## 1 Introduction
Although oil is commonly used as an immersion medium, there are also experiments using water immersion objectives [19]; experimental conditions determine whether one or the other is chosen [20]. Regarding the influence of an immersion medium in an optical trap, it has previously been reported how the optical excitation of oil can influence the change in the trap focal length [21], and the same effect has been proven by testing immersion oils of different refractive indexes [22]. It has also been reported that by combining a confocal microscope and an optical trap, when using independent laser sources that share the same immersion objective, the change in the optical trap laser power changes the confocal focus position [23; 24]. The variation in the beam convergence geometry has been considered as an effect on fluid pressure [25], as well as a change in the quantum state of the matter and radiation [13], and even the thermal effects of this convergence that are induced by modulation in radiation power have been characterized [26]. However, to the knowledge of the authors of this work, no reports have been found in the literature that suggest a change in the laser beam power of an optical trap generates any change in the phase of the wavefronts that are transmitted by the optical elements of the same trap. In this work, a conventional optical trap is combined with a Mach-Zehnder interferometer, where independent laser sources that share several optical components are used. Among the shared elements is the oil immersion objective, which generates the optical trap; in Section 2, the systems are described separately, followed by their coupled implementation. In preliminary experiments, it was detected that upon changing the power of either one of the two laser sources, the interferograms showed an additive phase shift; the cause and mechanism of this effect were unknown at the time. This manuscript presents a methodology to measure and correct the contribution of such additive phase, due to some component from the optical tweezers or the interferometer, discarding the possibility that it could be due to a direct contribution of the sample under study. In Section 3 of this work, we first describe the method implemented to identify the contribution that each experimental arrangement component in common could have on the phase shifting observed; our experimental results have allowed us to determine that the phase shifting is caused by the oil immersion microscope objective. Consequently, a study of the optical, thermal, and morphological behavior of the oil implemented on a macroscopic scale outside the trap-interferometer setup and exciting it with a higher power laser is shown below. The foregoing is also due to the fact that within the trap-interferometer setup it is not possible to individually analyze the oil characteristics. Although this analysis allows an understanding of the general behavior of immersion oil, the particular calibration on the optical trap must be implemented in situ, as indicated below. Finally, in Section 4, we present the phase calibration to be performed on interferometer measurements when a change in laser source power is involved. In this case, the optical trap is used to generate deformations on a black paint film at different powers, while interferometry is used to measure the deformation due to thermal stress applied by the optical trap. Since the change in trap laser power adds a phase shifting to the interferograms that measure the deformation, it is necessary to calibrate this additive phase term in the trap-interferometer system, to subsequently remove it from measurements.