| 6/19/08 we sought to optimize the horizontality of the left prism. We used a 2nd laser and some irises to determine that laser light enters the prism parallel to the optical table's surface. The light reflected and transmitted by the prism, however, were not parallel. The left prism (but not the other) has two knobs underneath it -- one in the upper left and another on the lower right (closest to the table's edge). We determined the following about the functions of these two knobs: -Upper-left knob, turned clockwise, lowers where the reflected light hits an iris and raises where the transmitted light hits another iris. -Lower-right knob, turned clockwise, lowers both of the beams of light exiting the prism. **6/20/08 I actually found the reverse to be true for the lower-right knob. Before adjusting the prism, we fixes two irises such that they were centered on the elevations of the reflected and transmitted light. This way, we can always re-calibrate the prism to this already acceptable alignment in case our adjustments degrade performance. We found, however, that getting the reflected and transmitted light parallel to the table's surface did not cause an appreciable change (improvement or otherwise) to the system's ability to modelock. More experimentation could compare this state to our previously-collected data to see whether there is any notable difference. Here are some spectrometer readings with the horizontal corrections in place. The last one is our "end of day" data.   |
Horizontal Prism |
I am not sure what difference there is between the 1st and 2nd horizontal graphs. Did we take the first one before adjusting the prism, or did the first one occur before you had to work painstakingly to recover modelock? That sounds more like what happened.