The holmium laser, which operates in a wavelength of 2.1 microns, is highly absorbed by water and has a shallow penetration depth of approximately 0.4 mm. As a pulsed mode laser, the Holmium reduces deeper thermal effects and charring which are more prevalent in Continues Wave lasers (e.g. Thulium, KTP).
In statistical theory, covariance is a measure of how much two random variables change together. In other words, covariance is a measure of the strength of the correlation between two random variables. Also, it can be considered as a generalization of the concept of variance of two random variables.
The sampling estimator of Â¾ (x;y) is similar in formto that for a variance,Cov(x;y)= n (xy Â¡ x Â¢ y) n Â¡1(3.9)where n is the number of pairs of observations, and xy =1 n X ni =1 x i y i The covariance is a measure of association between x and y (Figure 3.1).