Terahertz spectroscopy

High-speed cameras capture cavitation bubble collapse, shock waves and supersonic microjets at up to millions of frames per second. Femtosecond laser pulses both trigger these events and provide illumination short enough to freeze sub-microsecond motion that conventional imaging cannot resolve.

Laser-induced plasma serves elemental analysis, thin-film deposition and short-wavelength light generation. LIBS identifies solid, liquid or gaseous samples in-situ, pulsed laser deposition grows films in a vacuum chamber, and laser-produced plasmas emit EUV and soft X-rays for lithography, metrology and microscopy.

Laser flash photolysis captures short-lived intermediates of photo-induced reactions: a pump pulse from a pulsed laser generates excited states, radicals and ions, and a probe pulse records their transient absorption on nanosecond and shorter timescales. Broadly tunable OPO lasers cover the pump wavelengths these experiments require.

SFG vibrational spectroscopy resolves molecular vibrations at surfaces and interfaces, where broken inversion symmetry allows a sum-frequency signal that bulk media forbid. Mixing a tunable infrared beam with a visible beam yields a signal in the visible range, measured with PMT or CCD detectors on scanning or broadband SFG spectrometers.

SHG probes surfaces and interfaces where inversion symmetry breaks: measurements reveal surface coverage, molecular orientation, adsorption-desorption processes and interfacial reactions, while SHG microscopy images collagen, myosin and other polar filament systems in tissue without labels.

Pump-probe spectroscopy follows dynamics directly: a pump pulse excites the sample and a delayed probe pulse records the change, mapping excitation relaxation, energy transfer, reaction dynamics and structural motion. Tunable pump and probe wavelengths extend the method to two-dimensional energy maps of coupled states.

Time-resolved photoluminescence follows how excited charge carriers relax in a solid: a pulsed laser excites the sample and the emission decay is recorded against time. The decay curves give carrier lifetime, recombination pathways and defect states in semiconductors, thin films and optoelectronic materials.

Ions trapped in vacuum give intrinsic electronic transition energies, free of the shifts a solvent or matrix imposes. Electrosprayed ions are mass-selected in a Paul trap, excited by a tunable pulsed laser, and their emission is dispersed onto a CCD spectrometer. The same setup resolves gas-phase biomolecular structure through FRET.

Supercontinuum generation turns a narrowband pulse into white light spanning 400 nm to 2400 nm, broadened by nonlinear processes in a photonic crystal fiber or waveguide. Picosecond pump sources drive the process, and a tunable filter carves the continuum into a widely tunable source for imaging, spectroscopy and device characterization.

A light pulse raises a material’s conductivity, and the decay that follows carries the physics: carrier density, mobility, trapping and recombination. Time-resolved photoconductivity reads that decay through electrodes or, at microwave frequencies, without contacts, and is applied to organic and inorganic semiconductors, dyes and metal-insulator composites.

Z-scan measures the nonlinear optical response of a material by translating it through a focused laser beam and recording the transmitted power against position. The closed-aperture scan gives the nonlinear refractive index behind the Kerr effect; removing the aperture gives the nonlinear absorption coefficient, dominated by two-photon absorption.

A LIDAR fires short laser pulses into the atmosphere and times the light that scatters back off aerosols, dust and air molecules. Each return maps to a distance, so a single pulse profiles the whole beam path. Tuning the wavelength onto a molecular absorption line turns that range profile into a concentration profile.

A focused laser pulse vaporizes a microscopic amount of the sample and lights it as a plasma. Every element in that plasma emits at its own wavelengths, so a spectrograph reading the flash identifies what the material is made of, in seconds and without touching it, on solids, liquids and gases alike.