Yüksek tekrarlama frekanslı femtosaniye Cr:LiCAF lazerlerinin geliştirilmesi ve çok yansımalı Ti:Safir lazerinin THz radyasyonu üretimindeki uygulaması

There is a great deal of interest for developing low-cost, robust, compact and efficient femtosecond lasers for time and frequency domain applications. In recent years, Cr^(3+)-doped colquiriites (Cr:LiSAF, Cr:LiCAF, Cr:LiSGaF) have emerged as promising alternatives to Ti:Sapphire lasers near 800 nm because of numerous favorable laser characteristics. These include the possibility of direct diode pumping with low cost diodes, broad emission bands to generate fs pulses and high quantum efficiency near room temperature. The first part of this thesis work focuses on the design and experimental demonstration of a directly diode pumped, low cost, and highly efficient 800-nm Cr:LiCAF laser which can be operated above 100 MHz with the goal of developing high repetition rate oscillators for frequency comb applications. In the experiments, a four mirror x-cavity laser containing a 7% doped Cr:LiCAF crystal was endpumped with a recently developed high brightness, 1-W tapered diode at 675 nm. By using 915 mW of pump power, the Cr:LiCAF laser produced 340 fs pulses around 800 nm with an output power of 51 mW, at a repetition rate of 120 MHz. A semiconductor Bragg reflector (SBR) was added into the resonator to initiate the mode- locked operation of the laser. We expect that, with the higher pump powers available from the tapered diode, it should be possible to reach GHz level repetition rates with this resonator for frequency comb applications. The second part of the thesis work utilizes a home-built multi-pass cavity femtosecond Ti:Sapphire laser, generating 98 fs pulses with a repetition rate of 5.53 MHz at 776 nm, to obtain THz radiation from a photoconductive antenna. The output of the Ti:Sapphire laser with an average power of 60-70 mW power was focused on a low-temperature grown GaAs (Lt-GaAs) structured photoconductive antenna which generated THz waves with a signal strength of 5 mV detected with a second photoconductive antenna. The generated THz waves were in the frequency range of 0.1-0.7 THz. With improved antenna and detection design, we expect to further improve the bandwidth and efficiency of THz generation.