Laser Laboratory
Picosecond Transient Absorbance Equipment
"Continuum end" of the picosecond TA kinetics laser table in experimental bay one. The right side of the picture shows the granite mounted, Anorad delay line with a retroreflector prism on its translation stage. The air-bearing controlled translation stage varies the light path of the 355-nm excitation beam and produces experimental delay times ranging from -300 ps (before sample excitation) to +15.5 ns (when the stage is moved fully to the other end of the granite support). Intense 532-nm laser pulses are focused into the 20-cm long liquid cell in the center of the picture to produce continuous probe wavelengths ("continuum light") from 360 - 750 nm.
The PC and CAMAC instrumentation used to operate the picosecond transient absorbance (TA) kinetics system in experimental bay one. The PMT pulse shapers and laser control electronics were custom designed and built and Brookhaven National Laboratory. All of the experiment's control software was developed in Dr. Netzel's laboratories.
"Sample end"of the picosecond TA kinetics system in experimental bay one. In this picture the control electronics are to the right in a CAMAC crate and the Anorad delay stage is to the left. The "flowing" sample cell is located just behind the pre-amplifier electronics that are suspended from an overhead shelf. Normally the sample monochromator is located under the pre-amplifier and behind the sample cell, however, here it is located on the right edge of the laser table to permit easy lubrication of its grating drive shaft.
Dr. Samir Gaballah adjusting a mirror that directs 532-nm light from the Nd/YAG laser in experimental bay two to the front of the granite delay line of the picosecond TA kinetics system in experimental bay one. Probe light (25-ps duration) from 360 - 750 nm is generated at the other end of the laser table by focusing the 532-nm light into a 20-cm long cell filled with a mixture of H20 and D20.
Nd/YAG Laser System
The Continuum, Inc. active-passive mode-locked Nd/YAG picosecond laser system in experimental bay two. This versatile laser system has four output beams whose energies are independently controlable for use in up to three, simultaneously operating laser experiments. Typically, three of these beams are regular use: two for TA kinetics and one for time-resolved emission kinetics. The fourth beam is available as as a reserve beam and for setting up new experiments.
Dr. Samir Gaballah adjusting a fast photodiode used to tune the degree and stability of the mode-locking of the Continuum, Inc. picosecond laser system in experimental bay two. The Tektronix oscilloscope behind Dr. Gaballah has an intensified CRT to display the individual mode-locked pulses in a laser train. Each flashlamp firing of the Nd/YAG laser produces a single train of eight laser pulses, each of 30-ps duration and separated from each other by the round-trip time of the laser oscillator's cavity (6.6 ns). Each pulse appears on the oscilloscope to have a 1-ns rise time due to the response-time limit of the fast photodiode. A Pockels cell in on the laser table, near the oscilloscope extracts the maximum-energy pulse of each laser train for amplification and use in kinetics experiments. The other seven laser pulses in each train are discarded.
Picosecond Emission Kinetics Equipment
Dr. Netzel editing a data acquisition program for the picosecond emission kinetics system in experimental bay three. The large beige box directly in front of Dr. Netzel is a Tektronix SCD1000 digitizer. The excitation beam for the emission kinetics experiment comes to the laser table in bay three from the Continuum, Inc. laser system in bay two that is in the background of this picture. The shiny cylinder in the background between Dr. Netzel and the SCD1000 is the Hamamatsu microchannel plate detector used for short (< 20 ns) emission lifetime measurements. For longer lifetime measurements (20 ns - 100 ms) a Hamamatsu R928 PMT is used.
Nanosecond Laser Kinetics Equipment
Dr. Yasser Hussein adjusting the optics in the Continuum, Inc. ND6000 nanosecond dye laser in experimental bay four. The wavelengths of the ND6000 and the UVT harmonic generator are controlled by the PC that is mounted on the shelf over the laser table. The Continuum, Inc. ND6000/UVT laser system produces pulses of 6-ns duration at a variable rate of up to 10 Hz. The Edinburgh Instruments LP920 nanosecond kinetics system is located on the far side of the laser table.
Dr. Yasser Hussein preparing to put a sample into the sample chamber of the Edinburgy Instruments LP920 nanosecond laser kinetics system. The LP920 is capable of making both emission lifetime and transient absorbance kinetics measurements. Also, the LP920 can make these measurements one wavelength at a time with a PMT detector or over a 270-nm spectral range at one time with ICCD camera. The camera is located to Dr. Hussein's right, where it is attached to the LP920 system's monochomator.
This picture shows a close-up view of both the PMT and ICCD camera detectors. The camera can be operated with varying time windows (as short as 5 ns), gains, and delay times with respect to laser excitation. It is particularly useful for recording the TA spectra of samples that are either in short supply or that degrade upon photoexcitation. In such cases it would not normally be possible to acquire their TA spectra using only a PMT.
Dr. Yasser Hussein operating the Edinburgh Instruments LP920 kinetics system in experimental bay four. The Continuum, Inc. nanosecond Nd/YAG/dye laser system is on the far side of the laser table. The 6-ns laser excitation pulse (of nearly continuously variable wavelength from the near-IR to the UV regions) makes a U-turn at the right end of the laser table and enters the LP920 sample chamber (the large beige box to the left of Dr. Hussein) from the chamber's right side (in the middle of the table). The sample chamber is accessed by raising the round cover with the black handle on the top of the beige box.
Synthetic Laboratory Equipment
Mrs. Reham Abou-Elkhair cleaning out a silica gel column in the synthetic laboratory. Located to her right are Speed-Vac and Roto-Vap instruments for stripping solvent from sample solutions.
This Pharmacia FPLC system is located immediately behind Mrs. Abou-Elkhair in the previous picture. The FPLC system is used to purify covalently modified, single strands of DNA (ssDNA). Collected fractions are concentrated in the Speed-Vac on the opposite bench.
The above picture shows a hood mounted vaccum line with a sample being dried and the right side of a larger, general purpose vacuum line. Typical uses of these vacuum manifolds are drying and degassing samples and reagents prior to their use in, respectively, experiments and synthetic reactions.
This picture shows our Vacuum Atmospheres dry box (with its internal freezer) and the left side of the general purpose vacuum line. The dry box greatly facilitates handling the air- and water-sensitive solids and liquids used in many of our nucleoside syntheses, in assembling reference electrodes for electrochemical measurements, and in preparing oxygen-free samples for spectroscopic and kinetics study. The lower left side of this picture shows most of our PC-controlled Shimadzu UV-2501 UV-vis spectrophotometer. Not shown in any of the laboratory pictures is a second UV-vis spectrophotometric system located in the laser laboratory. The second UV-vis system is used for DNA melting experiments to measure the stability of labeled DNA duplexes prior to laser kinetics study.
Student and Postdoc Work Areas
This picture shows part of the office space for up to five graduate students and postdocs. On the wooden desk is Mac G3 computer and on the metal desk to its right are an HP 4600 color laser printer and an SGI Origin 200 four-processor workstation. Both the printer and the Origin 200 are network mounted for access from any networked PC in our research group. The Origin 200 is used for MD and QM studies using software such as AMBER, SPARTAN, and GAUSSIAN.
Dr. Samir Gaballah smiles at the camera from his desk in the student/postdoc office area. His desk is located directly across from the Origin 200 computer shown above.
In addition to the laser and synthetic laboratories and the student/postdoc office area already shown, the Netzel group also has a workroom with open access computers for all group members. This pictures shows three of the four Dell 2.6 GHz PCs located in the workroom. These PCs are less than a year old and have both standard desktop and QM software loaded on them. The QM software includes Windows versions of SPARTAN, HYPERCHEM, GAUSSIAN, and GAUSSVIEW. These PCs can also be booted with the LINUX OS to run AMBER and related MD software for computational study of the dynamics of covalently modifed DNA duplexes. Also in this room are two networked printers, an HP 1300 b/w laser printer and an HP G95 four-in-one FAX/Scanner/Copier/Color InkJet Printer. All three of the groups printers are accessible from any of the group's office computers. The Chemisry and Biology departments also have networked large format, color laser printers for producing 3' x 5' (or longer) posters for presentation of research results at professional society meetings.