Optical temperature sensor using speckle field

• Development of a simple and compact temperature sensor based on speckle correlation is described.
• Laser speckle pattern produced by a metal plate is used to measure the temperature changes.
• Change in speckle correlation is related to the temperature change.
• The main advantage of the technique is that it can be used for remote monitoring of temperature in a minimally invasive manner.

This paper presents a newly developed, laserbased, noncontact and remote temperature sensor suitable for high as well as low temperature measurements, which can be adapted to a commercial tensile testing machine equipped with an electrical furnace to monitor temperature. It can also be a miniaturized sensor for remote measurement of body temperature for biomedical diagnostics (e.g. as a sensor integrated into an endoscope to measure internal temperature during surgical procedure). The basic principle of the sensor is based on determining the changes occurring to a secondary speckle pattern generated by the scattered laser beam from a rough surface. In the present case a rough metal surface is used. As the surface of the metal plate changes due to cantilever action when exposed to heat, the resulting speckle pattern also changes. This change in the speckle pattern is computed by comparing it to a reference speckle pattern recorded at known temperature and can so be related to the temperature change. From the value of correlation coefficient we were able to measure the temperature. Furthermore, the paper presents the description of the signal processing algorithm and the optical arrangement. Based on the experimental data, it can be shown that this sensor can be successfully used for the remote extraction of temperature.