Yuhang and Michael

We measured again the RIN of the new Mephisto laser. The laser was sent to a tilted ND filter (prevents back reflection) -> 75mm focal length lens -> PD. The measurements were taken with the spectrum analyser taken out of the clean room.

The relative intensity noise and PD dark noise are shown in figures 1 and 2 (low freq span, high freq span). The units differ between the curves, though the RIN isn't recalibrated by much - the intensity noise was measured from the PD and then divided by the DC value of 0.89 V. For comparison, the KAGRA HP laser RIN shown in Aso-san's LVK presentation is given in figure 3. The new Mephisto laser at TAMA seems to have better RIN than the "Current" KAGRA laser, but not quite as good as the "New" laser.