EYE OPENER
Time
tunnels
IKENOYAMA , JAPAN
Deep in the abandoned
Kamioka mine, is the
world’s most advanced
gravitational wave (GW)
detector. KAGRA is the first
to be built underground,
and the first to use
cryogenically cooled
mirrors. Two 3km-long
arms branch out in an L
shape. A laser, split in two,
is sent hurtling down these
arms and bounced between
the super-cooled mirrors.
When the beams are
recombined and sent into
the detector, their
waveforms will align. That
is, unless a passing GW has
stretched or squeezed one
of the arms. The beams’
wavelengths will not line
up, and the GW is detected.
Yuta Michimura, Assistant
Professor at the University
of Tokyo, explains, “this is
the vacuum chamber. It
houses the fused silica
mirror, OMMT2, which is
curved to reduce the size of
the beam impinging on the
detection photo-diode. The
walls of the entire chamber
are precisely polished, to
reduce the surface area.
Too much surface area
creates too much out
gassing, and that isn’t good
for the vacuum.”
EYE OPENER
ENRICO SACCHETTI
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