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Entry  Wed Jun 2 01:47:28 2010, Alberto, Kiwamu, Update, IOO, mode measurement of new input optics afterMMT1.pngbeam_profile.pngMMT1_.dat.zipinside_vac_2.png
    Reply  Wed Jun 2 03:50:03 2010, Koji, Update, IOO, mode measurement of new input optics 
       Reply  Thu Jun 3 13:14:27 2010, kiwamu, Update, IOO, mode measurement of new input optics inside_vac_2.png
          Reply  Thu Jun 3 14:01:51 2010, kiwamu, Update, IOO, mode measurement of new input optics check_measurement_edit.png
             Reply  Thu Jun 3 14:13:20 2010, Jenne, Update, IOO, mode measurement of new input optics 
    Reply  Thu Jun 3 14:40:28 2010, Alberto, Kiwamu, Update, IOO, mode measurement of new input optics 
       Reply  Tue Jun 8 00:38:22 2010, Koji, Kiwamu, Update, IOO, improved Gaussian beam in new IOO 2010-6-7_2.png
          Reply  Fri Jun 11 14:31:04 2010, kiwamu, Update, IOO, mode matching of new IOO profile_MMT.pngdist_MMO.png
Message ID: 3029     Entry time: Wed Jun 2 01:47:28 2010     Reply to this: 3031   3046
Author: Alberto, Kiwamu 
Type: Update 
Category: IOO 
Subject: mode measurement of new input optics 

The mode profile of the new input optics was measured.

Although the distance between each optic was not exactly the same as the design because of narrow space,

we measured the profile after the curved mirror (MMT1) that Jenne and Kevin put in the last week.

 


(interference from MMT1)

Below is a sketch of the current optical path inside of the chamber.

inside_vac_2.png

 

In the beginning of this measurement, the angle between the incident and the reflection on MMT1 (denoted as theta on the sketch) was relatively big (~40deg) although MMT1 was actually made for 0deg incident.

At that time we found a spatially large interference imposed on the Gaussian beam at the beam scan. This is not good for mode measurement

This bad interference can be caused by an extra reflection from the back surface of MMT1 because the interference completely vanished by removing MMT1  .

In order to reduce the interference we decreased the angle theta as small as possible. Actually we made it less than 10deg which was our best due to narrow space. 

Now the interference got less and the spot looks better.

The picture below shows an example of the beam shape taken by using the beam scan.

Top panel represents the horizontal mode and bottom panel represents the vertical mode.

You can see some bumps caused by the interference on the horizontal mode, these bumps may lead to overestimation of the horizontal spot size .

 

beam_profile.png

 

(result)

 afterMMT1.png

 The above plot shows the result of the mode measurement.

 Here are the parameter obtained by fitting. The data is also attached as attachment:4

waist size for vertical  w0v [mm]  0.509 +/-0.0237
waist size for horizontal

w0h  [mm]

 0.537  +/- 0.0150
waist position from MMT1 for vertical  xv[m]  -2.91 +/- 0.214
waist position from MMT1 for horizontal xh[m]   -2.90 +/-  0.127


Attachment 3: MMT1_.dat.zip  378 Bytes  Uploaded Wed Jun 2 04:31:41 2010
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