10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources

Abstract

Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today’s ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses. So far, most of precision laser-RF synchronization has been achieved by using specially designed low-noise Er-fibre lasers at telecommunication wavelength. Here we show a modular method that achieves long-term (>1 day) stable 10-fs-level synchronization between a commercial 79.33-MHz Ti:sapphire laser oscillator and an S-band (2.856-GHz) RF oscillator. This is an important first step toward a photocathode laser-based femtosecond RF timing and synchronization system that is suitable for various small- to mid-scale ultrafast X-ray and electron sources.

Ultra-precise timing and synchronization for large-scale scientific instruments

“…On the other hand, since mode-locked lasers can provide an ultrashort pulse train with ultralow timing jitter, such an "optically assisted" phase detection can provide much higher resolution for microwave phase discrimination. In the past decades, several kinds of optical-microwave phase detectors have been demonstrated [44][45][46][47][48][49][50][51][52]. Figure 5 shows the architecture of a free-space-coupled balanced optical-microwave phase detector (BOMPD), which was first proposed in Refs.…”

Femtosecond phase control in high-field terahertz-driven ultrafast electron sources

“…Despite tremendous advances over decades of development, conventional RF-powered devices remain costly, require major infrastructure, and consume significant power, limiting the availability of these technologies to an even broader scientific community [7]. In particular for ultrafast science applications, difficulties in synchronization [8] and low acceleration gradients [9] represent serious challenges for reaching desired spatial and temporal resolutions. Strong motivation thus exists for exploring alternative "compact" technologies offering smaller sizes and costs and the potential to push the resolution frontiers.…”

fs-level laser–RF synchronization with a fiber-loop optical-microwave phase detector

“…It cannot meet the demands of accelerators nowadays. To solve the problem, a variety of laser-RF synchronization systems based on optical phase detectors have been developed with fs-level residual timing instabilities, which can be characterized by jitter and drift [8][9][10][11][12][13][14][15] . Most of these demonstrations were based on low-noise mode-locked Er-fiber lasers [8][9][10][11][12][13]15] .…”

“…Therefore, high-precision synchronization of the RF signal to the mode-locked solid-state laser is highly desirable. In early 2017, 10-fs-level synchronization was achieved between a fs Ti:sapphire laser and an RF signal [14] . However, fs-level synchronization between a picosecond laser and RF signal, which is very important for a superconducting RF accelerator, has not yet been reported.…”

“…The AM-to-PM conversion noise is determined by the laser relative intensity noise (RIN) and the phase bias unit. In order to suppress the AM-to-PM conversion noise, a RIN controller [14] can be employed to improve the power stability of the laser. Replacing the free-space unit with fiber components can also be helpful, which contributes to improving the stability of the Sagnac loop [15].…”