Very high resolution optical transition radiation imaging system: Comparison between simulation and experiment

Optical transition radiation (OTR) has become a commonly used method for 2D beam imaging measurements. In the Accelerator Test Facility 2 (ATF2) at KEK, beam sizes smaller than the OTR point spread function have been measured. Simulations of the OTR imaging system have been performed using the ZEMAX software to study the effects of optical errors such as aberrations, diffraction, and misalignments of optical components. This paper presents a comparison of simulations of the OTR point spread function with experimental data obtained at ATF2. It shows how the quantification and control of optical errors impacts on optimizing the resolution of the system. We also show that the OTR point spread function needs to be predicted accurately to optimize any optical system and to predict the error made on measurement.

Figure 1

Simulation of the 2D distribution of vertically polarized OTR irradiance generated at the target by a single electron.

Figure 2

The far-field OTR angular distribution calculated by ZEMAX for different OTR field radius ($\lambda =550\mathrm{nm}$; $\gamma =50$).

Figure 3

OTR angular distribution calculated by ZEMAX for $\lambda =550\mathrm{nm}$ and for different energies.

Figure 4

OTR PSF distribution simulated by ZEMAX for $\lambda =550\mathrm{nm}$ and for different energies.

Figure 5

OTR PSF distribution simulated by ZEMAX for $\gamma =2500$.

Figure 6

OTR PSF distribution calculated by ZEMAX for different types of lenses and for $\gamma =2500$.

Figure 7

Expected vertical beam profile obtained from the convolution of the ATF2 OTR PSF with a Gaussian beam distribution. Simulations are performed for $\lambda =550\mathrm{nm}$ and $\gamma =2500$.

Figure 8

Simulated output beam size versus input beam size. The line in red shows the ideal curve where output beam size equals the input beam size.

Figure 9

Experimental setup of the high-resolution OTR imaging system at ATF2/KEK.

Figure 10

Typical beam image (a) and corresponding horizontal (b) and vertical (c) profiles.

Figure 11

Distance between OTR PSF peaks as a function of the longitudinal position of the lens ($\gamma =2500$; $\lambda =550\mathrm{nm}$).

Figure 12

OTR PSF measured at best focus for 500, 550, and 600 nm wavelength optical filters.

Figure 13

Vertical projection of the PSF measured and simulated with the plano-convex lens (top) and the achromatic lens (bottom) at the best focus ($\gamma =2500$; $\lambda =550\mathrm{nm}$).

Figure 14

OTR PSF measured for an achromatic lens with 550 nm optical filters of 25 and 40 nm bandwidth.

Figure 15

OTR PSFs measured for different iris diameters ($\gamma =2500$; $\lambda =550\mathrm{nm}$).

Figure 16

OTR PSF size for different iris diameters and $\lambda =550\mathrm{nm}$, $\gamma =2500$.