|
Optical Instrumentation
Optical methods of investigation of chemical systems are numbered among the oldest and newest of techniques. Consonant with the importance of the use of light in understanding chemical phenomena, the department has state-of-the-art instruments which range from traditional spectrophotometers, covering the spectral range from the ultraviolet to the infra-red, to one-of-a-kind instruments such as a three-circle Brillouin light-scattering apparatus. A large complement of linear and non-linear optical instrumentation provides the department with capabilities for optical measurements which few institutions its size can match. Linear optical studies involve both spectroscopic and light-scattering techniques. Capabilities for the former are, in addition to traditional instruments (one of which has a resolving power of 50,000): FTIR spectrometers ( from near to far-IR, i.e. 10,000 to 6 cm-1 ), microspectro-photometers, photoacoustic spectrometer, emission spectrometers, and piezomodulation spectro-meters. Several of these are specially modified for measurement of the anisotropy of macro-molecular systems and/or crystals. Many of these measurements are made at low temperatures, some as low as 2 K. Some of the instruments are unusual, such as the SLM multi-harmonic phase fluorometer and the OLIS rapid scanning monochromator used to study rapid reactions and grazing incidence and attenuated total reflection (ATR) FTIR for the study of films. Nonlinear optical techniques employing second harmonic generation and the Pockels effect are used with special focus on investigation of non-linear optical materials. Hyper-Raman and Hyper-Rayleigh scattering instruments are employed, for example, in determining first hyperpolarizabilities of non-linear chromophores. Time-resolved techniques exploit the great power of optical measurements to monitor events that occur on short time scales. Such experiments are capable of measurements of processes that occur down to femtosecond (10-15 s) times. The department has a wide selection of such time-resolved spectroscopies: Raman, fluorescence, second-harmonic generation, and absorption. Measurements span intervals from milliseconds to femtoseconds. Laser facilities are necessary for such time-resolved instrumentation. These have extensive application not only in time-resolved measurements but also in light scattering measurements. Again, the department has a great breadth of capabilities in these areas. A panoply of laser systems are employed: Nd:YAG, Ti:Sapphire, Ar ion, He-Ne, N2, and He-Cd. In addition to methods already mentioned, the laser-induced holographic grating relaxation technique is used to study molecular dynamics such as the translational diffusion of dye molecules dissolved in host amorphous polymer matrices. Laser light scattering is a sophisticated technique that is used to study the orientation and motions of both small and macromolecules in fluid and solid phases. State-of-the-art linear and non-linear light scattering instrumentation are found in the department. Both elastic ( Rayleigh, hyper-Rayleigh, static and dynamic) and inelastic ( Brillouin, Raman and hyper-Raman ) light scattering capabilities are represented. We believe the department is unique in its span of light-scattering techniques. While these optical methods may be viewed separately, it should be noted that they often play an integral role in special research applications. For example, they form vital components of unique programs in the department which deal with linear and non-linear optical materials, rapid reactions of biochemical systems, optical properties of monolayers and solid state organic chemistry. |
|
Please e-mail comments or suggestions about this site to the web server administrator. Department of Chemistry, University of Nebraska-Lincoln, Lincoln NE 68588-0304 |