Valentina Shumakova

This article provides an overview of laser-based absorption spectroscopy applications and discusses the parameter space and requirements of laser systems for each of these applications, with a special emphasis on frequency comb systems. We walk the reader through the basics of laser absorption spectroscopy, review common line-broadening mechanisms as fundamental challenges to precision spectroscopy, look into established solutions, introduce frequency-comb-based absorption spectroscopy, and suggest a novel approach to broadband precision spectroscopy in the mid-infrared spectral region based on a combination of broadband high-power ultra-stable optical frequency combs, crystalline supermirror technology, and an instrumental line-shape-free measurement technique. We conclude after an introduction of noise sources and their implications for precision measurements with an in-depth discussion and overview of the current state-of-the-art laser and optical parametric frequency conversion technologies.

Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser, and therefore high average power, pulse duration of a few tens of fs, and maximal available spectral bandwidth. Contrarily, the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations. Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification (CPA) to the requirements of different nonlinear frequency converters while preserving the low-phase-noise (PN) properties of the system. To achieve spectral tunability, we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system. The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz. While gaining control over the spectral properties, we preserve the relative-intensity-noise and PN properties of the system. The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation (full width at half maximum of ∼ 11    nm , compressed pulse duration of 230 fs) or a spectrum ideal for highly nonlinear processes such as high-harmonic generation ( - 10   dB level of > 50    nm , transform-limited pulse duration of ∼ 65    fs ).

We report on 100-W 132 MHz Yb:fiber amplifier seeded by a low noise oscillator. We tune the laser spectrum to match it to different applications while keeping noise properties and power performance of the system.

Intense laser fields focused into ambient air can be used to generate high-bandwidth current densities in the form of plasma channels and filaments. Excitation with bichromatic fields enables us to adjust the amplitude and sign of these currents using the relative phase between the two light pulses. Two-color filamentation in gas targets provides a route to scaling the energy of terahertz pulses to microjoule levels by driving the plasma channel with a high-energy laser source. However, the structure of plasma channels is highly susceptible to drifts in both the relative phase and other laser parameters, making control over the waveform of the radiated terahertz fields delicate. We establish a clear link between the phase dependence of plasma currents and terahertz radiation by comparing in situ detection of current densities and far-field detection of terahertz electric fields. We show that the current measurement can be used as a feedback parameter for stabilizing the terahertz waveform. This approach provides a route to energetic terahertz pulses with exceptional waveform stability.

Since its first demonstration, laser induced aerosol formation (LIAF) has been studied in various environmental conditions and laser parameters. LIAF driven by UV and near-IR lasers mainly relies on the nitrogen photo-oxidative chemistry, leading to the production of hygroscopic H N O 3 , which stabilizes the growth of aerosol nanoparticles. Mid-IR lasers were expected to be drastically less effective for LIAF, due to their much lower multiphoton photodissociation and ionization rates. Here, we report on the observation of surprisingly high yields of nanometric and sub-µm aerosol formation driven by mid-IR laser pulses, which cannot be explained by the H N O 3 -pathway. We hereby evidence a new mechanism of aerosol stabilization and growth, based on the resonant excitation of volatile organic compounds (VOCs) by mid-IR pulses whose spectrum is broadened during filamentation.

We demonstrate that intense free space THz fields can nonlinearly induce excitonic photoluminescence in room temperature semiconductors as well as cross-phase modulation in an electro-optic crystal.