Facilities

The Wasielewski Group is housed in Ryan Hall, the Nanofabrication Building completed in 2002. This facility has 44,000 net square feet of state-of-the-art research space designed for the demanding laboratory work required to advance the field of nanotechnology. The Wasielewski group occupies approximately 6,000 square feet of laboratory and office space in this facility.

Synthesis Laboratories

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The Wasielewski Group is well-equipped to carry out synthetic chemistry procedures in 17 6-foot fume hoods. A separate hood has a Glas-Contour column solvent purification system.

 Instrumentation rooms adjacent to the synthesis laboratories house bench top equipment, such as Shimadzu UV-VIS spectrophotometers, a PTI spectrofluorimeter, a CH Instruments Model 660 electrochemical analysis system, a Shimadzu GC system, as well as analytical (Agilent) and preparative (Waters) HPLC equipment, MBraun inert atmosphere glove boxes, and a high vacuum line.

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Electron Paramagnetic Resonance (EPR) Laboratory

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Our EPR lab offers the most updated EPR spectrometers for steady state and time resolved EPR measurements including CW EPR/ENDOR, Time-resolved CW EPR, Pulsed EPR experiments such as field-sweep echo-detected (FS-ED), ESEEM, ENDOR, ELDOR and coherent ELDOR.

Our lab is equipped with Bruker E-680X/W Pulse-EPR Spectrometer System with cryostats for operation down to 2K. This spectrometer can operate at CW and in Pulse modes at X-band (9.5 GHz) as well as W-band (94 GHz). In addition we have another Bruker E-580X that can operate in CW and Pulse modes at X-band (9.5 GHz) frequencies.

We also have a new state of the art home spectrometer operating at Ka-band frequencies (35 GHz). This spectrometer can operate at CW and Pulse modes and has a MW output of maximum 10 W at the resonator and allow us to give short pulses up to 10ns for p/2 pulses. The MW-bridge is equipped with two phase locked MW sources for coherent ELDOR experiments.

For sample excitation the lab is equipped with two Quanta-Ray nanosecond Nd-YAG/OPO laser systems.

We have designed and constructed a window-interfaced EPR simulation package for simulating and fitting EPR data using MATLAB. The program was designed and constructed by Raanan Carmieli from various codes we had in our group written by Dr. Qixi Mi, Dr. Zachary E. Dance and Dr. Raanan Carmieli. Useful help was given by Dr. Chul Hoon Kim. The program is free for download and it is an open code so feel free to test, check the code and send us your comment for improvement. We continue to improve and add new features all the time. Currently we are working on adding ENDOR simulation and speed up calculation time by parallel computing. If you use this program please don’t forget to acknowledge us.

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Laser Laboratory

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The Wasielewski Group’s laser laboratory has three high repetition rate amplified Ti:sapphire lasers for femtosecond spectroscopy.

System 1 is equipped for femtosecond transient absorption spectroscopy.  Femtosecond pulses are derived from a commercial oscillator (Tsunami oscillator/Millenia cw pump, Spectra-Physics) laser which generates 80 fs pulses that are amplified by a regenerative amplifier (Spitfire, Spectra-Physics).  This results in a 1 kHz pulse train of 120 fs, 827 nm pulses with a pulse energy of ~ 1 mJ.  The second harmonic of these pulses is split and used to drive two optical parametric amplifiers capable of generating optical pulses at 480-2400 nm.  A small fraction of the fundamental is focused into a sapphire plate for supercontinuum probe generation (450-800 nm).  The overall temporal resolution of the system is ~150-300 fs across the detectable range.  Dispersed spectra are collected as a function of pump-probe delay on a fiber-coupled CCD array (SD2000 ,OceanOptics, Inc.).

System 2 is equipped for femtosecond transient visible/mid-infrared absorption spectroscopy.  The laser also employs a commercial oscillator (Tsunami oscillator/Millenia cw pump, Spectra-Physics), configured for 20 fs pulses centered at 800 nm.  A regenerative amplifier (Spitfire, Spectra-Physics) is employed to amplify these pulses to ~1 mJ/pulse at 1 kHz with a ~50 fs pulse width.  The fundamental pumps two optical parametric amplifiers (TOPAS-C, Light-Conversion, Ltd.): the output of one is produces the visible pump (470-750 nm) while the output from the second creates the mid-IR probe (2000-6000 nm).  The resulting time resolution is ~100-300 fs. Spectra are dispersed and detected on  an array MCT detector. (Triax 190, Jobin Yvon/Horriba and Infrared Systems 2×64-pixel MCT array detector).

System 3 is configured for femtosecond transient absorption spectroscopy and femtosecond stimulated Raman spectroscopy (FSRS).  This laser system is based on a commercial femtosecond oscillator (Mai-Tai oscillator/Millenia cw pump, Spectra-Physics) producing 15 fs pulses at 800 nm.  These pulses feed a regenerative amplifier (Spitfire Pro XP, Spectra-Physics)  to yield a 1 kHz train of , 4 mJ, 35 fs pulses centered at 800 nm.   The fundamental is split to create the three pulses necessary for the FSRS experiment.  The actinic pump is created using a femtosecond optical parametric amplifier (TOPAS-C, Light-Conversion, Ltd.) for 460-3000 nm light.  The spectrally narrow Raman pump is generated by pumping another optical parametric amplifier (TOPAS-400, Light-Conversion, Ltd.) with the output of a second harmonic bandwidth compressor (SHBC, Light-Conversion, Ltd.).  This results in a near transform-limited picodsecond Raman pump pulse (460-700 nm) with ~10 cm-1 energy resolution.  The probe is generated by focusing a small fraction of the 800 nm fundamental into a sapphire plate to yield a broad supercontinuum (400-800 nm).  The temporal resolution is dictated by the cross-correlation of the two femtosecond pulses, about 50-300 fs across the detectable range.  Spectra are dispersed on the appropriate grating depending on the experiment and collected as a function of delay on a CCD array (Triax 180, Jobin Yvon/Horriba and PIXIS-100, Princeton Instruments).

A fourth high-repetition rate (100 kHz) amplified Ti:sapphire system is currently under construction for ultrafast microscopy experiments on solid samples.

In addition, a cavity-dumped femtosecond Ti-sapphire oscillator provides 25 fs, 800 nm pulses at a variable repetition rate (10s of kHz) that is frequency doubled. This laser system is used principally for time-resolved fluorescence measurements. A streak camera (Hamamatsu, Streakscope) is used to determine time-resolved fluorescence spectra with a time resolution of about 5 ps.  Faster time scale measurements down to 50 fs are made using fluorescence up-conversion techniques.

Nanosecond transient absorption and emission measurements are made using a Q-switched Nd:YAG laser at 10 Hz with 7 ns pulse width (Precision II 8000, Continuum).  The excitation pulses are derived from an optical parametric oscillator (Panther, Continuum) pumped with the third harmonic of the 1064 nm fundamental.  The full spectrum of a Xe flash-lamp is used as the probe for pulsed measurements (out to ~6 microseconds), while a cw Xe arc-lamp is used to measure transient absorption into the millisecond regime.

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The Wasielewski Group
at Northwestern University
2190 Campus Dr., Ryan Hall, Room 1010
Evanston, IL 60208
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