Many important scientific questions in physics, chemistry and biology require effective methodologies to spectroscopically probe ultrafast intra- and inter-atomic/molecular dynamics. However, current methods that extend into the femtosecond regime are capable of only point measurements or single-snapshot visualizations and thus lack the capability to perform ultrafast spectroscopic videography of dynamic single events. Here we present a laser-probe-based method that enables two-dimensional videography at ultrafast timescales (femtosecond and shorter) of single, non-repetitive events. The method is based on superimposing a structural code onto the illumination to encrypt a single event, which is then deciphered in a post-processing step. This coding strategy enables laser probing with arbitrary wavelengths/bandwidths to collect signals with indiscriminate spectral information, thus allowing for ultrafast videography with full spectroscopic capability. To demonstrate the high temporal resolution of our method, we present videography of light propagation with record high 200 femtosecond temporal resolution. The method is widely applicable for studying a multitude of dynamical processes in physics, chemistry and biology over a wide range of time scales. Because the minimum frame separation (temporal resolution) is dictated by only the laser pulse duration, attosecond-laser technology may further increase video rates by several orders of magnitude.

In this work, the combustion behavior of seeded iron particles (d₅₀ = 70 µm) in a laminar diffusion flame was studied in a modified Mckenna flat-flame burner. Two high speed cameras in stereo configuration allowed 3D position and 3D velocity measurements of burning iron particles as well as 3D evaluation of particle microexplosions. Microexplosive processes are important since it can affect both combustion stability and formation of product components. The observed microexplosions happened before particle extinction resulting in change of trajectories, velocities, radiation intensities and fragmentation into smaller particles. It was observed for the first time that fragments of these microexplosions tend to produce planar structures. A frequent release phenomenon was observed during the iron particle combustion using magnified thermal radiation imaging and high-speed shadowgraphy. This release phenomenon was indirectly confirmed with scanning electron microscopy of combust products, revealing multiple cracked particle shells and hollow structures. Black body radiation characteristics was observed indicating the release being in condensed phase and emission spectroscopy identified FeO as intermediate species during combustion. The observed release is believed to mainly consist of iron-oxide nanoparticles formed in the homogenous reaction between vapor iron and oxidizers.