Thermo-optic coefficient measurement systems
A thermo-optic coefficient measurement system can include a housing structure configured to retain at least a first plate sample, a second plate sample, and a third plate sample in a stacked, alternating stagger arrangement such that a gap exists between the first plate sample and the third plate sample that is the thickness of the second plate sample. The system can also include a first optical device connected to the housing to output a first laser configured to be coincident with the first plate sample and the third plate sample. The first optical device can be configured to receive a first return signal. The system can also include a second optical device connected to the housing to output a second laser configured to be coincident with the second plate sample, the second optical device can be configured to receive a second return signal. The system can include an optical interrogator module configured to be connected to the first optical device to output the first laser thereto and to receive the first return signal therefrom. The optical interrogator module can be configured to be connected to the second optical device to output the second laser thereto and to receive the second return signal therefrom. The optical interrogator module can be configured to determine a thermo-optical coefficient as a function of the first return signal and the second return signal at a plurality of temperatures.
1 . A thermo-optic coefficient measurement system, comprising:
a housing structure configured to retain at least a first plate sample, a second plate sample, and a third plate sample in a stacked, alternating stagger arrangement such that:
a first gap exists between the first plate sample and the third plate sample that is the thickness of the second plate sample; and
a portion of the second plate sample forms an overhang that extends past outer edges of the first plate and the second plate, such that a second gap exists between the housing and the portion of the second plate sample;
a first optical device connected to the housing to output a first laser configured to be coincident with the first plate sample, the third plate sample, and the first gap, the first optical device configured to receive a first return signal;
a second optical device connected to the housing to output a second laser configured to be coincident with the portion of the second plate sample that forms the overhang, such that the second laser is oriented so as to pass through the overhang portion of the second plate but through neither the first plate nor the third plate, the second optical device configured to receive a second return signal; and
an optical interrogator module configured to be connected to the first optical device to output the first laser thereto and to receive the first return signal therefrom, the optical interrogator configured to be connected to the second optical device to output the second laser thereto and to receive the second return signal therefrom, wherein the optical interrogator module is configured to determine a thermo-optical coefficient as a function of the first return signal and the second return signal at a plurality of temperatures.
2 . The system of claim 1 , wherein the thermo-optical interrogator module is configured to determine optical coefficient as a function of harmonic wavelengths of the first return signal and the second return signal.
3 . The system of claim 1 , wherein the first laser is configured to sense a change in optical path between a rear surface of the first plate sample and a front surface of the third plate sample as a function of temperature, wherein the second laser is configured to sense a change in optical path between a front surface of the second plate sample and a rear surface of a second plate sample as a function of temperature, and wherein the optical interrogator module is configured to cancel out temperature induced effects due to optical path change of the second plate sample by comparing the first return signal to the second return signal resulting in determining effects on the second plate sample due only to thermo-optic effect.
4 . The system of claim 1 , further comprising the first, second, and third plate samples.
5 . The system of claim 4 , wherein the first optical device abuts the first plate sample.
6 . The system of claim 5 , wherein the second optical device is spaced from the second plate sample, wherein the first and third plate samples are outside a cone of influence of the second optical device.
7 . The system of claim 6 , wherein the housing includes one or more portions configured to sandwich the first, second, and third plate samples together without inducing stress effects on an optically relevant order of magnitude.
8 . The system of claim 1 , wherein the optical interrogator module is configured to determine index of refraction of the plate samples as a function of the ratio of a static optical path measurements of the first return signal and the second return signal taken at a fixed temperature.
9 . A method, comprising:
retaining a first plate sample, a second plate sample, and a third plate sample in a stacked, alternating stagger arrangement such that:
a first gap exists between the first plate sample and the third plate sample that is the thickness of the second plate sample; and
a portion of the second plate sample forms an overhang that extends past outer edges of the first plate and the third plate, such that a second gap exists between the housing and the portion of the second plate sample;
interrogating the first plate sample with a first laser coincident with the first plate sample, the third plate sample, and the first gap, and receiving a first return signal thereof at a plurality of temperatures, such that the first laser passes through the first plate sample and the third plate sample, but not the second plate sample;
interrogating the second plate sample with a second laser coincident with the portion of the second plate sample that forms the overhang, and receiving a second return signal thereof at the plurality of temperatures, such that the second laser passes through the second plate sample but neither the first nor the third plate samples; and
determining a thermo-optical coefficient as a function of the first return signal and the second return signal at the plurality of temperatures.
10 . The method of claim 9 , wherein determining the thermo-optical coefficient includes using harmonic wavelengths of the first return signal and the second return signal.
11 . The method of claim 9 , wherein determining the thermo-optical coefficient includes cancelling out temperature induced effects due to optical path change of the second plate sample by comparing the first return signal to the second return signal resulting in determining effects on the second plate sample due only to thermo-optic effect.
12 . The method of claim 11 , wherein retaining the plate samples includes abutting the first plate sample to a first optical device.
13 . The method of claim 12 , wherein retaining the plate samples includes spacing second plate sample from a second optical device, wherein the first and third plate samples are outside a cone of influence of the second optical device.
14 . The method of claim 12 , wherein retaining the plate samples includes sandwiching the first, second, and third plate samples together without inducing stress effects on an optically relevant order of magnitude.
15 . The method of claim 12 , further comprising holding temperature fixed and determining an index of refraction of the plate samples as a function of the ratio of a static optical path measurements of the first return signal and the second return signal taken at the fixed temperature.