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Micro-Raman Cryostat: LT3-OM

  • Overview
  • Specifications
  • Drawings
  • Pictures
Micro-Raman cryostat: LT3-OM MG with a magnet post.
Micro-Raman cryostat installed on Microscope at the University of Tennessee, Knoxville. Courtesy of Prof. Janice Musfeldt

With unique features not found in other cryostats, the LT3-OM is designed for Micro-Raman spectroscopy experiments, as well as other types of low-vibration spectroscopy and microscopy experiments. A slim 1.52" profile allows the Micro-Raman cryostat to fit on most microscope stages. Also it has a continuously adjustable sample holder, enabling the user to fine tune the placement of the sample within the working distance of their microscopy system.

Click here to download the LT3-OM data sheet (PDF).

The Micro-Raman cryostat’s vacuum shroud is constructed entirely of polished, welded stainless steel for a cleaner sample environment. The smooth durable stainless steel finish limits the residual vapor pressure (partial pressure) of water and oil, and reduces the probability of mono layers of water forming on the sample surface. This leads to no water peaks during the experiment.

The Micro-Raman cryostat benefits from all of the features that set the ARS manufactured LT3 cryostats apart from all other flow cryostats, including the coaxial shield flow transfer line and matrix heat exchanger for low helium consumption and high cooling power.

Click here to see more Advanced Research Systems flow cryostats.

Applications
  • Optical microscopy
  • Micro-Raman
  • Quantum dots
  • Photoluminescence
  • Micro-photoluminescense
  • Electro-optical
  • Magneto-optical
Features
  • Continuously adjustable sample height
  • Slim 1.52" profile
  • Nanometer level vibrations
  • Liquid helium flow
  • Matrix heat exchanger
  • Co-axial shield flow
  • 4 K liquid helium operation (1.7 K with pumping)
  • 0.7 LL/hr liquid helium consumption at 4.2 K
  • Liquid nitrogen compatible (77 K operation)
  • Precision flow control
Typical Configuration
  • Cold head (LT3-OM)
  • Co-axial shield flow liquid helium transfer line
  • Stainless steel instrumentation skirt
  • Dewar adapter
  • Flow meter panel for helium flow control and optimization
  • Nickel plated OFHC copper radiation shield
  • Instrumentation for temperature measurement and control:
    • 10 pin hermetic feedthrough
    • 36 ohm thermofoil heater
    • Silicon diode sensor curve matched to (± 0.5 K) for control
    • Calibrated silicon diode sensor (±12 mK) with 4 in. free length for accurate for sample measurement
  • Flat plate sample holder for optical experiments
  • Temperature controller
Options and Upgrades
  • Transmission upgrade
  • Magnet post upgrade (to fit the warm bore of a magnet)
  • High flow transfer line
  • High temperature interface
  • Very high temperature interface
  • Custom temperature sensor configuration (please contact our sales staff)
  • Custom wiring configurations (please contact our sales staff)
  • Sample holder upgrades (custom sample holders available)
  • Window material upgrades (custom materials available)

The ARS Advantage

Matrix Heat Exchanger
The Matrix Heat Exchanger is Imbedded in the Cold Tip of the Helitran Flow Cryostat

The Helitran® incorporates an extended surface tip heat exchanger (Matrix Heat Exchanger)  which provides efficient heat transfer between the helium and the sample mount.  The liquid helium flows through this heat exchanger and as the latent heat of  vaporization cools the sample mount,  the liquid evaporates. The gas continues to flow through the exchanger, providing additional cooling by capturing the enthalpy of the gas. If the flow is optimized the helium gas will exit the Matrix Heat Exchanger at a temperature equal to the sample temperature.

Without an extended surface cryostat tip heat exchanger, the consumption of helium during initial cooldown is 40 times higher from 300 K (room temperature) to 4.2 K, and 14 times higher when cooling from 77 K to 4.2 K.

Co-axial Shield Flow
A Schematic Representation of the Coaxial Shield Flow Transferline

Conventional helium flow cryostats utilize a capillary tube in a vacuum jacket with super insulation to reduce the radiant heat load.  However as the helium absorbs radiant heat, the liquid is vaporized and forms bubbles of gas which have a larger volume than the liquid, thus forming a temporary block to the flow of the liquid. This is called “vapor binding.”  At the delivery end of the transfer line this results in the liquid/gas mixture being delivered in spurts, with accompanying pressure and temperature cycling.

The coaxial flow transfer line incorporates a shield flow surrounding the tip flow for the entire length of the transfer line. The entrance to the coaxial shield flow tube is provided with a nozzle which results in a pressure and corresponding temperature drop in the shield flow. This cools the tip flow in the center tube, which prevents boiling and gas bubble formation in the helium, even at very low flow rates.  The helium is delivered at the sample end with the desired temperature stability and low vibrations.

Wired the Right Way - Your Way
Thermally Anchored Sensor Wiring on the DE-202 Cold Tip

Our technicians painstakingly wrap each cold head for optimum thermal anchoring. We offer you the choice of a variety of wiring options, from our standard offerings of single strand copper and low noise coaxial wiring packages to any number of custom wiring configurations.

Typical instrumentation for temperature measurement and control include one 36 ohm thermofoil heater, one curve matched silicon diode for rough temperature control, and one free length calibrated diode for direct attachment to the sample or sample holder for accurate temperature measurement. Silicon diode sensors are favored heavily for most standard applications because of their low cost, durability, and stability, but we do offer a wide variety of other sensors for different applications such as Cernox sensors for high magnetic fields, E-type thermocouples for 4 K-800 K measurements, and platinum RTDs for accurate high temperature measurements.

Our wide selection of wiring and instrumentation is matched by an equally wide selection of temperature controllers from Cryocon, Lake Shore, and Scientific Instruments.

LT3-OM Specifications

Cooling Technology-
  LT3-OM Open Cycle Cryocooler
  Refrigeration Type Liquid Helium Flow
  Liquid Cryogen Usage Helium, Liquid Nitrogen Compatible
Temperature*-
  LT3-OM < 4.2 K - 350 K ( < 2 K with pumping)
  With 800 K Interface (Base Temp + 2 K) - 700 K
  With 450 K Interface (Base Temp + 2 K) - 450 K
  Stability 0.1 K
  *Based on bare cold head with a closed radiation shield, and no additional sources of experimental or parasitic heat load.
Sample space-
  Diameter 19 mm (0.75 in)
  Height 0 - 3 mm ( 0 - 0.12 in)
  Sample Holder Attachment 1/4-28 screw
  Sample Holder View our Sample Holder Collection
Optical Access-
  Window Ports 1 ( 2 with transmission option )
  Diameter 25.4 mm (1 in)
  Clear view 23 mm (0.9 in)
  #/F Variable
  Window Material View our Wide Selection of Window Materials
Temperature Instrumentation and Control (Standard)-
  Heater 1 - 36ohm Thermofoil Heater Anchored on Cold Tip
  Control Sensor 1 - Curve Matched Silicon Diode
  Sample Sensor 1 - Calibrated Silicon Diode
  Custom Instrumentation Contact ARS for available Options
Instrumentation Access-
  Instrumentation Skirt Bolt-on, Stainless Steel
  Instrumentation Ports 1
  Instrumentation Wiring Contact our sales staff for wiring options
Vacuum Shroud-
  Material Stainless Steel
  Length 127 mm (5 in)
  Diameter 127 mm (5 in) (at the sample space)
  Width 38.7 mm (1.52 in) (at the sample space)
Radiation Shield-
  Material OFHC Copper, Nickel Plated
  Attachment Bolt on
  Optical Access 1 or 2(customer specified)
Cryostat Footprint-
  Overall Length 562 mm (22.12 in)
LT3-OM Sample Vibrations-
  X-Axis +/- 5-10 nm
  Y-Axis +/- 5-10 nm
  Z-Axis +/- 5-10 nm

LT3-OM Drift and Vibration Levels (X, Y, & Z Axis)

Liquid Helium Flow Cryostat Specifications

Cryostat Model LT3
   Cryogen Liquid helium Liquid nitrogen
   Base Temperature 4.2 K < 2 K with pumping 77 K
   Nominal Helium Consumption at 4.2 K 0.7 LL/hr  
    Cooling Capacity- 0.7 LL/hr 2 LL/hr  
  4.2 K 0.5 W 1.5 W  
  20 K 3.0 W 8.0 W  
  50 K 7 W 20 W  
    Maximum Temperature 450K with cold gas flow through transfer line  
    Cooldown Time- 4.2 K 20 min  
    Weight 0.9 kg (2 lbs)
LT3-OM Assembly Drawing

LT3-OM
Optical Microscopy Cryostat

Click on the images for full size.


LT-3B and LT-3OM

The cryostat on the left is a liquid helium cold cryostat for optical microscopy with adaptations for mounting and thermally anchoring a diamond anvil cell. The one on the right is a liquid helium cooled cryostat for FTIR and THZ applications featuring a 10 mm CVD diamond window, spectrometer adapter flange, and Z-translator for three sample measurement.