Intensity broadening of internally reflected laser beam from a meniscus formed in a capillary pore—applied for automated liquid column height measurements

An automated liquid column height measurement technique using the total internal reflection of a collimated laser beam from the convex meniscus surface is proposed. This new technique can alleviate the shortcomings of the traditional cathetometer that tends to introduce user bias. Experimental measurements and theoretical predictions have been conducted to examine the detected signal broadening and measurement uncertainties of the proposed technique, resulting from (1) the finite laser-beam diameter, (2) the capillary pore diameter, (3) the beam steering by thermal gradients, and (4) the beam steering by density variations of the liquid inside a capillary pore. For the collimated 52.6-lm diameter laser beam, for three different tested pores of 0.5, 1.0, and 2.0 mm diameter, the overall uncertainty of the wicking height measurement is estimated to be ±12 lm in the case of on-axis detection, and ±24 lm in the case of off-axis detection.