Schematic diagrams of the pulse ordering of optical 2DFT techniques available with a three-pulse excitation scheme: (a) represents the “rephasing” technique, (b) is a variant of (a) where the middle time axis is scanned to examine nonradiative contributions, (c) is “nonrephasing” technique, and (d) is the two-quantum technique. In each case, axes 1 and 2 are labeled for comparison to the inset of (a) showing which axes are plotted in the resulting 2DFT spectrum.
Schematic representation of the nested Michelson interferometer layout. , B, C, and Ref are the Ti:sapphire laser pulses used to perform the 2DFT experiment. The HeNe laser beam is reflected from the DCM to provide diagnostic information for the interferometers. The proposed layout is folded such that the DCM is a common optical element.
CAD drawings of the JILA-MONSTR’s (a) lower and (b) upper interferometer decks. P refers to the periscope between decks and R indicates the right-hand side on each deck. Laser input is on the left side of the lower deck and the Ti:sapphire pulses emerge from the front through the DCM, two from each deck. Error signals for each interferometer emerge from the right-hand side as dashed lines, two from the bottom, and one from the top decks. (, plate, transducer, and photodetector.) (c) Three-dimensional CAD drawings of the entire assembly showing how the two decks are combined.
Photograph of the JILA-MONSTR highlighting the input beam on the right-hand side of the picture and four output beams focused to a single location.
The error signals for the top-deck, bottom-deck, and interdeck interferometers recorded for approximately 10 min (a) without and (b) with active stabilization engaged. In (a) circles link each trace to the appropriate label. In (b) the bottom-deck and interdeck signals are offset from zero for presentation purposes.
Experimental setup for 2DFT spectroscopy showing the pump and phase stabilization laser, the JILA-MONSTR with diagnostic port, and feedback loops. Also shown are the arrangement of the sample and the collection of light in the spectrometer. A heterodyne reference pulse is used to perform spectral interferometry and reconstruct the time axis . The inset shows a typical spectral interference pattern recorded for the quantum well sample.
(a) Flow chart of the stepping algorithm to ensure identical steps. There are several measurements of the error signal: occurs before (after) unlocking the loop filter and is measured after the stage has been moved. is half the maximum peak-to-peak error signal, is maximum attempts to wait for the error signal to obtain a value within (near zero), and is the total number of spectrum acquired in the 2DFT scan. (b) A typical screen capture of the oscilloscope that monitors the error for the top-deck interferometer while it is being scanned 4 HeNe fringes. The shaded regions mark when the feedback loop is engaged.
[(a) and (d)] Linear absorbance spectrum of the GaAs quantum well sample. Dashed lines show the excitation laser spectra. 2DFT spectra of GaAs quantum wells, showing (b) nonrephasing , (c) rephasing , and (e) two-quantum techniques. The 2DFT spectra are normalized to the strongest feature, and the thicker contour line encloses the regions of the negative signal. All 2DFT spectra are for excitation. The single-quantum [(b) and (c)] and two-quantum (e) spectra are acquired for cocircular and cross-circular excitation, respectively.
(a) Schematic method of the phase cycling operation for 2DFT spectroscopy. While a time delay is scanned, pulses C and Ref are simultaneously toggled back and forth by and two spectral interferograms are recorded per data point. (b) Shows the Fourier transform of the recorded spectral interferograms taken when and are approximately 1 ps. The dashed line is a result of a single interferogram (i.e., normal operation) and the solid line is for the difference of the two interferograms. The inset shows the stepped slope of the scanned pulse and the toggled pulses C and Ref.
An example of noise reduction in the 2DFT spectra of vapor using phase cycling. The left-hand panels show rephasing and nonrephasing spectra obtained through normal operation, and the right-hand panels use phase cycling of the C and Ref pulses by 6 HeNe fringes.
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