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Advanced Optical Spectroscopy and Microscopy


The Advanced Optical Spectroscopy & Microscopy Facility combines a broad range of optical instruments suitable for studies of optical properties of hard, soft or biological materials using ultrafast and nonlinear spectroscopy, and single-molecule optical and confocal methods.


  • Fluorescence imaging (up to five channels simultaneously), two-color fluorescence lifetime imaging, spectral imaging, and fluorescence correlation spectroscopy
  • Fluorescence lifetime measurements, including time-resolved fluorescence anisotropy and time-resolved fluorescence spectra, using single-photon counting and fluorescence upconversion methods
  • Single-molecule spectroscopy: fluorescence intensity, lifetimes, anisotropy and fluorescence spectra
  • Transient absorption and reflectivity spectroscopy: broadband femtosecond and nanosecond probes covering UV, VIS and NIR; two-color low temperature pump-probe spectroscopy
  • Z-Scan measurements of optical nonlinearities: open and closed aperture with tunable excitation wavelength
  • Advanced data analysis methods, including single decay and global fits using a variety of kinetic models

Ultrafast and Nonlinear Spectroscopy

Contact: Matthew Sfeir

Our facility houses a state-of-the-art high power kilohertz femtosecond regenerative amplifier combined with an optical parametric amplifier that allows generation of sub 100 femtosecond pulses in the ultraviolet, visible, and infrared regions of the spectrum. This system is coupled to a series of user-friendly time-resolved and nonlinear optical techniques, providing Users with a broad suit of tools for characterizing the photophysical properties of their materials, including:

Femtosecond Transient Absorption Spectroscopy

The CFN houses a broadband transient absorption spectrometer with approximately 100 fs time resolution in a time window of 0 - 3 ns.  In this technique, the samples are optically "pumped" using a tunable (240 - 2600 nm) femtosecond laser pulse and "probed" for changes in transmission using a "white-light" laser generated supercontinuum.  The system can be configured to record spectral transients in one of three operating modes: 350 - 700 nm, 450 - 820 nm, or 800 - 1600 nm.  Sample holders for cuvettes and thin films are available.

Nanosecond Transient Absorption Spectroscopy

In addition, the broadband transient absorption spectrometer can be configured to measure long-lived electronic and chemical species with sub-ns time resolution in a time window of 0 - 50 microseconds. In this configuration, spectral transients can be recorded in one of two operating modes: 370 - 900 nm or 800 - 1700 nm.  Sample holders for cuvettes and thin films are available.  This is an optically gated technique using a femtosecond excitation pulse and a longer (~ 500 ps) white-light laser probe pulse.

Fluorescence Upconversion Spectroscopy

This spectrometer is able to measure ultrafast emission processes in the visible and NIR (400 - 1600 nm) with a time resolution of ~ 100 fs in a time window of 0 - 3 ns.  In the upconversion method, the emitted photons are mixed with an optical gate pulse in a nonlinear crystal optimized for sum frequency generation.  We detect the intensity of the higher energy upconverted photons as a function of time delay between the excitation pulse and the gate pulse to map out the kinetics. Alternatively, spectral emission transients can be recorded at a fixed delay time.  For longer kinetic processes, the spectrometer can also be operated in time-correlated single photon counting mode (TCSPC) in which the emitted photons are directly detected.  The use of fast electronics allows for a time resolution of 100 ps over a range of 0 – 1 ms.

Z-Scan Measurements for Determining Optical Nonlinearities

We have implemented this technique for measuring multi-photon absorption coefficients and nonlinear refractive indices of novel photonic materials.    In this experiment, a thin solid or liquid sample is translated through the focus of high pulse energy NIR light (700 – 1200 nm).  The normalized transmission is detected as a function of position along the light focus and used to derive the nonlinear optical coefficients.

Single Molecule Optical and Confocal Methods

Contact: Mircea Cotlet

Multiparametric time- and spectrally-resolved confocal single molecule fluorescence microscopy

Open frame scanning-stage confocal fluorescence microscope based on Olympus IX81 frame interfaced with a broad-band ultrafast laser system (350-670nm tunable, 85 fs, variable repetition rate). Based on a 1.4 NA oil lens, a 100x100 microns range piezo-scanner, four single photon counting avalanche photodiodes (simultaneous two color & polarization  single molecule detection), PicoHarp 300 timing analyzer, attached spectrometer (Acton 2300) with back-illuminated CCD for fluorescence and Raman spectroscopy. The instrument is capable of measurements of single molecule fluorescence lifetimes (100 ps resolution), intensity, FLIM, time-resolved fluorescence and Raman spectroscopy.  May be interfaced with atomic force microscope (NanoSurf).

Two-color Fluorescence Correlation Spectroscopy

Open frame confocal fluorescence microscope based on Olympus IX71 frame interfaced with several CW lasers (457-514nm Ar-ion tunable, He Ne 543, 594 and 632nm). Based on a 1.2 NA 60 water or 1.45 NA, 60 oil immersion lens, two avalanche photodiodes, PicoHarp 300 timing analyzer. The instrument in capable of two-color excitation, two-color detection and cross-correlation FCS, antibunching.

Total internal reflection fluorescence microscopy

TIRF microscope based on Olympus IX81 frame. Uses a through-objective 1.45 NA oil immersion lens, an electron-multiplying (EMCCD) camera, dual view optical detection for FRET and colocalization studies. Uses three laser lines (488, 561 & 632nm) combined or alone, include bright field, darkfield, differential interference contrast, 2D-single molecule tracking software. Diffraction-limited spatial resolution.

Leica SP5 confocal laser scanning fluorescence microscope for fast imaging

Commercial confocal microscope based on a DM6000 frame interfaced with continuous wave lasers (457, 488, 514, 543 and 632nm lines). Includes several lenses, 1.2 NA 63x water, 1.4 NA 63x oil, AOBS (optical filter free) for spectral detection, 3 detection channels for fluorescence (PMTs), one for transmission (DIC, Polarized). Time-lapse confocal imaging, FRET, FRAP, FCS, Hyperspectral Imaging, low signal imaging with avalanche photodiodes.