Electron-Beam Characterization Sensors Based on Lithium Niobate Modulators

Non-destructive and least-invasive characterization techniques to understand the dynamics and evolution of the accelerated beam transverse and longitudinal phase space are of great interest due to their indispensable role as drivers of X-ray Free Electron Laser (XFEL) light sources. Electro-optical sampling of the electron beam bunch is ideal for precise and non-destructive measurement of the temporal profile of extremely short electron bunches. The temporal and spatial properties of accelerated particles can be determined using a probe light that is influenced by an electro-optical crystal placed near the beam path. ZnTe and GaP have been used in the past to modulate femtosecond lasers in THz frequencies since they allow phase matching between THz signal and optical signal. These two electro-optical materials have low electro-optic coefficient as well as low operation bandwidth limited to 2-3 THz. As opposed to these crystals, lithium niobate has a very large electro-optic coefficient. Lithium niobate, however, has not been used in the past for sampling of the electric field of electron bunch. The dielectric constant of lithium niobate is much higher at RF and THz frequencies compared to optical wavelengths. However, by using thin film lithium niobate it is possible to phase match the THz signal and optical signal and achieve terahertz modulation. We propose to use thin film lithium niobate for THz sampling of electron bunch field. Since the device have a very high sensitivity for e-field measurement, the length of device can be 100 micron or even shorter at accelerator applications and still achieve higher signal to noise ratio compared to ZnTe and GaP. 10 THz bandwidths can be readily achieved using lithium niobate thin film devices with 100 microns in length. Our proposed scheme allows extremely compact and low-cost sensors to be made for electron bunch electro-optical sampling with several order of magnitude higher sensitivity compared to state of the art techniques. The proposed approach also enables higher bandwidth to be achieved for electron bunch sampling. In phase I we plan to design and build a proof of concept chip and measure its modulation performance at THz frequencies. We will characterize the frequency bandwidths of the LiNO3 modulator by analyzing the optical sidebands resulting from the nonlinear optical interaction between THz waves and optical waves in the modulator. A variety of applications such as antenna field characterization or plasma processing equipment need e- field sensors where the electric field of an RF signal need to be sampled. Electro-optic sampling methods allow electric field sampling of RF sources to be sampled without perturbation. The technology that will be developed using this SBIR funding is directly applicable to these applications. The technology that Partow will develop based on this proposal can be also used in many different applications in communication, electronics and sensor markets. Many applications are looking for low cost, compact and robust photonic integrated circuits to enable a variety of systems. Among these applications are telecom and datacom where a compact, high-speed and low power optical signal modulator is needed. Other application of our technology is in navigation sensors such as optical gyroscopes for space and avionic applications. Partow Technologies’ modulators offer reduced-size, low-power and low-weight solutions with significantly improved performances for these applications. The technology that will be developed using this SBIR funding can be used in ultra-fast photonic assisted analog to digital convertors. There is a need for higher speed optical analog to digital convertors where high-speed sampling of electronic signals at higher frequency range is needed. The photonic technology that will be developed using this SBIR funding can be directly used to make very high-speed analog to digital convertor that are needed in many modern electronic applications.