This file demonstrates the use of a modulator. Phase modulation (with up to five higher harmonics is
applied to a laser beam and amplitude detectors are used to measure the field at the first three harmonics.
Compare this to Figure 16 as well.
Finesse input file for ‘Modulation index’
laser i1 1 0 n0 % laser P=1W f_offset=0Hz
mod eom1 40k .05 5 pm n0 n1 % phase modulator f_mod=40kHz, modulation index=0.05
ad bessel1 40k n1 % amplitude detector f=40kHz
ad bessel2 80k n1 % amplitude detector f=80kHz
ad bessel3 120k n1 % amplitude detector f=120kHz
xaxis eom1 midx lin 0 10 1000 % x-axis: modulation index of eom1
yaxis abs % y-axis: plot ‘absolute’ amplitude
Finesse offers two different types of modulators: the ‘modulator’ component shown in the example above, and the ‘fsig’ command, which can be used to apply a signal modulation to existing optical components. The main difference is that ‘fsig’ is meant to be used for transfer function computations. Consequently Finesse discards all nonlinear terms, which means that the sideband amplitude is proportional to the signal amplitude and harmonics are not created.
Finesse input file for ‘Mirror modulation’
laser i1 1 0 n1 % laser P=1W foffset=0Hz
space s1 1 1 n1 n2 % space of 1m length
bs b1 1 0 0 0 n2 n3 dump dump % beam splitter as ‘turning mirror’, normal incidence
space s2 1 1 n3 n4 % another space of 1m length
fsig sig1 b1 40k 1 0 % signal modulation applied to beam splitter b1
ad upper 40k n4 % amplitude detector f=40kHz
ad lower -40k n4 % amplitude detector f=-40kHz
ad harmonic 80k n4 % amplitude detector f=80kHz
xaxis sig1 amp lin 1 10 100 % x-axis: amplitude of signal modulation
yaxis abs % y-axis: plot ‘absolute’ amplitude
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