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Message ID: 2016     Entry time: Thu Feb 11 00:03:24 2016
Author: KojiN 
Type: Misc 
Category: PD QE 
Subject: Beam Adjustment 

For adjusting the beam, the setup was prepared as shown in Fig. 1.

Our taget is 80 um beam waist in radius as shown in Fig. 2.

(Please note that the axes of Fig. 1 and Fig. 2 do not have the same zero point.)

The waist position is not much took care to if the position can be accessed easily.

In our simulation using the beam measured yesterday, when the lens #2 (f=-200 mm) and the lens #3 (f=150 mm) are placed at z = 0.260 m and z = 0.474 m, respectively, the target radius could be obtained at z = 0.74 m.

However, in this setup we cannot obtain the target beam and the waist size seemed to be larger and the waist position seemed to be farther.

Thus the lenses were moved iteratively.

Finally, the lens #2 and #3 are placed at z = 0.114 m and z = 0.483 m, respectively, and the measured beam is as shown in Fig. 3.

(The beam profiler seemed to be saturated. Thus the additional ND filter (O.D.=4.0) is put and the saturation seemed to be extinguished as shown in Fig. 4.)

As a result, the beam waist radius and the beam waist position are 86 um and z = 0.750 m (for the x-direction) and 89 um and z = 0.750 m (for the y-direction), respectively.

These parameters can still be improved by refining the positions of the lens #2 and #3.

Fig. 1 Current setup.
Fig. 2 Target beam.
Fig. 3 Measured data and fitted curves of the beam profile.
Fig. 4 Screen of the beam profiler.


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