Helium optical cryostat with sample in exchange gas: Optistat®CF

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 helium cryostat
• Sample holder and rod
• Up to five sets of windows. (four radial; one axial). Each set includes three windows (inner, radiation shield and outer case windows)
• Cryogen transfer tube
• 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
• Simple height adjust and rotate sample rod: provides sliding adjustment with locking screws to hold a fixed position. The range of vertical motion is 32 mm. Postioning accuracy is 0.5 mm( height) and 1 degree (rotation).
• Precise height adjust and rotate sample rod provides height adjust and with a resolution of 10 µm and a goniometer for setting the rotation angle with a resolution of 12 minutes.
• Liquid cuvette for liquid samples

 Sample environment options

• OptistatCF with static exchange gas: the circulating cryogen does not come into contact with the sample. The heat exchanger is in good thermal contact with the sample space which contains an independent exchnage gas (usually helium). The sample is cooled by conduction through the exchange gas.
• Optistat CF with dynamic exchange gas: temperature stabilised cryogen flows into the exchange gas space cooling the sample directly. This version is recommended for large low conductivity samples or when large heat loads are applied to the sample. Also the cryostat can be used in single shot mode. The sample space is then filled with helium and pumped enabling a base temperature of 1.6 K for approximatey 20 minutes (using an EPS 40 pump).

• If you require a vacuum sample environment then please visit the OptistatCF-V web page. 

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

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.

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).

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.

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.

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.

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 Handong Sun from the Institute of Photonics(Glasgow) is using the OptistatCF to perform experiments of photoluminescence (PL) and PL excitation (PLE) spectra from 5K to 300K on dilute nitrides of III-V semiconductors and related nanostructures. The aim is to elucidate the electronic states and PL mechanisms in this novel material system.