The stiffness measurement precision of an optical trap is a key in optical force measurement
so this paper proposes a method based on Boltzmann statistics to analyze the stiffness measurement precision of the optical trap. Firstly
a near infrared optical tweezer was introduced and it was built on an air cushion platform in a dark room to isolate light interference and vibration interference. Then
a quadrant photodiode was used to detect the backscatter light of a microsphere captured by the tweezer and the Boltzmann statistics method having no relation with solution viscosity was adopted to calculate the optical trap stiffness near the bottom surface of the sample cell. Finally
the influences of the solution temperature
the sensitivity of the quadrant photodiode
sampling frequency
and the sampling time on the accuracy of the optical trap stiffness measurement were analyzed and discussed. Theoretical analysis and practical calculation results indicate that the solution temperature has a little effect on the measurement
but the sensitivity of the quadrant photodiode influences on the measurement precision greatly. In consideration of complete sampling and higher data processing speeds
the sampling frequency is set 5 to 10 times as great as the knee frequency of the optically trapped microsphere. For the measurement setup proposed in this paper
the sampling time is set in the range 1-7 s
which ensures the higher measurement precision of the optical trap.
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references
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