Orateur
Description
Pump–probe experiments with focused laser pulses are nowadays widely used in non-linear physics and time-resolved science. In such experiments, the signal depends on the quality of the beams spatial overlap. Here, we propose a simple method to characterize the beams around their focus in a single shot basis. With two beams, the device performs a snapshot of their (x-y-z)-focus that quantify the overlap quality.
The usual solution to characterize a beam around its focus consists in scanning the position of a camera around its focal point. The scanning system is usually a problem in terms of alignment, space requirement, and prevent single-shot acquisition. Here, we propose to replace the scanning system by two highly reflective ($\sim$90 %) mirrors inserted between the lens and the camera as shown in Fig. 1(a). The two mirrors are set parallel with the reflective surfaces facing each other (Fabry–Perot (FP)), but with the laser beam slightly off-axis with respect to the mirror surfaces. The off-axis FP spatially separates the transmitted beams as a function of the round-trip number in the cavity. The successive transmitted beams have experienced a free propagation length of approximately twice the distance between the mirrors (2e). This configuration allows a snapshot of the beam’s spatial profile around its focus as schematically represented in Fig. 1(b)(c). For two beams, in crossed configuration, the snapshot quantifies the beam overlap quality.
Experimental results will be shown during the conference, with the characterization of the individual beams and the quantification of the spatial overlap quality. The device requires a very low light intensity. Different solutions allow to use it in parallel with a running pump-probe experiment. This monitors the beam crossing quality in real time avoiding potential artefacts.
Figure 1 (a) schematic representation of the experimental setup: the two beams are focused with their own focal lens (L1 and L2) and are recombined with a beam splitter (BS). A beam sampler (GS) sends the beams to the off-axis-FP before reaching the camera. Schematic focusing snapshot for (b) a single beam and for (c) two beams in crossed configuration. The following sub-images correspond to the spatial profile around their focus. From left to right, the beams cumulate 2e free propagation distance, with e the separation between the FP-mirrors.
| Do you submit an abstract for a talk or a poster? | talk |
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| If your abstract isn’t selected for a plenary talk, would you like to present it as a poster? | Yes |