The Center for Laser and Optical Spectroscopy
Researchers within the Center for Laser and Optical Spectroscopy possess world-class laser facilities. A wide variety of laser equipment is present in the Center, having pulse-widths ranging from the femtosecond to nanosecond time-scale, and tunability from the ultraviolet to the near infrared.
Ultrafast spectroscopy experiments are performed with a regeneratively amplified femtosecond laser system consisting of a Coherent Vitesse oscillator, a Nd:YLF DQE pump laser, the regeneratively amplified/multipass laser, and three TOPAS optical parametric amplifiers. This laser system is used for transient absorption and fluorescence up-conversion experiments in the femtosecond regime. Condensed phase experiments measuring excited state lifetimes, energy and electron transfer, and one- and two-photon pump-probe absorption experiments are routinely performed using this laser system.
Experiments using on the picosecond time-scale are performed using a mode-locked picosecond Nd:YLF laser that pumps a Coherent 700 dye laser and is capable of producing 1 ps pulses over a range of wavelengths. A variety of condensed and gas phase experiments are performed using this laser system, such as time-correlated single photon counting (TCSPC) experiments to measure fluorescence lifetimes and changes in fluorescence anisotropy that are useful for determining volume changes in dendrimers and polymers as a function of changing environment. When used in conjunction with a three-stage dye amplified laser, rotational coherence experiments are performed on gas phase molecules and molecular clusters.
Five nanosecond Nd:YAG and excimer pumped dye laser systems within the center offer tunability in the nanosecond time-scale from the near infrared to the ultraviolet. Typical condensed-phase experiments on the nanosecond time-scale include laser flash photolysis experiments on short-lived reactive intermediates and excited states. Two-color, two-photon experiments on highly reactive intermediates and excited states in solution also are performed with these laser systems. Several nanosecond laser systems are used to carry out various pump-probe and pump-pump-probe experiments on jet-cooled gaseous molecules to study their excited-state dynamics.
The Center also has an Olympus microscope for performing single-molecule spectroscopy. Excitation for this system uses a diode laser (488 nm) and enables researchers to study fluorescent samples that are either free-flowing or fixed to a microscope slide.
The center has two single-frequency continuous-wave (less than a few megahertz bandwidth) ring lasers operating in the UV/Visible range. The ring laser is pulse-amplified by about a factor of 105 using a dye amplifier, to produce high-intensity light pulses with very narrow line widths. The pulse-amplified ring laser is combined with skimmed supersonic molecular beams of small Doppler widths to determine structures of van der Waals molecules. The structural information of the species also is probed by mass-resolved rotational coherence spectroscopy using the regeneratively amplified picosecond laser system and time-of-flight mass spectrometers. There are two single-frequency continuous-wave infrared laser systems that are used for high-resolution cavity-ringdown studies of molecular vibrations, torsions and rotations. These include a PPLN OPO and an external-cavity diode laser. Also available in the center is a FT-IR spectrometer that has a range in the mid-IR and near-IR, and has advanced features such as dual channel collection step-scan capabilities for polarization modulation (VCD, PMIRRAS) and time-resolved (20 ns) experiments.
Combined with several supersonic molecular beam apparati, the center has unique, state-of-the-art capabilities for probing elementary processes of importance in chemistry (i.e., electron-transfer, energy-transfer, energy dissipation, molecular motions, structural and chemical changes) that occur on a broad range of time scales.