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In this paper, design and construction of a tunable pulsed Ti:sapphire laser and numerical solution of the corresponding rate equations are reported. Rate equations for a four-level system are written and their numerical solution is examined. Furthermore, an optical setup is introduced. In this setup, a Ti:sapphire crystal is longitudinally pumped by the second harmonics of a Q-Switched Nd:YAG laser, and a prism is used as a wavelengthselective element as well. This setup is established for two 10 and 50 % transmission output couplers. In case of using the 10 % coupler, the output energy of the laser, for the pump energy of 36 mJ, is pulses with 3.5 mJ energy and for the 50 % coupler, with 50 mJ of pump energy, pulses with 10 mJ energy are generated. A wavelength tuning range of more than 160 nm is possible. The repetition rate of this laser is 10 Hz and the temporal duration of the pulses is about 30 ns.

In this work, the finite difference time domain (FDTD) method is used to optimize the multi-pixel sampling approach, in order to achieve ultra-high spatial resolution (∼ λ/110) in the near-field region. The optimization is performed based on the optical pump pulse wavelength, the thickness of the silicon modulator, and the size of the aperture in the projected pattern. To the best of our knowledge, this is the first time that the FDTD method has been used to improve near-field resolution. In addition, we consider the effect of pump wavelength on near field imaging resolution for the first time.

The performance of the magnesium fluoride/chromium/gold in-line fiber optic polarizer on the thickness of magnesium fluoride buffer layer and chromium metal thin film was theoretically investigated. To prove the theoretical study, the magnesium fluoride/chromium/gold polarizer was made based on the simulation results. The obtained polarizer showed an extinction ratio of about 40 dB which is in a good agreement with the theoretical result at the corresponding thicknesses. Both theoretical and experimental results showed that by covering the side polished single mode fiber with the optimum layer thicknesses, a novel and an efficient fiber polarizer with the high extinction ratio could be obtained. This is the first time that this type of polarizer has been made.

Since many applications of terahertz spectroscopy depend on spectral bandwidth, the generation of ultra-broadband terahertz radiation is one of the most important challenges faced by terahertz scientists. Spintronic terahertz emitters (STEs) are promising sources to produce very compact terahertz pulses and broadband spectra. Here we optimized the iron/gold heterostructure based on the metal layer thicknesses for the first time. The optimization was performed experimentally based on the obtained theoretical results. The optimized thicknesses were obtained as 2 and 5 nm for Fe and Au layers, respectively. The experimental results were in very good agreement with corresponding theoretical results. The optimized STE generates terahertz bandwidth up to 4 THz which is limited by the frequency response of the used detector. The dynamic range is well above 60 dB with the maximum around 0.5 THz. The results show that the presented STE is capable of producing large amplitude terahertz pulses and broadband spectral range. Based on our knowledge, this is the first time that the Fe/Au spintronic terahertz emitter has been optimized.