SPECTROSCOPY
Windows for cryogenic environments
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Extensive choice to suit yourexperimental needs

Many cryostats are used in experiments where the samples must be irradiated or
measurements made on emitted radiation from such samples. Appropriate windows must befitted to your cryostat to permit radiation to pass through the sample space.
Window materials
The type of window material selected will be determined by the wavelength and intensity of the radiation, the environmental
temperature and whether or not beam polarisation is required. Oxford Instruments offers a wide range of different windowmaterials.

Window mounting
Room temperature windows which must be vacuum tight are generally sealed onto a rubber ‘O’ ring. The mounting methodminimises strain on the windows and allows easy removal if required. Radiation shield windows do not need to be vacuum
tight but it is important that they are thermally anchored. This is achieved by retaining the window in a copper mount using aspring clip. The windows on sample cells must be vacuum tight at low temperatures and two sealing methods, indium or copper
gaskets, are used depending on whether the upper temperature is limited to 300 K or 500 K respectively.

Spectrosil B

100

Specrosil B is a synthetic vitreous silica.
The material itself is not birefringent

Transmission (%)

80and standard strain-relieved low
temperature window mounts ensure

60

that Spectrosil B windows do notaffect polarised light. It is an excellent
material for filtering out the near-40

mid IR room temperature thermalradiation, resulting in a low thermal

20

load on the cryostat. The transmission
data is for a 2 mm thick window.

00.1

1
Wavelength (μm)

10Windows for cryogenic environments

100

80

60Transmission (%)

40

Spectrosil WF

20Spectrosil WF is a water free synthetic
vitreous silica. It has the same material

00.1

101
Wavelength (μm)

a transmission range which extends
further into the IR. The transmission

100

data is for a 2 mm thick window.

80Transmission (%)

characteristics as Spectrosil B, but has

Sapphire
Sapphire is an alternative window

60

for visible and near IR applications.
It is the only window which may be40

used at high temperatures (up to 500

10 KK). At temperatures below 80 K the300 K

20transmission of sapphire increases inthe extreme IR region. This effect allows
sapphire to be used as a cold inner

00.11

1110100

1000

Wavelength (μm)

window for IR measurements. Sapphireis birefringent. The transmission data isfor a 2 mm thick window.

100Polypropylene

80
Transmission (%)

Polypropylene is a polymer with a usefultransmission range which runs from60

0.2 μm to the millimetre region with
only a few absorption bands in themid IR. At temperatures above 100 K

40this material is porous to helium gas.
The transmission data is for a window

2060 μm thick which may be used as acold window to temperatures as low

0as 1.5 K. Polypropylene windows may

0.11

1110
Wavelength (μm)

100

1000

be damaged if used with high power
optical beams.

Windows for cryogenic environments

SPECTROSCOPY
Crystalline quartz

100

Crystalline quartz is a window for the80

visible and near IR. It exhibits a strong

Transmission (%)

temperature dependence in the far
IR. At temperatures below 80 K the60

transmission is greater than 70% forwavelengths greater than 80 μm.
This material may be used as a cold40

2010 K

inner window for far IR applications.

300 K

Crystalline quartz is birefringent andis available cut with the z-axis normal
to the window to reduce polarisation
effects. The transmission data is for a 200.11

1110100

1000mm thick window.

Wavelength (μm)

100Calcium fluoride
Calcium fluoride may be used in theTransmission (%)

80

near and mid IR. It cannot be used
as a cold inner window due to its
mechanical and thermal properties. The60

transmission data is for a 2 mm thickwindow.

40

2000.1

1
Wavelength (μm)

10Windows for cryogenic environments

OPTICAL100

KRS 5
KRS 5 (Thallium Bromide-Thallium Iodide)80

is a useful window for the mid IR. The

Transmission (%)

complex nature of the cold window
mount and the necessity to make it

60

vacuum tight results in the clear accessdiameter being reduced by 2 mm when40

compared with other materials. Thematerial is toxic and should be handledwith care.

2000.1110100

Wavelength (μm)

100Zinc selenide
Zinc selenide is a reliable cryogenicTransmission (%)

80

window for the mid IR. Care should betaken with handling as it is toxic andscratches easily. The transmission data is

60for a 2 mm thick window.

40

2000.1

1

10010

Wavelength (μm)

Windows for cryogenic environments

S
100

80

60

Transmission (%)

40

Polythene

20

Polythene is a polymer which may be
used in the extreme IR. The material is010100
Wavelength (μm)

1000

porous to helium gas above 100 K. The
transmission data is for a 1 mm thickwindow.

100

MylarTM
Mylar™ is a polyester film. StandardTransmission (%)

80

windows are 125 μm thick and may
be used as a cryogenic window in theextreme IR. Mylar is porous to helium

60

gas above 100 K.

40

Aluminised MylarTM

20

Aluminised Mylar™ is a useful window
for X-ray and gamma ray applications.

010100
Wavelength (μm)

1000

For X-rays its transmission is greater than
90% with some diffuse scattering atlow angles. Standard windows are 125
μm thick with a 0.3 μm thick aluminium
coating on one side.

visit www.oxford-instruments.com for more information

3072

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