<s>
A	O
transition-edge	B-Algorithm
sensor	I-Algorithm
(	O
TES	O
)	O
is	O
a	O
type	O
of	O
cryogenic	O
energy	O
sensor	O
or	O
cryogenic	B-Algorithm
particle	I-Algorithm
detector	I-Algorithm
that	O
exploits	O
the	O
strongly	O
temperature-dependent	O
resistance	O
of	O
the	O
superconducting	O
phase	O
transition	O
.	O
</s>
<s>
D	O
.	O
H	O
.	O
Andrews	O
demonstrated	O
the	O
first	O
transition-edge	O
bolometer	B-Application
,	O
a	O
current-biased	O
tantalum	O
wire	O
which	O
he	O
used	O
to	O
measure	O
an	O
infrared	O
signal	O
.	O
</s>
<s>
Subsequently	O
he	O
demonstrated	O
a	O
transition-edge	O
calorimeter	B-Algorithm
made	O
of	O
niobium	O
nitride	O
which	O
was	O
used	O
to	O
measure	O
alpha	O
particles	O
.	O
</s>
<s>
The	O
thermal	O
runaway	O
problem	O
was	O
solved	O
in	O
1995	O
by	O
K	O
.	O
D	O
.	O
Irwin	O
by	O
voltage-biasing	O
the	O
TES	O
,	O
establishing	O
stable	O
negative	O
electrothermal	O
feedback	O
,	O
and	O
coupling	O
them	O
to	O
superconducting	O
quantum	O
interference	O
devices	O
(	O
SQUID	B-Protocol
)	O
current	O
amplifiers	O
.	O
</s>
<s>
When	O
a	O
photon	B-Application
is	O
absorbed	O
by	O
the	O
TES	O
,	O
this	O
extra	O
power	O
is	O
removed	O
by	O
negative	O
electrothermal	O
feedback	O
:	O
the	O
TES	O
resistance	O
increases	O
,	O
causing	O
a	O
drop	O
in	O
TES	O
current	O
;	O
the	O
Joule	O
power	O
in	O
turn	O
drops	O
,	O
cooling	O
the	O
device	O
back	O
to	O
its	O
equilibrium	O
state	O
in	O
the	O
self-biased	O
region	O
.	O
</s>
<s>
In	O
a	O
common	O
SQUID	B-Protocol
readout	O
system	O
,	O
the	O
TES	O
is	O
operated	O
in	O
series	O
with	O
the	O
input	O
coil	O
L	O
,	O
which	O
is	O
inductively	O
coupled	O
to	O
a	O
SQUID	B-Protocol
series-array	O
.	O
</s>
<s>
Thus	O
a	O
change	O
in	O
TES	O
current	O
manifests	O
as	O
a	O
change	O
in	O
the	O
input	O
flux	B-General_Concept
to	O
the	O
SQUID	B-Protocol
,	O
whose	O
output	O
is	O
further	O
amplified	O
and	O
read	O
by	O
room-temperature	O
electronics	O
.	O
</s>
<s>
Any	O
bolometric	B-Application
sensor	O
employs	O
three	O
basic	O
components	O
:	O
an	O
absorber	O
of	O
incident	O
energy	O
,	O
a	O
thermometer	O
for	O
measuring	O
this	O
energy	O
,	O
and	O
a	O
thermal	O
link	O
to	O
base	O
temperature	O
to	O
dissipate	O
the	O
absorbed	O
energy	O
and	O
cool	O
the	O
detector	O
.	O
</s>
<s>
These	O
devices	O
generally	O
utilize	O
a	O
tungsten	B-Application
TES	O
as	O
its	O
own	O
absorber	O
,	O
which	O
absorbs	O
up	O
to	O
20%	O
of	O
the	O
incident	O
radiation	O
.	O
</s>
<s>
At	O
higher	O
energies	O
,	O
the	O
primary	O
obstacle	O
to	O
absorption	O
is	O
transmission	O
,	O
not	O
reflection	O
,	O
and	O
thus	O
an	O
absorber	O
with	O
high	O
photon	B-Application
stopping	O
power	O
and	O
low	O
heat	O
capacity	O
is	O
desirable	O
;	O
a	O
bismuth	B-Algorithm
film	O
is	O
often	O
employed	O
.	O
</s>
<s>
Tungsten	B-Application
has	O
been	O
a	O
popular	O
choice	O
for	O
elemental	O
TESs	O
as	O
thin-film	O
tungsten	B-Application
displays	O
two	O
phases	O
,	O
one	O
with	O
Tc	O
~	O
15	O
mK	O
and	O
the	O
other	O
with	O
Tc	O
~	O
1	O
–	O
4	O
K	O
,	O
which	O
can	O
be	O
combined	O
to	O
finely	O
tune	O
the	O
overall	O
device	O
Tc	O
.	O
</s>
<s>
Two	O
approaches	O
to	O
control	O
the	O
thermal	O
link	O
are	O
by	O
electron	O
–	O
phonon	B-Language
coupling	O
and	O
by	O
mechanical	O
machining	O
.	O
</s>
<s>
At	O
cryogenic	O
temperatures	O
,	O
the	O
electron	O
and	O
phonon	B-Language
systems	O
in	O
a	O
material	O
can	O
become	O
only	O
weakly	O
coupled	O
.	O
</s>
<s>
The	O
electron	O
–	O
phonon	B-Language
thermal	O
conductance	O
is	O
strongly	O
temperature-dependent	O
,	O
and	O
hence	O
the	O
thermal	O
conductance	O
can	O
be	O
tuned	O
by	O
adjusting	O
Tc	O
.	O
</s>
<s>
TES	O
single-photon	O
detectors	O
suffer	O
nonetheless	O
from	O
a	O
few	O
disadvantages	O
as	O
compared	O
to	O
their	O
avalanche	O
photodiode	O
(	O
APD	O
)	O
counterparts	O
.	O
</s>
<s>
APDs	O
are	O
manufactured	O
in	O
small	O
modules	O
,	O
which	O
count	O
photons	B-Application
out-of-the-box	O
with	O
a	O
dead	O
time	O
of	O
a	O
few	O
nanoseconds	O
and	O
output	O
a	O
pulse	O
corresponding	O
to	O
each	O
photon	B-Application
with	O
a	O
jitter	O
of	O
tens	O
of	O
picoseconds	O
.	O
</s>
<s>
In	O
contrast	O
,	O
TES	O
detectors	O
must	O
be	O
operated	O
in	O
a	O
cryogenic	O
environment	O
,	O
output	O
a	O
signal	O
that	O
must	O
be	O
further	O
analyzed	O
to	O
identify	O
photons	B-Application
,	O
and	O
have	O
a	O
jitter	O
of	O
approximately	O
100	O
ns	O
.	O
</s>
<s>
Furthermore	O
,	O
a	O
single-photon	O
spike	O
on	O
a	O
TES	O
detector	O
lasts	O
on	O
the	O
order	O
of	O
microseconds	O
.	O
</s>
