RESUMEN
Ultrashort mid-infrared pulses at a repetition rate of 82 MHz have been generated by difference-frequency mixing at the output of a single-cavity, two-color femtosecond Ti:sapphire laser. The center wavelengths of the midinfrared pulses are tunable from 7.5 to 12.5 microm. Their pulse durations range from 450 to 650 fs, as a function of the center wavelength.
RESUMEN
We demonstrate and characterize an apparatus for transient infrared spectroscopy with a 5-ps resolution. A visible pump and narrow-band mid-infrared probe are both derived from a source that is based on a pulsed Nd:YAG regenerative amplifier that operates at 540 Hz. We measure transient spectra in the range 1770-2250 cm(-1) with a 1-cm(-1) resolution and sensitivity to absorbance changes less than or equal to 1 x 10(-3). As an example, we present results from experiments to study ligand photodissociation from carboxymyoglobin in D(2)0.
RESUMEN
We report on time-resolved absorption studies of the bovine visual pigment rhodopsin with subpicosecond resolution at room temperature. Our data show that bathorhodopsin, rhodopsin's early photoproduct, is photochemically formed in 3.0 +/- 0.7 ps. The data suggest that bathorhodopsin formation is kinetically preceded by two species along the rhodopsin-to-bathorhodopsin reaction coordinate. The first is identified with the vertically excited Franck-Condon state. This decays with an approximately 200-fs lifetime to an intermediate, which then decays to bathorhodopsin in 3.0 ps. We assign this intermediate to be an excited state transient near 90 degrees along the 11-12 torsional coordinate of rhodopsin's chromophore. Exchange of rhodopsin's exchangeable protons for deuterons does not affect the observed dynamics. These observations are both qualitatively and quantitatively consistent with molecular dynamics calculations, which model the rhodopsin to bathorhodopsin phototransition as a cis-trans isomerization along the 11-12 torsional coordinate of rhodopsin's chromophore.
Asunto(s)
Rodopsina/química , Animales , Bovinos , Deuterio , Técnicas In Vitro , Isomerismo , Cinética , Fotoquímica , Rodopsina/análogos & derivados , Análisis Espectral/métodos , Factores de TiempoRESUMEN
Time-resolved infrared spectroscopy with 0.5-ps resolution is used to track the evolution of the CO stretching vibration after visible photoexcitation of carboxyhemoglobin in water at room temperature. Polarization measurements determine that the iron-complexed CO is oriented nearly perpendicular to the porphyrin plane. The dissociation appears to proceed via a metastable excited state with 2 +/- 1 ps lifetime. The dissociated CO binds weakly in the heme pocket for at least 500 ps. This state correlates with the internally bound state observed by Frauenfelder et al. at low temperatures in myoglobin.
Asunto(s)
Carboxihemoglobina/metabolismo , Carboxihemoglobina/efectos de la radiación , Humanos , Cinética , Ligandos , Fotólisis , Espectrofotometría Infrarroja/métodos , Factores de TiempoRESUMEN
A technique to record transient vibrational spectra with 0.5-psec resolution is reported. The apparatus is based on seeded optical parametric amplification. A study of the microscopic details of the photodissociation of carboxyhemoglobin is described as an example.
RESUMEN
We describe the generation of 350-fs pulses tunable between 2.3 and 5.5 microm by seeded optical parametric amplification. These pulses are synchronized with visible pulses for time-resolved absorption and reflectivity in semiconductors with 500-fs resolution.
RESUMEN
An apparatus to probe picosecond photoinduced absorption in semiconductors between 2 and 5 microm with picosecond resolution is described. The IR source is based on difference frequency mixing an amplified picosecond dye laser pulse with a synchronized white light continuum pulse. The choice of liquid for continuum generation is discussed, and applications to transient absorption in germanium and trans-polyacetylene are presented.
RESUMEN
A powerful data acquisition and control system at a very low cost is presented. This is made possible by providing the interfacing hardware and supporting software to integrate the new and low-cost consumer-marketed ''personal computers'' into a useful and powerful data acquisition system. This system can be configured to the user's need at any given time, simply by writing the appropriate software. In addition to its computing power, the system has been programmed for use as a transient digitizer-multichannel analyzer with a minimum of 12 microsec per channel, a data and curve fitter, a general x-y recorder and averager, and a general purpose lab equipment controller. The system developed is, in many respects, at least as powerful as a DEC-PDP 11/04 system--at a small fraction of the cost.