Laser interaction with a nanobrush target plasma is investigated at the SILEX-I laser facility [X. F. Wei et al., J. Phys. Conf. Ser. 112, 032010 (2008)] with a laser of intensity 7.9×1018 W/cm2. Highly collimated fast electron beams with yields of more than three times higher than that from the planar target can be produced. Two-dimensional particle-in-cell simulation confirms that a layered surface structure can increase the efficiency of laser energy absorption, and the resulting fast electrons are tightly collimated and guided by the plasma layers to a cross section of about the laser spot size.
A simple multiwavelength Tm-doped fiber laser at the 2 μm band based on multimode interference (MMI) is proposed and experimentally demonstrated. In this scheme, a 4 m Tm-doped single-mode fiber is pumped by a 1568 nm laser, and a single-mode-multimode-single-mode (SMS) fiber structure is used as an MMI filter in which the multimode fiber is used to tune the laser. Laser operation of up to three wavelengths is obtained based on the MMI filter. The wavelengths can be tuned by adjusting the polarization controller and rotating the multimode fiber in the SMS structure, and the tuning region is about 24 nm, i.e., 1892-1916 nm. The side-mode suppression ratio of the laser is about 54 dB. The 3 dB linewidth is less than 0.04 nm. Peak fluctuation at each wavelength is analyzed, and the results show that the power fluctuation is less than 3 dB around the average power.
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