Time Resolved Optical Spectroscopy

Time Resolved Optical (TRO) Spectroscopy

Photomultiplier tube (PMT) detector (single frequency detection)

A diagram of the TRO system is shown below. The pump source is a NY-61 Nd:YAG laser manufactured by Continuum. Power is attenuated to approximately 20 mJ/pulse for the third harmonic (355 nm). The repetition rate is programmable from a single shot to 2, 4, 5, 10 and 20 Hz with 2 Hz being the most commonly used for these experiments. A 300 W xenon arc lamp from ILC Technology supplied the light for the probe. For kinetic traces, the output of the probe is first passed through an IR filter (water) and then through a SPEX single monochromator with the slits wide open. A band pass filter is substituted for the single monochromator for some of the studies in order to facilitate switching to CCD detection. A shutter is placed after the monochromator so that the probe beam could be shut off when data was not being taken. This configuration ensured that probe induced photochemistry will be kept to a minimum. The probe is focused into the sample and finally through a SPEX Model 1680 double grating monochromator and onto a RCA IP28 photomultiplier tube. The temporal response is recorded on a Tektronix TDS 540 digital oscilloscope which is linked to a 50 MHz 486 PC. Transients are commonly recorded as 100 shot averages with the best results being observed when the pump and probe beams are collinear to each other instead of perpendicular. Alignment of the system is checked prior to each experiment by optimizing the signal of ZnTPP at 450 nm. The optical arrangement allows one to very quickly change from using a PMT detector to a CCD detector. This is accomplished by focusing into a fiber optic which is placed in front of the double monochromator.

Charge Coupled Device (CCD) Detector

Similarly the spectral response is obtained by passing the probe beam (all wavelengths) through the sample then focusing into a fiber optic coupled to a SpectraPro-275 triple grating spectrograph which illuminates an intensified Princeton Instruments liquid nitrogen cooled 1024 -EUV CCD detector. The probe light is gated by a PG-200 Programmable Pulse Generator using an MCP intensifier as the gate source. The intensifier is red/blue enhanced to improve performance in the UV and red region of the spectrum. The CCD is an array of pixels (1024x256) with the wavelength being dispersed across the 1024 pixels. In order to optimize the speed of data collection the software allows for the 'binning together of many pixels to form one 'super' pixel which is read. All spectra are normally recorded using a single beam configuration, however, the system is equipped with bifurcated fiber optics cables which allows for both reference and sample to be collected at once. The standard procedure for constructing a transient spectrum is first to accumulate a reference spectrum taken with the laser off, (Io). Finally the sample is collected at a predetermined time after the laser has been fired and a duration equal to the reference with laser on, (It).

Three dimensional spectra consisting of Change in Absorbance vs. time vs. wavelength are constructed by obtaining transient difference spectra at many different time delays. When using a bifurcated cable the Io and It can be collected at the same time. In this case the probe beam is split into two beams and the differing amount of light must be accounted for by equating a region of the spectra with no absorbance changes.

Time resolved spectrum of Fe^III(TMPS) + NO as recorded by CCD camera.

High Pressure Measurements

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Time Resolved Optical (TRO) Spectroscopy

Photomultiplier tube (PMT) detector (single frequency detection)

	A diagram of the TRO system is shown below. The pump source is a NY-61 Nd:YAG laser manufactured by Continuum. Power is attenuated to approximately 20 mJ/pulse for the third harmonic (355 nm). The repetition rate is programmable from a single shot to 2, 4, 5, 10 and 20 Hz with 2 Hz being the most commonly used for these experiments. A 300 W xenon arc lamp from ILC Technology supplied the light for the probe. For kinetic traces, the output of the probe is first passed through an IR filter (water) and then through a SPEX single monochromator with the slits wide open. A band pass filter is substituted for the single monochromator for some of the studies in order to facilitate switching to CCD detection. A shutter is placed after the monochromator so that the probe beam could be shut off when data was not being taken. This configuration ensured that probe induced photochemistry will be kept to a minimum. The probe is focused into the sample and finally through a SPEX Model 1680 double grating monochromator and onto a RCA IP28 photomultiplier tube. The temporal response is recorded on a Tektronix TDS 540 digital oscilloscope which is linked to a 50 MHz 486 PC. Transients are commonly recorded as 100 shot averages with the best results being observed when the pump and probe beams are collinear to each other instead of perpendicular. Alignment of the system is checked prior to each experiment by optimizing the signal of ZnTPP at 450 nm. The optical arrangement allows one to very quickly change from using a PMT detector to a CCD detector. This is accomplished by focusing into a fiber optic which is placed in front of the double monochromator.






Charge Coupled Device (CCD) Detector

Similarly the spectral response is obtained by passing the probe beam (all wavelengths) through the sample then focusing into a fiber optic coupled to a SpectraPro-275 triple grating spectrograph which illuminates an intensified Princeton Instruments liquid nitrogen cooled 1024 -EUV CCD detector. The probe light is gated by a PG-200 Programmable Pulse Generator using an MCP intensifier as the gate source. The intensifier is red/blue enhanced to improve performance in the UV and red region of the spectrum. The CCD is an array of pixels (1024x256) with the wavelength being dispersed across the 1024 pixels. In order to optimize the speed of data collection the software allows for the 'binning together of many pixels to form one 'super' pixel which is read. All spectra are normally recorded using a single beam configuration, however, the system is equipped with bifurcated fiber optics cables which allows for both reference and sample to be collected at once. The standard procedure for constructing a transient spectrum is first to accumulate a reference spectrum taken with the laser off, (Io). Finally the sample is collected at a predetermined time after the laser has been fired and a duration equal to the reference with laser on, (It).
	Three dimensional spectra consisting of Change in Absorbance vs. time vs. wavelength are constructed by obtaining transient difference spectra at many different time delays. When using a bifurcated cable the Io and It can be collected at the same time. In this case the probe beam is split into two beams and the differing amount of light must be accounted for by equating a region of the spectra with no absorbance changes.
Time resolved spectrum of Fe^III(TMPS) + NO as recorded by CCD camera.

High Pressure Measurements

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