Understanding the temporal dynamics of light-matter interaction can transform how we identify materials and can offer novel pathways for nonlinear wavelength conversions, spectroscopy, micromachining and developing diagnostic and therapeutic approaches. The femtosecond (1 fs = 10^-15 s) temporal duration of low-noise compact fiber laser sources that are being developed in the group offer remarkable timing precision, high peak intensities and allow material studies at fast time scales, offering a glimpse into the dynamics of our universe that cannot be revealed with electronics.
In femtosecond mode-locked lasers, a broadband frequency spectrum is generated that consists of individual optical lines and that can be stabilized into an optical frequency comb, for which the Nobel Prize in Physics was awarded in 2005. Frequency combs constitute an absolute optical ruler that provide unprecedented wavelength accuracy and reproducibility and enabled revolutionary optical clock applications, frequency metrology, and high resolution spectroscopy.
While mode-locked solid-state have established themselves at the forefront of broadband and low-jitter optical sources, their bulkiness, alignment sensitivity and cost have prevented their direct integration into more portable applications. Therefore, to enable wider adoption of the technology and novel applications like next generation communication systems, medical imaging, micromachining or the calibration of astronomical spectrographs, it is our goal to develop novel femtosecond laser designs with robust performance metrics, turn-key operation and a compact footprint. In particular, ultrafast lasers based on emerging new materials in wavelength regimes with limited commercial available products (around 2μm wavelengths and longer) can fuel advances in biomedical imaging, infrared nerve stimulation and temporal characterization dynamics
Customized, compact fiber lasers
Customized and novel laser designs for fiber lasers are studied, in particular with an interest in high repetiton rate, fundamentally mode-locked ultrafast lasers. We are interested in investigating novel ultrafast laser operating regimes and understand how we can improve the laser design and stability. An innovative dual output pulse laser with interlaced ultrafast pulses from a single fiber laser has been demonstrated of interest for high precision, dual comb spectroscopy. Research opportunities span from modeling and simulation to experimental design, development and characterization.
Mid-infrared sources for novel applications
The ‘molecular fingerprint’ region around 2-10μm is particularly interesting for spectroscopy, gas tracing and environmental sensing applications since many molecules exhibit their fundamental vibrational resonances in the mid-IR. In addition, this eye-safe wavelength regime holds a deep potential for free-space optical communications as well as for medical treatment and diagnostics. Currently, only limited sources at these wavelengths exist.
Our goal is to develop compact, broadband and tunable sources as well as frequency combs in the mid-infrared region. Different technologies from fiber systems to nonlinear frequency conversion are investigated for continuous-wave and pulsed laser sources. One particular focus is on innovative thulium ultrafast fiber laser systems. Research opportunities range from fundamental material characterization, design and experimental development to higher level system engineering of sensors and communication technology.
Photothermal spectroscopy in the mid-infrared offers a label-free, non-destructive method for chemical identification based on inherent vibrational bond signatures. The developed mid-IR photothermal imaging system supersedes challenges associated with existing mid-infrared spectroscopy techniques to improve sensitivity and specificity of molecular identification. In photothermal spectroscopy a pump beam gets absorbed by a sample and the resulting localized change in the index of refraction can be measured with a probe laser, operating at wavelengths far removed from the vibrational characteristic resonances. By combining a fiber laser probe lasers with a quantum cascade laser, we have developed a compact and eye-safe photothermal spectroscopy configuration to study characteristic absorption bands in the mid-IR by acquiring spectral data and hyperspectral images. A novel nonlinear regime offers a new way to characterize materials with strong enhancements in sensitivity and can provide enhanced spatial imaging resolution, below the mid-infrared diffraction limit of the pump beam.
We study and characterize chemical samples as well as biological tissue sections in a label-free manner to obtain insights into material composition, molecule configurations and potential links to various diseases. Research opportunities include laser development, system optimization, modeling, sample characterization and analysis.
Infrared Nerve Stimulation
Optical infrared neural stimulation offers a direct neuromodulation mechanism that is highly selective, features good spatial confinement combined with minimal invasiveness compared to established electrical modulation, and does not require genetic modifications as for optogenetics Optical stimulation has the benefits of high selectivity, high spatial resolution, and no direct contact with the tissue, which reduces the inflammation risk.
The research project is focused on exploring and characterizing optical pathways for external neurostimulation. Novel optical systems will be investigated to stimulate nerves and conduct electrophysiology measurements. The aim is to obtain an enhanced understanding of the underlying biophysical mechanisms of infrared nerve stimulation with the potential for new therapeutic approaches for neurological diseases, neural control and pain management.
Micro-machining with an ultrafast laser system allows for more precise material removal and reduced thermal damage to the surrounding material, making this technique very attractive for material manipulation. Minimization of surface damage combined with cleaner cuts, and minimized residual heating gradients from the femtosecond laser can be of particular advantage for sample patterning with high precision. In addition, there is no risk of contamination by other chemicals as could occur during lithography steps or chemical etching.
This research project focuses on optimizing material ablation parameters and studying how spectroscopic observable parameters are connected to electronic structure and atomic arrangements, in particular for two-dimensional materials like graphene.