The lasers and conventional optics used in charged-particle beam x-ray free electron laser photo-injectors are designed using fundamentally the same techniques for decades. We present a novel method for the generation and conditioning of the UV laser used for electron generation via photoemission that can enhance electron beam and X-ray performance. Additionally, we discuss laser-based spatio-temporal shaping and conditioning of electron beam phase space in order to selectively promote lasing operational modes.
Ultralow phase-noise mode-locked lasers are crucial for real-world applications. We present two accomplishments: (1) short-term FF CEP stabilization of a SESAM mode-locked Er:Yb:glass laser at 1.55 um with timing jitter below 3 as (1-3 MHz) and (2) a hybrid solution adding a FB technique addressing slowly varying sources of interference to the FF system that demonstrates 75 hours of stabilization with a minimally detrimental effect amounting to a timing jitter of 11 as.
The structuring of laser light with non-diffracting vector distributions, optical vortices, or high angular momentum are being increasing exploited. We present a system for the synthesis of these arbitrary intensity and phase profiles through a number of carrier-envelope-phase stabilized coherent frequency and spatial combs. Adjusting the differences between adjacent combs allows synthesis of a combined field which can be structured, directed, and improved in the presence of propagation noise. Additionally, we present a method for the optimization of such systems in free space with a Fourier optics based genetic algorithm that converges to <π/10 accuracy of the initial parameters.
In simultaneous spatial and temporal focusing (SSTF) a wide bandwidth pulse with transverse spatial chirp is focused, resulting in a pulse that is temporally compressed only near the focal plane. The pulse also has a pulse front tilt angle that depends on the amount of initial transverse chirp. In this work, we explore computationally and experimentally the properties of SSTF vortex and vector beams. To analyze the beam propagation, we build on the concept that a spatially chirped beam is a superposition of Gaussian beams with a position or angle that depends on frequency. We extend this to superpositions of Hermite-Gauss high-order modes to describe the singular beams. At focus, the beams of the ultrashort pulses are tilted versions of the familiar doughnut beams. Away from focus, however, where the spectral components do not fully overlap, we find that vortex and vector beams result in strikingly different mapping of the singularity mapping in the spatio-temporal domain. The use of higher-order modes increases the focal spot size without reducing the already short SSTF depth of focus. Experimentally, we use spiral phase plates to produce vortex beams and a linear to radial polarization converter for the vector beams. The vector beam is not distorted by the polarization-insensitive transmission gratings. The spatial chirp compressor is improved over our previous work to vary the chirp positive and negative. The sensitivity of the singular beam focus to grating misalignment can actually be used to optimize the compressor alignment.
In simultaneous spatial and temporal focusing (SSTF) a wide bandwidth pulse with transverse spatial chirp is focused, resulting in a pulse that is temporally compressed only near the focal plane. The pulse also has a pulse front tilt angle that depends on the amount of initial transverse chirp. Using an improved design of an asymmetric pulse compressor, we can easily vary the amount of output spatial chirp and thus the pulse front tilt at the focus. We direct this beam into a vacuum chamber and focus it onto an argon gas jet to achieve high harmonic generation (HHG). Since the harmonics are created with a tilted pulse, they emerge from the focus with an amount of angular chirp based on the input spatial chirp and harmonic number. We angularly disperse the harmonics in the direction perpendicular to the spatial chirp with a curved reflective grating, which focuses in the spectral direction onto an x-ray CCD camera. We observe that each of the harmonics possesses angular spatial chirp. To our knowledge, this is the first experimental verification of our earlier published theory of spatially chirped high harmonics. These harmonics are in a sense the Fourier complement to harmonics produced with the Lighthouse Effect. In that case, the attosecond pulse train is angularly dispersed while here each harmonic has angular spectral dispersion. This technique could be used for hyperspectral XUV spectroscopy and, when the beam is refocused, would allow for temporal focusing of the attosecond pulse train.