We have found some errors in the piezo-optic coefficients measured for ${\mathrm{LiKB}}_4{\mathrm{O}}_7$, ${\mathrm{Li}}_2{\mathrm{B}}_6{\mathrm{O}}_{10}$, and ${\mathrm{LiCsB}}_6{\mathrm{O}}_{10}$ glasses in our recent work [1]. The errors arose because a common uniaxial mechanical loading method was applied, leading to the appearance of spatially inhomogeneous stresses inside the glass samples, with unknown coordinate dependences (see, e.g., Ref. [2]). As a result, the stress tensor components and, subsequently, the piezo-optic coefficients were determined with inappropriate errors or even incorrectly. In addition, the contribution of Poisson strain to the total optical retardation determined with the interferometric technique was not accounted for in Ref. [1].

We have reinvestigated the piezo-optic coefficients for ${\mathrm{LiKB}}_4{\mathrm{O}}_7$, ${\mathrm{Li}}_2{\mathrm{B}}_6{\mathrm{O}}_{10}$, and ${\mathrm{LiCsB}}_6{\mathrm{O}}_{10}$ glasses using an experimental method suggested recently. It is based on a so-called four-point bending technique [3]. The correct piezo-optic coefficients have been obtained, as shown in Table 1. Table 1 also presents the recalculated photoelastic coefficients. Moreover, we have introduced the corrections for the mean-square deviations for the elastic stiffness coefficients.

Table 1. Acoustic, Piezo-Optic, Elastic, Photoelastic, and Acousto-Optic Parameters of the Borate Glasses

View Table

It follows from the results of our recent work [4] that the optically isotropic glass media are characterized by three different types of acousto-optic (AO) figures of merit and not four as supposed in Ref. [1]. They are concerned with the following experimental geometries:

Notice that a fourth, hypothetical, type of AO interaction has also been considered in Ref. [1]. It involves a transverse acoustic wave $v_{13}$ and an incident optical wave polarized parallel to the $Y$ axis. However, this interaction cannot be implemented since the relevant elasto-optic coefficient $p_{25}$ is equal to zero in all isotropic solid-state media (see Ref. [4]).

The AO figures of merit for all of the three possible types of AO interactions may be written as, $M_2^{(\mathrm{I})}=n^6{p}_{12}^2/\rho v_{11}^3$, $M_2^{(\mathrm{II})}=n^6{(p_{12}{\sin }^2{\theta }_B+p_{11}{\cos }^2{\theta }_B)}^2/\rho v_{11}^3$, and $M_2^{(\mathrm{III})}=n^6{(p_{44}{\sin }^2{\theta }_B)}^2/\rho v_{13}^3$ (see Ref. [4]), where $p_{44}=p_{11}-p_{12}$, $p_{11}$, and $p_{12}$ are the photoelastic coefficients, $v_{11}$ and $v_{13}$ are the velocities of the longitudinal and transverse acoustic waves, respectively, $n$ denotes the refractive index, $\rho$ is the glass density, and ${\theta }_B$ is the Bragg angle defined by the relation $\sin {\theta }_B=\lambda f_a/2{nv}_{ij}$. Here, the acoustic wave frequency $f_a$ takes a value of 500 MHz.

The corrected values of the AO figures of merit are gathered in Table 1. Among the borate glasses under analysis, the highest AO figure of merit corresponds to ${\mathrm{LiCsB}}_6{\mathrm{O}}_{10}$. It is equal to $(7.443\pm 0.529)\times {10}^{-15}{\mathrm{s}}^3/\mathrm{kg}$ rather than, $(201\pm 104)\times {10}^{-15}{\mathrm{s}}^3/\mathrm{kg}$ as declared in Ref. [1]. Nonetheless, the ${\mathrm{LiCsB}}_6{\mathrm{O}}_{10}$ glass still remains an effective AO material, in compliance with what has been concluded in Ref. [1].