Nonlinear confocal positioner for micron-scale target alignment.

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.

High accuracy astigmatic-focusing system for laser targets.

An accurate location of the focal position with respect to a solid target is a key task for different applications, for instance, in laser driven plasma acceleration for x-ray generation where minimum required intensities are above 1014W/cm2. For such practical applications, new approaches for focus location and target delivery techniques are needed to achieve the required intensity, repeatability, and stability. There are different techniques to accomplish the focusing and target positioning task such as interferometry-, microscopy-, astigmatism-, and nonlinear-optics-based techniques, with their respective advantages and limitations. We present improvements of a focusing technique based on an astigmatic method with potential applications where maximum intensity at the target position is necessary. The presented technique demonstrates high accuracy up to 5 µm, below the Rayleigh range, and also its capability to work in rough surfaces targets and tilt tolerance of the target, with respect to the normal of the target surface.