[Paper Review] Dispersion-controlled Temporal Shaping of Picosecond Pulses via Non-colinear Sum Frequency Generation

Randy Lemons, Nicole Neveu+4 more|arXiv (Cornell University)|Dec 3, 2020

Gyrotron and Vacuum Electronics Research4 citations

TL;DR

This paper presents a dispersion-controlled, non-collinear sum frequency generation technique that directly encodes intensity-envelope shaping into the nonlinear upconversion process, enabling precise temporal shaping of picosecond pulses. Applied to the LCLS-II photoinjector, this method reduces transverse electron beam emittance by at least 25% compared to conventional pulse shaping, significantly enhancing electron beam brightness.

ABSTRACT

Temporally shaping upconverted laser pulses to control and improve the electron beam characteristics in photocathode emission is a long-sought-after challenge. Conventionally in the ultraviolet range, tailoring of these pulses can significantly enhance the brightness of ultrafast electron sources and accelerator-based light sources. We present a novel and efficient upconversion technique where the intensity-envelope shaping is encoded in the nonlinear conversion stage, thereby circumventing commonly adopted trade-offs in photoinjector systems worldwide. To highlight its impact, we also present a real-world case-study of the LCLS-II photoinjector where the transverse electron emittance is improved by at least 25% relative to conventional pulse-shape configurations.

Motivation & Objective

• To overcome the trade-offs in photoinjector systems that limit electron beam brightness due to conventional pulse-shaping methods.
• To develop an efficient upconversion technique that integrates intensity-envelope shaping directly into the nonlinear conversion process.
• To enable dispersion-controlled temporal shaping of ultrashort laser pulses for improved performance in photocathode electron sources.
• To demonstrate the practical impact of this method on real-world accelerator systems, such as the LCLS-II photoinjector.
• To achieve enhanced electron beam emittance control without compromising pulse duration or peak power.

Proposed method

• Utilizes non-collinear sum frequency generation (SFG) to convert near-infrared picosecond pulses into the ultraviolet range while encoding temporal intensity shaping in the nonlinear interaction.
• Employs dispersion control in the SFG setup to tailor the temporal profile of the upconverted pulse, allowing precise shaping of the intensity envelope.
• Integrates the shaping function directly into the nonlinear conversion process, eliminating the need for separate, lossy pulse-shaping elements.
• Leverages phase-matching conditions in non-collinear geometry to enable efficient and flexible spectral and temporal control of the output pulse.
• Applies the shaped UV pulse to a photocathode to generate electron beams with tailored temporal and spatial characteristics.
• Uses the LCLS-II photoinjector as a testbed to validate performance improvements in electron beam emittance.

Experimental results

Research questions

• RQ1 Can intensity-envelope shaping be directly encoded in the nonlinear upconversion process to avoid trade-offs in photoinjector systems?
• RQ2 How does dispersion control in non-collinear sum frequency generation affect the temporal profile of upconverted pulses?
• RQ3 To what extent can this method reduce transverse electron beam emittance in a real-world photoinjector system?
• RQ4 What is the impact of this shaping technique on the brightness of ultrafast electron sources compared to conventional pulse-shaping methods?
• RQ5 Can this approach be effectively scaled or adapted to other accelerator-based light sources?

Key findings

• The proposed upconversion technique successfully encodes intensity-envelope shaping directly within the nonlinear conversion process, eliminating the need for external pulse-shaping components.
• The method enables precise, dispersion-controlled temporal shaping of picosecond pulses in the ultraviolet range, critical for high-brightness electron sources.
• In the LCLS-II photoinjector case study, the transverse electron beam emittance was reduced by at least 25% compared to conventional pulse-shape configurations.
• The technique improves electron beam brightness by enabling better control over photocathode emission dynamics without degrading pulse quality.
• The approach demonstrates a practical solution to long-standing trade-offs in photoinjector systems, offering a path to enhanced performance in ultrafast electron and light sources.
• The results confirm that direct shaping in the nonlinear conversion stage is both feasible and highly effective for next-generation accelerator applications.