Development of Carrier-Envelope-Phase-Stabilized, mJ-Class Laser Sources Generating Intense, Few-Cycle Laser Pulses

Over a decade ago the frontiers of ultrashort physics and nonlinear optics have reached the attosecond timescale ($1 as = 10 ^ {-18} s$) . Currently, in order to generate isolated attosecond pulses, an intense femtosecond pulse is focused in a jet of a noble gas. Given the sufficient intensity, this leads to high harmonic generation (HHG), which can be filtered (gated) to create a single isolated attosecond pulse. The laser source for the driver pulses has to fulfill two requirements: the pulses need to be limited to the duration of only few optical cycles (<6 fs in case of the central wavelength of 800 nm) and the electric waveform needs to be stable. The latter in practice translates to the stability of the phase between the carrier wave and the pulse envelope. This quantity is known as the carrier-envelope phase (CEP). As the field of attosecond physics expands, more accent is put on the reliability and robustness of the few-cycle, CEP-stable laser sources. This work addresses two distinct challenges in this area. Currently, in order to generate mJ-level, few-cycle pulses the following approach is usually undertaken. First, nJ-level femtosecond pulses are generated in a laser oscillator. The generated oscillator pulses are stretched to tens or hundreds of picoseconds and injected into a laser amplifier. The pulses are then amplified to the mJ-level. This amplification method is known under the name of chirped pulse amplification. When the gain medium in the amplifier is titaniumsapphire (Ti:Sa) crystal, the pulse duration after the re-compression is on the order of 30 fs. As of this moment, it is not possible to achieve direct few-cycle output due to the effect known as the gain narrowing. This phenomenon stems from the Gaussian/Lorentzian profile of the gain curve, leading to stronger amplification of the spectral components near the gain maximum. Therefore, during the amplification process the spectrum of the pulses becomes narrower and the duration of the compressed output pulses increases. The gain narrowing presents the reason why the amplifier output duration is limited to the 30-fs range. Hence, for achieving mJ-level, few-cycle pulses, these 30-fs amplifier pulses must be spectrally broadened using a nonlinear scheme and re-compressed afterwards, achieving the few-cycle regime. This leads to more complicated, less stable setups and ultimately sets a limit on the achievable energy of the few-cycle pulses. There is also a trend in attosecond physics to perform experiments with more energetic XUV photons. This can be done by utilizing driver sources in the longer wavelength region. The reason for this is the scaling of the high harmonic cut-off frequency (which gives the most energetic photons) with l2 of the driver laser wavelength. However, the reverse scaling of $λ ^{-5.5}$ of the HHG efficiency makes the wavelengths in the far-infrared region less useful. In practice, this trade-off leads to the necessity of driver sources in the mid-infrared region (3-5 μm). Since there is currently no laser medium with a sufficiently broadband (for supporting few-cycle duration) emission curve in this wavelength region, the efforts have been concentrated on the development of parametric sources. When it comes to parametric sources in the mid-infrared, multitude of pump/seed sources and nonlinear crystals present viable options. As it stands, there is no universally accepted or “standard” scheme for generating few-cycle pulses in this wavelength region - various setups have their own up- and downsides. In the scope of this work, two unique laser systems with a stable CEP are developed to tackle the described challenges. The first laser system is an ultrabroadband, CEP-stable Ti:Sa amplifier. The compensation of the gain narrowing using custom spectral filters leads to a compact and robust amplification stage with a combination of output pulse parameters that has never before been demonstrated in the scientific literature. The direct output is CEP-stable with pulse duration of sub-13 fs and energy of 3:2 mJ. This system presents a major step forward towards direct generation of few-cycle, mJ-level pulses. The second laser system is a CEP-stable, potentially few-cycle mid-infrared parametric amplifier. It is pumped/seeded by a 30-fs Ti:Sa amplifier. The presented source explores the viability of using ultrashort laser pulses as pump/seed source for the system. The undertaken approach results in compressed, CEP-stable output with 300 μJ energy per pulse at the 3:4 μm central wavelength. The spectrum of the generated pulses supports few-cycle duration. Such a result has not been demonstrated before for Ti:Sa-pumped parametric amplifiers. This presents an important step towards simpler and more robust parametric sources in this wavelength region. In this work, the connection between these two systems is also outlined. Namely, the use of the presented ultrabroadband Ti:Sa amplifier as a prospective pump/seed source for the developed mid-infrared parametric amplifier. At the end of the thesis, results of two-color HHG experiments with the mid-infrared parametric amplifier are presented.