Abstract:
A low temperature cryostat is disclosed. The low temperature cryostat may include a cryostat vessel, a cooling device arranged in the cryostat vessel for producing a cooling temperature level, a microscopy device for examining a sample, and at least one thermal coupling for thermally and mechanically connecting the microscopy device to the cooling device. The cooling device may comprise a pulse tube cooling system.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application claims priority to Patent Cooperation Treaty Application Number PCT/EP2005/056316 filed Nov. 29, 2005, which claims priority to German Application DE 20 2004 018 469.9 filed Nov. 29, 2004, both of which contents are incorporated herein by reference. 
     
    
     NOTICE OF COPYRIGHTS AND TRADE DRESS 
       [0002]    A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become trade dress of the owner. The copyright and trade dress owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright and trade dress rights whatsoever. 
       BACKGROUND 
       [0003]    1. Field 
         [0004]    This disclosure relates to a low temperature cryostat. 
         [0005]    2. Description of the Related Art 
         [0006]    It is conventional to make use in low temperature microscopy of sample tubes in which the respective microscope is arranged. The sample tubes are inserted into 4K cryostats and cooled by means of liquid nitrogen (77K) and liquid helium (4K). A so-called dipstick with a sample to be examined and a microscope is inserted into the sample tube and cooled. The sample tube itself can in this case be evacuated or be filled with exchange gas for the purpose of better thermal coupling to the liquid nitrogen and the liquid helium. 
         [0007]      FIG. 6  shows such a conventional arrangement having a cryostat vessel  302  that is evacuated. A cooling device  304  and a microscopy device  306  are arranged in the cryostat vessel  302 . The cooling device  304  comprises a nitrogen cooler  310  with liquid nitrogen as coolant. The nitrogen cooler  310  is connected to a 70K cold shield  314  via a thermal 70K coupling  312 . Arranged concentrically in the nitrogen cooler  310  with 70K cold shield  314  is a helium cooler  320  that is thermally coupled to a 4K cold shield  324  via a 4K coupling  322 . A sample tube  330  is arranged concentrically relative to the helium cooler  320  with 4K cold shield  322 , and relative to the nitrogen cooler  310  with 70K cold shield  314 . The thermal connection between the sample tube  330  and the nitrogen cooler  310  and/or the helium cooler  320  is performed by a mechanical, and therefore thermal connection of the sample tube  330  to the 70K coupling  314  and/or the 4K coupling  324 . A sample rod or dipstick  332  is inserted into the sample tube  330 , and a confocal microscope  334  is arranged at its lower end. 
         [0008]    Cooling with the aid of liquid nitrogen and liquid helium is disadvantageous in this known apparatus, since handling liquid nitrogen and liquid helium is complicated and awkward. Moreover, the use of liquid helium is expensive. 
         [0009]    It is therefore an object of the present invention to specify a low temperature cryostat that is easier to handle and more cost-effective in operation. 
         [0010]    This object is achieved by means of a low temperature cryostat in accordance with the features of claim  1 . 
         [0011]    Further details, features and advantages of the invention emerge from the following description of preferred embodiments of the invention with the aid of the drawings, in which: 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a schematic of a first embodiment of the invention having a single-stage pulse tube cooler; 
           [0013]      FIG. 2  shows a second embodiment of the invention having a two-stage pulse tube cooler; 
           [0014]      FIG. 3  shows a detailed illustration of the confocal microscope of the second embodiment of the invention having a piezo positioning apparatus; 
           [0015]      FIG. 4  shows a detailed illustration, corresponding to  FIG. 3 , of a third embodiment of the invention having an atomic force or scanning tunneling microscope instead of the confocal microscope; 
           [0016]      FIG. 5  shows a fourth embodiment of the invention having a ADR cooling stage, a 100 mK cooling stage and a confocal microscope; 
           [0017]      FIG. 6  shows a low temperature cryostat according to the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods disclosed or claimed. 
         [0019]    Since it is impermissible in low temperature microscopy to transmit vibrations onto the sample, there has so far been no use of mechanical cooling devices such as compressors and pulse tube coolers. Compressor cooling devices have a broad spectrum of vibrations from the low frequency up to the high frequency range, and are therefore unsuitable as a replacement for nitrogen/helium coolers. Given appropriate design, pulse tube coolers can certainly be configured because of vibration, but their functionality dictates that they have vibrations in the low frequency  1  Hz range that cannot be eliminated. These vibrations originate from the oscillating gas column in the pulse tube cooler. These vibrations cause a deflection of the cold head of the pulse tube cooler in the □m region. The use of pulse tube coolers has so far been refrained from because of these vibrations that cannot be eliminated. However, it has been shown that when use is made of pulse tube coolers these low frequency vibrations are by far less disturbing than assumed. This is likely to be ascribed to the fact that the microscope device connected to the cold head covibrates synchronously because of the low frequencies, and this oscillation is therefore not disturbing. 
         [0020]    In accordance with an advantageous refinement of the invention, the component of a pulse tube cooler that still most readily also generates high frequency vibrations in addition to the low frequency vibrations, specifically the turning valve, is arranged outside the cryostat vessel and is connected to the latter by means of a flexible hose line. This prevents the high frequency vibrations from impairing the mode of operation of the microscopy device, and at the same time the low frequency vibrations are reduced. Consequently, it is only the low frequency vibrations that still occur in the cryostat vessel on the basis of the oscillating gas. 
         [0021]    In accordance with a further preferred refinement of the invention, the thermal coupling of the microscopy device to the pulse tube cooling system is designed in an elastic and vibration damping fashion. Consequently, the low frequency vibrations still occurring from the pulse tube cooling system are strongly damped and are therefore less able to have a disturbing effect on the microscopy device. Moreover, account is thereby taken of the unavoidable changes in length between ambient temperature and the temperature of the sample. 
         [0022]    Such a low temperature cryostat can be used with a multiplicity of different microscopy devices such as confocal microscope, tunneling microscope, atomic force microscope, magnetic microscope, chemical microscope etc. 
         [0023]    The remaining subclaims relate to further advantageous refinements of the invention. 
         [0024]      FIG. 1  shows a schematic of the essential components of a first embodiment of the invention, in the case of which the basic concept of the invention is concerned. A cooling device  4  in the form of a single-stage pulse tube cooler  10  is arranged in a cryostat vessel  2 . The pulse tube cooler  10  comprises a pulse tube  12  and a regenerator  14  that are arranged between a cold head  16  and a valve head  18 . A microscopy device  6  is mechanically and thermally coupled to the cold head  16  by means of a thermal coupling  8 . 
         [0025]      FIG. 2  shows a second embodiment having a cryostat vessel  102 , a cooling device  104 , arranged in the cryostat vessel  102 , in the form of a two-stage pulse tube cooling system  110 . The pulse tube cooling system  110  has a first pulse tube cooler  111  and a second pulse tube cooler  121 . The first pulse tube cooler  111  has a first pulse tube  112  and a first regenerator  113 . The first pulse tube  112  and the first regenerator  113  are arranged between a valve head  114  and a 60K cold head  115 . The second pulse tube cooler  121  has a second pulse tube  122  and a second regenerator  123 . The second pulse tube  122  is arranged between the valve head  114  and a 4K cold head  125 , and the second regenerator  123  is arranged between the 60K cold head  115  and the 4K cold head  125 . A ballast volume  116  is directly connected to the valve head  114  arranged outside the cryostat vessel  102 . The valve head  114  and the ballast volume  116  are connected to a turning valve  118  via a flexible hose  117 . 
         [0026]    Arranged in the cryostat vessel  102  is a sample tube  130  that is accessible from the outside and into which a sample rod  132  can be inserted. The sample rod  132  has a warm end  134 , which projects from the cryostat vessel  102 , and a cold end  136 , which comes to lie in the interior of the cryostat vessel  102 . A confocal microscope  138  is arranged in the region of the cold end  136  of the sample rod  132 . 
         [0027]    The sample tube  130 , and thus the sample rod  132  with the confocal microscope  138  are connected thermally to the 60K cold head  115  via a 60K coupling  140 , and to the 4K cold head  125  of the cooling device  104  via a 4K coupling  142 . The 60K coupling  140  is arranged closer at the warm end  134 , and the 4K coupling  142  is arranged in the region of the cold end  136 . The sample rod  132  is arranged concentrically in the sample tube  130 . The sample tube  130  has a hollow cladding  144  that can be evacuated or filled with exchange gas. 
         [0028]    Owing to the spatially separated arrangement of the turning valve and its connection to the valve head via a flexible hose  117 , vibrations of the turning valve  118  are strongly damped, and scarcely any vibrations are transmitted onto the cryostat vessel. Owing to the configuration of the 60K coupling  140  and of the 4K coupling  142  in the form of an elastic strip made from material that effectively conducts heat, vibrations from the pulse tube cooling system are likewise strongly damped, and so scarcely any vibrations are transmitted onto the sample tube  130 , and thus onto the confocal microscope  138 . A braided ground strap made from electrolytic copper is well suited therefor. 
         [0029]      FIG. 3  shows a detail of the third embodiment of the invention, specifically the cold end  136  of the sample rod  132  with the confocal microscope  138 . The confocal microscope  138  comprises a lens arrangement  146  that is thermally and mechanically connected to the 4K coupling  142  by means of a piezo positioning apparatus  148 . A sample  150  to be examined is arranged below the lens arrangement  146 . The light that originates from a light source (not illustrated), is reflected by the sample  150  and falls into the lens arrangement  146  is guided out of the cryostat vessel  102  via an optical fiber  152 . The viewing light is preferably likewise coupled in via the optical fiber  152 . The focusing of the lens arrangement  146  is performed by the piezo apparatus  148 . The lens arrangement  146  can be moved and positioned on three spatial axes relative to the sample  150  with the aid of the piezo positioning apparatus  148 . The entire arrangement is surrounded by a cladding  154  that is part of the sample rod  132 . 
         [0030]      FIG. 4  shows a detail of a third embodiment of the invention, in the case of which instead of a confocal microscope an atomic force or scanning tunneling microscope  160  is provided in the cryostat design according to  FIG. 2 . Components are correspondingly provided with the same reference numerals in  FIGS. 3 and 4 . The third embodiment of the invention differs from the second embodiment only in that a carrier unit  162  for a scanning tip  164  is provided instead of the lens arrangement  146 , and an electric signal line  166  is provided instead of the light guide  152 . 
         [0031]      FIG. 5  shows a fourth embodiment of the invention having a cryostat vessel  202  in which a cooling device  204  is accommodated. The cooling device  204  arranged in the cryostat vessel  202  comprises a two-stage pulse tube cooling system  210  having a first pulse tube cooler  211  with a first cold head  215 , and a second pulse tube cooler  221  with a second cold head  225 . The interface to the outside is provided via a valve head  214 . The remaining components such as turning valve and ballast volume, for example, are not illustrated. The two-stage pulse tube cooling system  210  comes close to the pulse tube cooling system from  FIG. 2 . The two-stage pulse tube cooling system  210  precools an adiabatic demagnetization cooling stage or an ADR cooling stage  205 , having a magnet that is not, illustrated, to approximately 4K. The ADR stage  205  is thermally and mechanically coupled to the second cold head  225  of the two-stage pulse tube cooling system  210  The confocal microscope  238  with positioning apparatus (not illustrated) is arranged at the magnet (not illustrated) of the ADR cooling stage  205 . The confocal microscope  238  is thereby thermally coupled to the second cold head  225  and is cooled to approximately 4K. The ADR cooling stage  205  cools to approximately 100 mK. A sample  208  is thermally coupled to the ADR cooling stage  205  via a sample holder  206 , such that the sample is cooled to approximately 100 mK. 
         [0032]    The above-described embodiments of the invention may also be combined with one another. It is likewise possible, for example, to arrange a number of different microscopes in the cryostat vessel. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           2  Cryostat vessel 
           4  Cooling device 
           6  Microscopy device 
           8  Thermal coupling 
           10  Pulse tube cooler 
           12  Pulse tube 
           14  Regenerator 
           16  Cold head 
           18  Valve head 
           102  Cryostat vessel 
           104  Cooling device 
           110  Two-stage pulse tube cooling system 
           111  First pulse tube cooler 
           112  First pulse tube 
           113  First regenerator 
           114  Valve head 
           115  60K cold head 
           116  Ballast volume 
           117  Flexible hose 
           118  Turning valve 
           121  Second pulse tube cooler 
           122  Second pulse tube 
           123  Second regenerator 
           125  4K cold head 
           130  Sample tube 
           132  Sample rod 
           134  Warm end of  132   
           136  Cold end of  132   
           138  Confocal microscope 
           140  60K coupling 
           142  4K coupling 
           144  Cladding of  130   
           146  Lens arrangement 
           148  Piezo apparatus 
           150  Sample 
           152  Optical fiber 
           160  AFM or scanning tunneling microscope 
           162  Carrier unit for  164   
           164  Scanning tip 
           166  Electric signal line 
           202  Cryostat vessel 
           204  Cooling device 
           205  ADR cooling stage 
           206  Sample holder 
           208  Sample 
           210  Two-stage pulse tube cooling system 
           211  First pulse tube cooler 
           214  Valve head 
           215  First cold head 
           221  Second pulse tube cooler 
           225  Second cold head 
           238  Confocal microscope 
           302  Cryostat vessel 
           304  Cooling device 
           306  Microscopy device 
           310  Nitrogen cooler 
           312  70K coupling 
           314  70K cold shield 
           320  Helium cooler 
           322  4K coupling 
           324  4K cold shield 
           330  Sample tube 
           332  Sample rod (dipstick) 
         Closing Comments 
       
     
         [0097]    The foregoing is merely illustrative and not limiting, having been presented by way of example only. Although examples have been shown and described, it will be apparent to those having ordinary skill in the art that changes, modifications, and/or alterations may be made.