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Message ID: 1869     Entry time: Fri Aug 18 17:01:11 2017
Author: Craig, awade 
Type: Notes 
Category: Laser 
Subject: Notes on Laser Mode Hopping Zones 

This is a brief note on what laser temperature regions Andrew and I found to be bad for mode hopping or otherwise nonlinear behavior.  Laser mode hopping proved to be the main issue we didn't understand for the last three months until Andrew studied the problem carefully (See elogs 1865, 1863, 1858, and 1857). 

After we recalibrated the laser temperatures and increases the slow voltage rails from -2 and 7 volts to the full -10 to 10 volts in elogs 1857 and 1858, we found strong beat notes (precavity value of around -5 dBm) using the slow voltage control at the following voltages:

South: 0.5 V,     North: 8.3 V

South: -7.4 V,    North: 1.9 V

South: -6.73 V,   North: 2.76 V  (This is what we are currently locked at)

Beware of weak precavity beat notes on the order of -40 dBm, we thought these were the main beatnotes for a long time and could never find them on transmission, probably because they were higher order modes beating with a carrier and the HOM didn't make it through the reference cavity.

We also discovered some regions with nonlinear laser frequency behavior (i.e. our strong beatnote would sink to nothing at certain laser temps).  These regions were:

North: Directly below 3.9 V

North: Directly above 4.6 V

North: Directly above 8.8 V

If you are struggling to locate your beatnote, you may be looking with a mode hopping laser.  Try returning to the good zones above.

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