T. Denis

Coherent Cherenkov radiation and laser oscillation in a photonic crystal

We demonstrate that photonic crystals can be used to generate powerful and highly coherent Cherenkov radiation that is excited by the injection of a beam of free electrons. Using theoretical and numerical investigations we present the startup dynamics and coherence properties of such a laser, in which gain is provided by matching the optical phase velocity in the photonic crystal to the velocity of the electron beam. The operating frequency can be varied by changing the electron beam energy and scaled to different ranges by varying the lattice constant of the photonic crystal.

Mapping the absolute electromagnetic field strength of individual field components inside a photonic crystal

We present a method to map the absolute electromagnetic field strength inside photonic crystals. We demonstrate our method by applying it to map the electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to create a resonator and a subwavelength spherical scatterer is scanned inside the resonator. The resonant Bloch frequencies shift depending on the electric field at the scatterer position. By measuring the frequency shift in the reflection and transmission spectrum versus the scatterer position we determine the field strength. Excellent agreement is found between measurements and calculations without any adjustable parameters and a possible realization is suggested for measurements at optical frequencies.

Single-mode power scaling in a multi-beam photonic free-electron laser

Multi-beam slow-wave devices, such as photonic free-electron lasers (pFEL), are promising for power up-scaling of THz sources. However, multi-beam concepts usually require wide and hence overmoded slow-wave structures. This could lead to undesired multimode output. Here, we present single-mode power up-scaling of a pFEL when increasing the electron beam number.

Study of beam focusing techniques for a power- and frequency scalable photonic free-electron laser

In this paper, we study the feasibility and suitability of two beam focusing techniques, i.e., Brillouin-and immersed flow, to be used in a novel device which can be up-scaled in power via increasing the number of beams, and in frequency via reducing the spatial period of the photonic crystal.

A mirrorless photonic free-electron laser oscillator

Photonic crystals have been used to provide fundamental control over the interaction between light and matter, including stimulated emission. For example, in Bloch-mode lasers, the photonic crystal provides field enhancement through reduced group velocity and offers larger mode volumes through distributed feedback [1]. In a photonic free-electron laser (pFEL) [2], where electrons stream through a photonic crystal (see Fig.1), gain and coherent output is provided by free electrons through the emission of coherent Cherenkov radiation. The property of this radiation mechanism is that the optical gain can be scaled over a large range of the electromagnetic spectrum via selecting an appropriate spatial period of the photonic crystal, and be tuned continuously via the electron velocity. Furthermore, due to the periodic dispersion of the Bloch modes, the pFEL can be operated in the so-called backward wave regime where the group velocity is directed opposite to the phase velocity. In this regime, light generated downstream in the photonic crystal travels upstream, where it bunches the electron beam [2]. The increased bunching subsequently increases the downstream emission. Consequently, the backward wave interaction provides a feedback mechanism and creates an oscillator without the need for external mirrors. This mirrorless oscillator can provide continuously tunable, narrow bandwidth light, for use in, e.g., spectroscopic applications.

Power scalability of a low-current multi-beam photonic free-electron laser

A photonic Free-Electron Laser is a novel device concept that uses multiple electron beams and a photonic crystal to enable both frequency- and power-scaling. Particle-in-cell calculations show that the three-beam provides more than 3× the power of the single-beam device, 290 vs 35 W.

A photonic free-electron laser

Sending electrons through photonic crystals (PhC) is of high interest for generating widely tunable, coherent light. We present the novel concept of a tunable laser based on Cerenkov radiation from electrons in a PhC.

Method to map individual electromagnetic field components inside a photonic crystal

We present a method to map the absolute electromagnetic field strength inside photonic crystals. We apply the method to map the dominant electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to select Bloch standing waves and a subwavelength spherical scatterer is scanned inside the resulting resonator. The resonant Bloch frequencies shift depending on the electric field at the position of the scatterer. To map the electric field component Ez we measure the frequency shift in the reflection and transmission spectrum of the slab versus the scatterer position. Very good agreement is found between measurements and calculations without any adjustable parameters.

P3-30: Slow - wave structure for a photonic free - electron laser

Photonic free-electron lasers (pFEL) are a promising concept for compact, Watt-level THz sources. We present here the design and characterization of its slow-wave structure at 8–10 GHz. This research is the first step to develop pFELs at THz frequencies.