## 3 Results and Discussion
The waveforms obtained after this procedure are shown in Figure 7b. The calibration of the absorption coefficient measurements corresponding to the black curve amplitude minus this influence gave a value equal to 5.6 \(\times\) 10\({}^{-7}\) cm\({}^{-1}\). If we use an estimate of the magnitude of the 7.8 \(\times\) 10\({}^{-8}\) cm\({}^{-1}\) correction introduced by the mirrors, we obtain a more realistic value of 6.4 \(\times\) 10\({}^{-7}\) cm\({}^{-1}\). The colored curves correspond to the waveforms obtained at different positions of the crystal. The maximum absorption coefficient measured in this series of experiments was 4 \(\times\) 10\({}^{-6}\) cm\({}^{-1}\). It should be noted that the minimum absorption coefficient found after purposeful studies of this sample was 2.5 \(\times\) 10\({}^{-7}\) cm\({}^{-1}\). Figure 7c shows the same waveforms normalized to their maximum amplitude. It is well seen that their forms are different. Especially distinctive is the difference in the rate of decline of the curves in the cooling area after the end of the heating pulse. This clearly indicates the presence of an additional contribution to the measurements not related to crystal absorption, since the signal changes caused by its absorption occur at shorter time frames [14]. Next, we separated this contribution by digital processing of the obtained waveforms. First of all, it is obvious that if this contribution does not change when moving the crystal, then the difference of the obtained waveforms should be similar to a uniform form for all waveforms. Figure 8a shows the differences of the waveforms obtained at different sample positions and the waveform obtained at the position with minimal absorption (Figure 7a, black positive curve). Figure 8b shows the same curves normalized to their maximum amplitudes. One can see the similarity of these curves within the accuracy of the measurements. They can be used to construct a universal curve representing the influence of the crystal heating and cooling process on the observed signal. For reasons of greater accuracy, it is necessary to subtract the waveform with minimum amplitude from the waveform with maximum amplitude and normalize the obtained curve by its amplitude. Such a curve (light blue) is shown in Figure 8b among other curves. With the help of the universal curve obtained in this way it is possible to determine the distortion of an arbitrary waveform associated with external disturbances. Figure 8c shows two characteristic curves, which are the difference between the curves shown in Figure 7b and the universal curve with the matched amplitude. The criterion for choosing the amplitude of the universal curve was the coincidence of the obtained difference with the measured temporal contribution of elements M\({}_{2}\) and M\({}_{3}\) (Figure 6b) during the heating interval. The black curve in Figure 8c is a piecewise linear approximation of the curves corresponding to the thermal influence of these elements. The given waveforms processing shows that the difference of these waveforms from the universal curve is of a regular nature over the time interval of the heating pulse. This allows us to use the values of this difference as a correction to the measured waveforms. It can also be concluded that the refractive index of the sample has a weak influence on the distortions introduced by the mirror M\({}_{3}\). Therefore, the studies have shown that in case of the replacement of the optical elements M\({}_{2}\) and M\({}_{3}\) with better ones in terms of their thermal influence on the measurements, the sensitivity of the described scheme (defined as absorption giving a signal equal to the root mean square value of the noise component) for measurements of the absorption coefficient in crystalline quartz will be \(\sim\)10\({}^{-8}\) cm\({}^{-1}\). This conclusion also applies to the case of application of the above-described procedure of making a correction to the values of the measured absorption coefficients.