10.9.3 Misaligned cavity

In this example a misaligned cavity is scanned and the circulating power is detected. Additional spikes in the cavity scan indicate the higher-order modes (order one and two are visible) created by the misalignment (Fig. 114, generated here).

import finesse
from finesse.analysis.actions import Xaxis
finesse.init_plotting()

base = finesse.Model()
base.parse(
    """
    l l1                                # laser with P=1W at the default frequency
    modes(maxtem=3)                     # Hermite-Gauss modes up to n+m = 3

    s s1 l1.p1 ITM.p1 L=1               # a space of 1m length
    m ITM T=0.014 L=35u Rc=-1934        # cavity input mirror
    s scav ITM.p2 ETM.p1 L=3994.5       # cavity length of 3994.5m
    m ETM T=5u L=35u Rc=2245 xbeta=0.3u # cavity end mirror
    cav cav1 ITM.p2                     # computing cavity parameters
    
    pd pd1 ETM.p1.i                     # photodiode measuring the circulating power
    """
)

out = base.run(Xaxis(base.ETM.phi, 'lin', -90, 90, 1000))
out.plot(logy=True);