Optical Johnson noise thermometry

• US 5,098,197 A
• Filed: 01/30/1989
• Issued: 03/24/1992
• Est. Priority Date: 01/30/1989
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Department Of Energy
• Original Assignee: United States Department of Energy
• Inventors: Roberts, Michael J., Maxey, Lonnie C., Shepard, Robert L., Blalock, Theron V.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): WORTH, WILLIE M
• Application Number:
  US07/303,181
• Time in Patent Office: 1,149 Days
• Field of Search: 374/120, 374/5, 374/9, 374/121, 374/130, 374/131, 374/175, 374/122, 356/43, 324/244.1, 364/557, 364/574
• US Class Current: 374/120
• CPC Class Codes: G01J 2005/066 Differential arrangement, i.e. sensitive/not sensitive
• CPC Class Codes: G01J 5/0003 for sensing the radiant heat transfer of samples, e.g. emittance meter
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0802 Optical filters
• CPC Class Codes: G01J 5/0896 using a light source, e.g. for illuminating a surface

Abstract

Method and device for direct, non-contact temperature measure of a body. A laser beam is reflected from the surface of the body and detected along with the Planck radiation. The detected signal is analyzed using signal correlation technique to generate an output signal proportional to the Johnson noise introduced into the reflected laser beam as a direct measure of the absolute temperature of the body.

Claims

1. A method for non-contact measurement of the temperature of a body, comprising the steps of:

directing a laser beam onto the surface of said body to produce a reflected portion of said beam which includes an optical Johnson thermal noise modulation component produced by the interaction of said laser beam with the temperature dependent random motion of conduction band electrons at the surface of said body; and

analyzing said reflected portion of the laser beam from said body to measure the Johnson thermal noise modulation of the reflected portion of the laser beam from said body as a direct indication of the absolute temperature of said body.

2. The method as set forth in claim 1 further including the step of passing said reflected portion of said laser beam through a band-pass optical filter having a narrow bandwidth centered about the wavelength of said laser beam.

3. The method as set forth in claim 2 wherein said laser beam is a Helium-Neon laser beam having a wavelength of 632.8 nanometers and a beam power of about 3 milliwatts.

4. A device for non-contact measurement of the temperature of a body, comprising:

a laser for producing a Laser beam of a selected optical wavelength;

means for directing at least a portion of said laser beam onto said body to produce a reflected portion of said beam which includes an optical Johnson thermal noise modulation component produced by the interaction of said laser beam with the temperature dependent random motion of conduction band electrons at the surface of said body;

optical detecting means disposed to detect the reflected portion of the laser beam from said body and generating an output signal corresponding thereto; and

an analyzing means responsive to the output of said optical detecting means for generating an output signal proportional to the noise content of the signal corresponding to Johnson thermal noise modulation of the reflected portion of said laser beam as a direct indication of the absolute temperature of the body.

5. A method for non-contact measurement of the temperature of a body comprising the steps of:

directing a portion of a laser beam of a selected optical wavelength onto said body to produce a reflected beam which includes an optical Johnson noise modulation component produced by the interaction of said laser beam with the temperature dependent random motion of conduction band electrons at the surface of said body;

detecting portions of said reflected beam and incident portions of said laser beam at first and second pairs of optical detectors, respectively, and generating corresponding first and second pairs of analog electrical signals at corresponding outputs thereof;

analyzing said first and second pairs of analog electrical signals by corresponding first and second analog signal subtraction circuit means for generating first and second difference signals corresponding to the difference in said first and second pairs of analog electrical signals applied to the respective inputs thereof; and

correlating said first and second difference signals to generate an output signal proportional to the correlated signal content thereof indicative of the Johnson thermal noise component of aid reflected beam as a direct indication of the absolute temperature of said body.

6. A device for non-contact measurement of the temperature of a body, comprising:

a laser for producing a laser beam of a selected optical wavelength;

means for directing at least a portion of said laser beam onto said body to produce a reflected portion of said beam which includes an optical Johnson noise modulation component produced by the interaction of said laser beam with the temperature dependent random motion of conduction band electrons at the surface of said body;

first and second pairs of optical detectors, each pair of said optical detectors disposed to detect a portion of said reflected beam from said body at one detector and an incident portion of said laser beam at the other of said pair of detectors and generating first and second analog electrical signals corresponding thereto; and

an analyzing circuit including first and second analog signal subtraction circuit means responsive to separate ones of said first and second pairs of analog electrical signals for generating first and second difference signals corresponding to the difference in said first and second pairs of analog electrical signals applied to inputs thereof and a correlation circuit means having first and second inputs responsive to said first and second difference signals for generating an output signal proportional to the correlated signal content of said first and second difference signals indicative of the Johnson thermal noise component of said reflected beam as a direct indication of the absolute temperature of said body.

7. The device as set forth in claim 6 wherein each of said first and second analog signal subtraction circuit means includes a differential amplifier having first and second input connected to receive corresponding ones of said outputs from said first and second pairs of optical detectors, respectively, and an output.

8. The device as set forth in claim 6 further including a band-pass optical filter having a narrow bandwidth centered about the wavelength of said laser beam and disposed in the path of said reflected portion of said laser beam.

9. The device as set forth inn claim 8 wherein said laser is a helium-neon laser having an output of about 3 milliwatts and tuned to a wavelength of about 632.8 nanometers.