In this work, we present an experimental method to characterize variable optical retarders, which can have linear or non-linear behavior of the retardance variation. A theoretical analysis of such is presented using a combination of Stokes vectors and Mueller matrixes for three different optical retarders. A straightforward method for phase unwrapping, or reconstructing the original phase from the measured retardance, is proposed that yields high-accuracy results. This work can be used in an undergraduate optics lab to help students understand the concepts of retardance and its control and also how variable retardance devices work.

In the present work, we applied an amplitude-spatial light modulator to shape the spectral amplitude of femtosecond pulses in a single step, without an iterative algorithm, by using an inversion method defined as the generalized retardance function. Additionally, we also present a single step method to shape the intensity profile defined as the influence matrix. Numerical and experimental results are presented for both methods.

This paper presents a novel target positioner system that exhibits high sensitivity and accuracy. Specifically, the system is capable of precisely locating rough target surfaces within a micron-scale in the focal plane. The high sensitivity comes from the nonlinear detection scheme which uses the two-photon-absorption process in a Si-photodiode and a CMOS sensor at 1550 [nm]. The setup employs a confocal configuration that is easy to align and does not require a conjugated focal plane selective aperture (pinhole), thus demonstrating its feasibility and tilt tolerance of the target. Moreover, the system offers high accuracy up to 5 [μm], which corresponds to the step size of the focus scanning. The presented positioner system has potential applications in microfabrication with lasers and laser-driven plasma accelerators even at high repetition rates, limited by the detection bandwidth of the photodiode. Additionally, the principle can be extended to cameras if spatial information is needed and the system design can be extended to other spectral ranges with minimal changes.

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