Polarization encoded (PE) Ti:sapphire amplifier can easily pre-shape the spectrum of amplified pulses. This property can be used to compensate for the spectral red-shifting and gain narrowing that are typically observed in Ti:Sapphire lasers. We demonstrate experimentally that active pre-shaping of the pulse spectrum in a PE amplifier combined with saturated amplification in the following conventional amplifier can conserve and even broaden the overall amplification bandwidth.
A combined amplifier that includes PE- amplification (during the first passes) and a conventional one in the following saturation phase is also proposed and studied by computer modelling. This allows to achieve both the broad bandwidth and high efficiency in a single amplifier. A 5 passes combined PE amplifier was simulated. The seed was firstly amplified by 3 passes with the PE amplification scheme, then the seed was decoded and directed back to the crystal for 2 additional passes of a saturated conventional amplification. Because the seed was already decoded before the last saturation passes in the amplifier, the energy extraction efficiency reached 44% which is similar to that of a conventional Ti:sapphire amplifier. The amplified bandwidth of 125 nm was obtained with a Gaussian seed spectrum of 100nm.
We show experimentally that the decoding efficiency of PE amplifier can be optimized by changing the thickness of the decoding quartz. At gain of ~30, the decoding efficiency of ~75% was achieved with the thickness of the decoding quartz of 35.1mm (thickness of the encoding quartz was 17.4mm), while the decoding efficiency of 80% was reached at gain of ~10. It shows that smaller gain guaranties better efficiency and also a smoother spectral profile.
The compressibility of the PE amplified pulses close to the transform limit is verified experimentally.
Huabao Cao, Mikhail P. Kalashnikov, Károly Osvay, Nikita Khodakovskiy, Roland Sándor Nagymihály, and Vladimir V. Chvykov, "Active spectral pre-shaping with polarization encoded amplifiers (Conference Presentation)," Proc. SPIE 10238, High-Power, High-Energy, and High-Intensity Laser Technology III, 1023809 (Presented at SPIE Optics + Optoelectronics: April 26, 2017; Published: 9 June 2017); https://doi.org/10.1117/12.2264702.5463398607001.
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