4号过滤袋:帮帮忙啊！翻译一下

Conventional ring-down measurements involve the injection
of pulses into an extremely high finesse bulk cavity (using
super mirrors of reflectance >99.95%), with the rate of
decay of the output pulse train indicating cavity loss (and
hence the concentration of an absorbing species within the
cavity). The ring-down time, tr, is related to the cavity loss,
_ (in dB), by: tr = 4.34τ/_ where τ is the round trip
cavity time. As has been previously reported [6], we have
developed an alternative method of achieving long ring-down
times in a fibre loop cavity by using an erbium-doped fibre
amplifier to compensate for component losses of the loop.
The introduction of gain within a fibre loop is necessary
for achieving long ring-down times whenever the insertion
loss of the sensor device in the loop becomes significant
(_0.1 dB) [6] as, for example, in our case where we use a
5 cm path-length micro-optic gas cell with an insertion loss of
∼1 dB. For ring-down in passive fibre loops, either evanescent
wave interaction [7–9] or very short path-lengths for small
liquid samples [10] can be used, but here the advantages of
ring-down are somewhat negated by the reduced sensitivity of
the sensing region [6]. On the other hand, the introduction
of gain within a fibre loop presents difficulties relating to
gain control, stability and non-linear effects. Here we present
our results on extended ring-down times in a gain-clamped
optical fibre loop and introduce digital filtering techniques
to efficiently remove unwanted spectral components from the
data arising primarily from relaxation oscillations.