Optistat®CF liquid helium (LHe) continuous flow optical cryostat

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A liquid helium cooled, top loading continuous flow (CF) cryostat enabling optical spectroscopy experiments that require:

Base temperature down to 2.3 K
Large 20 mm diameter sample space
Quick sample change via top loading, with sample in exchange gas
Generous f1 radial optical access with 4 radial windows and 1 axial window, with a wide range of window materials available
Operation in any orientation

Specifications
System components/options
Operation
Applications
Images

	Static exchange gas		Dynamic exchange gas
Mode of operation	‘Pull’ mode	‘Push’ mode	‘Pull’ mode	‘Push’ mode
Temperature range	3.4-300 K with GF4 pump	4.2-300 K	3.4-300 K with GF4 pump	4.2-300 K
	2.3-300 K with EPS40 pump		2.3-300 K with EPS40 pump
			1.6-300 K in single shot
	500 K as an option
Temperature stability	+/- 0.1 K (measured over 10 minute period)
Maximum sample space available	20 mm diameter
Sample holder dimensions	19 mm wide x 30 mm long (Optical sample holder version has a 15 mm aperture)
Cooldown time from ambient to 4.2 K	25 minutes (35 minutes for the 500 K option)
Cooldown helium consumption from ambient to 4.2 K	1.5 litres
Helium consumption at 4.2 K	< 0.55 l/h (using LLT600, see note 1)
Sample change time	5 minutes
Cryostat weight	3.7 kg

Notes:

1. All specifications refer to the base model cryostat with two sets of Spectrosil B windows used with an LLT transfer tube and an ITC controller.

Sample emvironment options

Choose the static exchange gas version to cool the sample by conduction only and exclude liquid helium from the optical path
Choose the dynamic exchange gas option to cool the sample directly
See also the OptistatCF-V for this cryostat with sample in vacuum

Window options

A wide range of window materials can be fitted to the OptistatCF to meet specific spectroscopy applications
Special windows with non-parallel faces and anti-reflection coatings are available
Additional or replacement window flanges available via the Oxford Instruments Direct - Cryospares® on-line catalogue

Pump options

A simple oil-free vane pump GF4 is supplied for operation to 3.4 K
Lower temperatures to 2.3 K require an EPS40 single stage rotary pump; this also extends the base temperature for the dynamic exchange gas version to 1.6 K

Temperature control and options

Flexible single- or 3-channel ITC503
Both static and dynamic exchange gas OptistatCF versions are available with the upper temperature limit extended to 500 K

LHe transfer

Choose a Low Loss transfer tube LLT600 to further minimise liquid helium consumption
An auto needle valve can be fitted to the LLT which allows the ITC503 temperature controller to optimise the helium flow rate
Alternatively, specify a TTL200 lightweight liquid helium transfer tube

Software control

Oxford Instruments electronics products are controllable through the OxSoft software using RS232, ISOBUS or GPIB interfaces
LabVIEW virtual instruments are provided for Oxford Instruments electronics products to allow full PC-based control and monitoring. These can be integrated into a complete LabVIEW data acquisition system

The OptistatCF works on a continuous flow principle using an oil-free pump to draw liquid helium from a storage dewar, along a transfer tube, to the heat exchanger ("pull" mode). If the noise and vibration from the pump are undesirable then helium liquid can be pushed through the heat exchanger by pressurising the storage vessel ("push" mode).

Temperature control is achieved by a combination of manual helium flow control and power dissipated in an electrical heater, regulated using an ITC temperature controller.

OptistatCF and CF-V liquid helium continuous flow optical cryostat operating principle

Changing the sample simply involves removing the sample rod, maintaining over-pressure of the exchange gas, replacing the sample and inserting the sample rod back into the cryostat. There is no need to break the insulating vacuum or warm the cryostat up. The resulting sample change times are very short, typically few minutes.

The OptistatCF will also operate with liquid nitrogen (LN2) as coolant for measurements to 80 K.

UV / Visible spectroscopy: Experiments at low temperatures reveal the interaction between the electronic energy levels and vibrational modes in solids.

Infrared spectroscopy : Low temperature IR spectroscopy is used to measure changes in interatomic vibrational modes as well as other phenomena such as the energy gap in a superconductor below its transition temperature.

Raman spectroscopy : Lower temperatures result in narrower lines associated with the observed Raman excitations.

Photoluminescence : At low temperatures, spectral features are sharper and more intense, thereby increasing the amount of information available.

SPM, STM, AFM : Low temperatures decrease the thermal noise from the probes and reduce atomic vibrations.