Cryogenic thermometer employing molecular luminescence

A method of maintaining a constant cryogenic temperature of an environment, the method comprising:

• placing a sensor material in said environment and allowing said sensor material to have its temperature be the same as said cryogenic temperature, said sensor material having an excited multiplet state which has a higher energy sublevel state and a lower energy sublevel state, said sensor material having a capability of emitting radiant emissions in the visible or near infrared spectral region from both of the sublevel states when said sensor material is excited, said sublevel states being split by an energy separation in the absence of electric or magnetic fields (zero field splitting), and said zero field splitting being sufficiently great that the radiant emissions from the two said sublevel states are optically resolvable from each other, the radiant emissions from said sublevel states each having a degree of intensity,
• exciting said sensor material to cause both of said sublevel states of said multiplet state to emit radient emission,
• detecting separately the degrees of intensity of the radiant emissions from said sublevel states,
• determining a relationship between the detected degrees of intensity of the radiant emissions from said sublevel states, and
• heating or cooling said environment as needed to maintain said relationship at a constant level.

Apparatus for measuring a cryogenic temperature of an environment, the method comprising:

• sensor material adapted to be placed in said environment so that its temperature can be the same as said cryogenic temperature, said sensor material having an excited multiplet state which has a higher energy sublevel state and a lower energy sublevel state, said sensor material having a capability of emitting radiant emissions in the visible or near infrared spectral region from both of the sublevel states when said sensor material is excited, said sublevel states being split by an energy separation in the absence of electric or magnetic fields (zero field splitting), and said zero field splitting being sufficiently great that the radiant emissions from said sublevel states are optically resolvable from each other, the radiant emissions from said sublevel states each having a degree of intensity,
• means for exciting said sensor material to cause both of said sublevel states of said multiplet state to emit radiant emission,
• means for generating first and second signals proportional to the degrees of intensity of the radiant emissions from said higher energy and lower energy sublevel states, respectively,
• means for calculating the temperature of said sensor material from a ratio of said first and second signals.

Apparatus for maintaining a constant cryogenic temperature of an environment comprising:

• a sensor material adapted to be placed in said environment so that its temperature can be the same as said cryogenic temperature, said sensor material having an excited multiplet state which has a higher energy sublevel state and a lower energy sublevel state, said sensor material having a capability of emitting radiant emissions in the visible or near infrared spectral region from both of the sublevel states when sand sensor material is excited, said sublevel sates being split by an energy separation in the absence of electric or magnetic fields (zero field splitting), and said zero field splitting being sufficiently great that the radiant emissions from said sublevel states are optically resolvable from each other, the radiant emissions from said sublevel states each having a degree of intensity,
• means for generating first and second signals proportional to the degrees of intensity of the emitted radiations from said higher energy and lower energy sublevel states, respectively,
• means for determining a ratio of said first and second signals,
• means for heating or cooling said environment, and
• feedback means for actuating said heating or cooling means in response to a variation of the ratio of said first and second signals from a desired value to heat or cool said environment as needed to thereby heat or cool said sensor material and cause said ratio of said first and second signals to return to said desired value.