Spatially Resolved Spectral Imaging by A THz-FEL

Using the unique characteristics of the free-electron-laser (FEL), we successfully performed high-sensitivity spectral imaging of different materials in the terahertz (THz) and far-infrared (FIR) domain. THz imaging at various wavelengths was achieved using in situ spectroscopy by means of this wavelength tunable and monochromatic source. In particular, owing to its large intensity and directionality, we could collect high-sensitivity transmission imaging of extremely low-transparency materials and three-dimensional objects in the 3–6 THz range. By accurately identifying the intrinsic absorption wavelength of organic and inorganic materials, we succeeded in the mapping of spatial distribution of individual components. This simple imaging technique using a focusing optics and a raster scan modality has made it possible to set up and carry out fast spectral imaging experiments on different materials in this radiation facility

High power light source for future EUV lithography based on ERL-FEL

The continuous development to increase the intensity of the EUV light source for future EUV lithography is important to realize the high through put fine patterning. The ERL-FEL, which is an accelerator based light source, would be one of the candidates for this one. This paper clarifies the design concept of the ERL-FEL for EUV light source for future lithography, the delivery systems of the FEL light to multi-scanners and also future development items of the accelerator technologies and a possibility of the beyond EUV

Extremely High-Intensity Operation of a THz Free-Electron Laser using an Electron Beam with a Higher Bunch Charge

A higher intensity THz beam is generated with a free-electron laser (FEL) based on the L-band (1.3 GHz) electron linac at Osaka University by increasing the electron bunch charge four times higher from 1 nC in the conventional mode (the 108 MHz mode) to 4 nC in the new mode (the 27 MHz mode). This is realized by expanding the electron bunch intervals four times longer with the grid pulser of the electron gun generating a series of 5 ns pulses at a repetition frequency of 27 MHz (the 48th sub-harmonic of 1.3 GHz), whereas the beam loading of the linac remains unchanged. The energy of an FEL macropulse comprised of many micropulses is measured in the 27 MHz mode to be approximately 28.5 mJ at a maximum of around 65 μm or 4.6 THz compared with the maximum macropulse energy of 13 mJ in the 108 MHz mode. The maximum micropulse energy in the 27 MHz mode is calculated to be approximately 260 μJ using 110 micropulses, which is estimated by a macropulse duration of 4 μs and micropulse intervals of 36.9 ns. The micropulse energy is nearly 10 times higher than the micropulse energies in the conventional mode and in other FELs in the same wavelength or frequency region

Rigorous evaluation of the edge-focusing wiggler based on the magnetic field measurement

The edge-focusing (EF) wiggler, which produces the strong field gradient for transverse focusing incorporated with the normal wiggler field, has been fabricated to evaluate its performance rigorously with the magnetic field measurement. It is a five-period planar wiggler with an edge angle of 2° and a period length of 60 mm. The magnetic field in the wiggler is measured using Hall probes at four different wiggler gaps. It is experimentally confirmed that a high field gradient of 1.0  T/m is realized, as designed, along the beam axis in the EF wiggler. The magnetic field gradient of the EF wiggler is derived as a function of the magnetic gap. The field gradient decreases with increasing magnet gap more slowly than the peak magnetic field does for the present experimental model. An analytic formula for the field gradient of the EF wiggler is derived and it is shown that the slope of the field gradient with the magnet gap can be changed by varying the magnet width of the EF wiggler