabs.com/thorProduct.cfm?partNumber=LT230220P-B


 Q3) You mentioned that the line width of the laser when locked to CS cell
is ~300kHz. Is it because of gain limited of the servo or the CS cell's
intrinsic noise?

A3) We haven't measure the linewidth with locking and without locking independently. It's possible that our laser linewidth (without frequency lock) might be ~300kHz. So I don't know what limits our linewidth.

One thing you may want to consider is that a diode laser is infamous for the broad background incoherent light, compared to the solid state lasers. We typically observe ~30nm-wide incoherent light around the carrier with 30-40dB suppression compared to the carrier. If your experiment is sensitive to the spectral purity, this might be an issue.



 So the question is do we want to try to build one similar to what they have? We know that with the time scale and experience we have it will not be as good as the performance of the ecd laser reported in Numata etal paper, but it might be a fun project for the SURF student.


I'm looking into how to make external cavity diode laser (ecd).

Here is the list of what we need.


  • Laser diode 1064nm, diode (+AR coating)
  • Grating
  • Current driver for locking the laser (home made)

I ask Akihisa who works in Kimble's group about their home made 850 nm ecl. The performance is not as good as NPRO yet (300kHz line width when locked to CS cell), but it is certainly interesting.

  • They use Littrow configuration ( 1 grating to form a cavity). The mirror behind the grating is for adjusting the output beam.
  • The PD is not AR coated, a slight power (10 uW) that transmits inside the diode is enough for the feedback.
  • The linewidth is ~ 300kHz when locked to CS cell, the free running noise is not measured.
  • They use both PZT and current to actuate on the frequency stabilization, the bandwidth is 50kHz.
  • Temperature feedback is employed to keep the stability of the laser
  • Time for putting everything in the box (once all components are ready) is ~ 1wk

 (IMG_0887.jpg IMG_0888.jpg



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