Thursday we optimized the AOM trasmission looking the intensity of the first order beam and addressing it on the green path, after the pass in the AOM (AOM in double pass).
It was then aligned trough the second green telescope (GL3 and GL5) and send to SQB1 with the threee steering mirrors GM5, GM6 and GM7. At the end of the shift, the green beam (GB) was left injected on SQB1, impinging at the center of SQB1_M11 and propagatind trough di dichroic SQB1_M21 and the last holed screen at beginning of the SQB1-SQB2 minilink.
Friday 23th we characterized the conversion efficiency on the first order, measuring the its power at the first pass (i.e. just after the lensis GLAOM) and of the double pass trasmission, i.e. after EQB1_GM3 after the fine optimization with the fine adjustment of the AOM angle w.r.t. the impinging beam directon.
(N.B.: The AOM is in double pass configuration: the beaam is focalized in the AOM by means of the first telescope (GL1 and GL2). The halfplate and the polirizing beam splitter (GHWP1 and GPB) address the beam on the AOM were is diffracted and more then five higher diffracted and frequency shiftrd beams emerge with the main (zero order) not deviated. An iris selects the first difracted order, shifted of Ω w.r.t the carrier. Aftoer a QWP, this is the focused on a 0° AOI mirror and retroreflected into the AOM with orthogonal polarizaton, so that is then reflected by the PBS see attached figure).
AOM efficiency:
GreenPower =23.7 mW (measured after GL2)
PBS transmitted power ratio: 8 mW /23.7 mW = 0.34 +/- 0.1
(we worked with lower power w.e.t the available to avoid beam profiler saturation)
- FIrst order power ratio ~ 6.83 +/- .01 mW on 8 +/- .01 mW with ; -4.5 dB RF amplitude => 85.0 +/- 0.2 %
- Power ratio on the double pass: 2.01 /2.78 = 0.72 +/-.02
(on the double pass, the carrier is the selected single pass 1th order).
The power has been measured after GPBS, it is the reflected beam. In agreement with the GHWP setting. This correspond ~ 34% of the total power of the entering beam, i.e. 0.34*6.83 mW)
EOM QUBiG INSTALLED:
- EOM trasmitted ratio : 1.54/1.61 = 0.97 +/- 0.02
NEXt steps:
- EQB1 Green detectors palcement and first alignment
- CHaracerization of the green beam at the EQB1 out and alignment toward SQB2
