Helium optical cryostat with sample in vacuum: Optistat®CF-V

<4K continuous flow optical cryostat ideal for experiments large requiring a large sample space and minimum of windows in the optical beam path (reducing reflective losses). It is also a very versatile instruments as its tail is interchangeable between MicrostatHe2 and MicrostatHe2 Rectangular tail, ideal for microscopy and Magneto-optical Kerr effect experiments.

Wide temperature range: from 3.2 K to 500 K
Large sample space enabling studies of sample with a wide range of size and geometry
Superb optical access (f/0.9) for measurements requiring light collection
Optimised clear beam throughput (23 mm diameter aperture) allows a large illumination area for measurements involving the detection of low intensity light
The most economical use of cryogens on the market: less than 0.45 L/h at 4.2 K using a Low Loss Transfer tube
No cold windows enabling the use of any window material above 300 K
Demountable radiation shield windows to maximise transmission intensity
Compact size allowing easy integration into commercial spectrometers
Electrical measurements via 10-pin electrical feed wire to heat exchanger
Can be operated in pull mode (using a gas flow pump to pull the helium from a storage dewar to the sample space) or push mode (by pressurising the storage dewar).

The core "cold unit" of the OptistatCF-V, MicrostatHe and MicrostatHe Rectangular Tail is interchangeable, enabling a modular set of optical cryostats for different experimental set-ups by swapping only the outer body.

Specification
System components/options
Operation
Applications
Images

Layout and dimensions

OptistatCF-V liquid helium (LHe) continuous flow optical cryostat layout and dimensions

Specifications

Mode of operation	‘Pull’ mode	‘Push’ mode
Temperature range	3.2-500 K with GF4 pump	4.2-500 K
	2.3-500 K with EPS40 pump
Sample holder dimensions	20 mm wide x 50 mm long (optical sample holder version has a 12.5 mm aperture)
Maximum sample space (space within radiation shield)	30mm wide x 58mm long
Temperature stability	+/- 0.1 K (measured over 10 min period)
Cool down from ambient to 4.2 K	10 minutes
Cool down helium consumption from ambient to 4.2 K	<1.3 litres
Helium consumption at 4.2 K	<0.45 l/h (see Note 1)
Sample change time	1 hour
Cryostat weight	2 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

A typical system consists of:

OptistatCF-V helium cryostat including cooling unit and OptistatCF-V tail set
Sample holder
Up to five sets of windows. (four radial; one axial). Each set includes two windows (radiation shield and outer case windows)
Cryogen transfer tube: LLT 700
New Mercury iTC temperature controller
High vacuum pumping system
Helium dewar

Optional items:

Gas flow pump
Gas flow controller
Automated transfer tube allowing fully automated control across the entire temperature range
Wiring and electrical connections to the sample

Window options

A wide range of window materials can be fitted to the OptistatCF-V 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

Transfer lines:

Oxford Instruments Low Loss Transfer tubes (LLT) use the cold gas exiting the cryostat to cool the shields surrounding the incoming liquid within the transfer tube. As a result, the consumption of our cryostats is the lowest on the market, dramatically reducing your running costs.

We can also offer an extra flexible transfer tube for those with restricted space in their labs. Please note that as this does not use the gas cooled mechanism, helium consumption will be higher than for the LLT range. However it will be well suited to those who need a lightweight and more flexible transfer tube.
An auto needle valve can be fitted to the LLT which allows the temperature controller to optimise the helium flow rate

New Oxsoft IDK instrument development kit software

With the new Oxsoft IDK you have new levels of control. You can design remote control and configuration programs and integrate your system into your preferred experiment control architecture.

See also the OptistatCF for this cryostat with sample in exchange gas

The OptistatCF-V 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).

The cryogen is regulated by a needle valve on the transfer tube.

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).

The advantage of the pull mode operation is that the storage dewar pressure does not need to be monitored (since it remains at 1 atmosphere), the cryostat can reach a lower base temperature and the helium flow stability is improved. The advantage of the push mode operation is that the need for a gas flow pump is removed thus saving cost and eliminating the noise and vibration generated by pressurising the storage dewar.

The sample is positioned on the sample holder in good thermal contact with the heat exchanger and surrounded by a vacuum.

Temperature control is achieved by a combination of manual helium flow control and power dissipated in an electrical heater, regulated using a temperature controller. The temperature is monitored by a rhodium iron temperature sensor fitted on the heat exchanger. To monitor the temperature at the sample position, an extra temperature sensor can be fitted at the sample position.

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

To change the sample, the cryostat is warmed to room temperature, the vacuum released and the outer case and radiation shield removed.

The OptistatCF-V 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.

Case study:

Dr Martin Kemerink and Mr HAns Gommans at the university of Eindhoven (Netherlands) are using the OptistatCF-V to conduct I-V characterisation and admittance spectroscopy on plastic solar cells. More specifically, their aim is to determine the electron and hole mobilities in these condensed organic blends at various temperatures in order to pinpoint the physical origin of conduction.