“…(1) and (3) to (5), we obtain the following expressions: The signs of A, to A, cannot be determined from intensity measurements. They are, however, uniquely defined by (4) and (6) to (9) if one takes the square roots as positive. Taking a to be negative [18] and the known values of the elasto-optic constants, we obtain the magnitudes and signs of A,, A,, A,, and A, given in Table 1.…”