Laser beam profile analysis of a hole coupled free-electron laser

We present measurements and numerical simulations of the laser beam transverse profile of the CLIO infrared free-electron laser (FEL). This FEL uses a hole coupling extraction system, which introduces important perturbation on the intracavity optical mode. We show that this intracavity mode tends to avoid the extraction hole and that the output power optimization leads to an off-axis laser alignment inside the FEL cavity.

Figure 1

Schematic layout of the CLIO free-electron laser optical cavity.

Figure 2

Experimental setup of the laser profile measurement.

Figure 3

Measurement of laser mode transverse profiles, in the experimental room, at $\lambda =6.7\mu \mathrm{m}$ (a), and $\lambda =17\mu \mathrm{m}$ (b).

Figure 4

Numerical simulation of output laser power versus a tilt of the output mirror.

Figure 5

Numerical simulation of the laser mode transverse profile, calculated in the experimental room, on the detector plane, at $\lambda =6.7\mu \mathrm{m}$ (a), and $\lambda =17\mu \mathrm{m}$ (b).

Figure 6

Numerical simulation of the laser mode profile on the downstream mirror, (a) at $\lambda =6.7\mu \mathrm{m}$, and (b) at $\lambda =17\mu \mathrm{m}$.

Figure 7

Numerical simulation of the laser mode profile, for $\lambda =6.7\mu \mathrm{m}$, at normal incidence at the downstream mirror, (a) on cavity output mirror, and (b) in experimental room.

Figure 8

Numerical simulation of the laser mode profile with a tilt $\theta =0.4\mathrm{mrad}$ at 45° on the downstream mirror, (a) on cavity output mirror, and (b) in the experimental room.