An official website of the United States government
BoxCARS and pump-probe geometries are common implementations of two-dimensional infrared (2D IR) spectroscopy. BoxCARS is background-free, generally offering greater signal-to-noise ratio, which enables measuring weak vibrational echo signals. Pulse shapers have been implemented in the pump-probe geometry to accelerate data collection and suppress scatter and other unwanted signals by precise control of the pump-pulse delay and carrier phase. Here, we introduce a 2D-IR optical setup in the BoxCARS geometry that implements a pulse shaper for rapid acquisition of background-free 2D IR spectra. We show a signal-to-noise improvement using this new fast-scan BoxCARS setup versus the pump-probe geometry within the same configuration.
more »
« less
Contrast mechanisms in pump-probe microscopy of melanin
Pump-probe microscopy of melanin in tumors has been proposed to improve diagnosis of malignant melanoma, based on the hypothesis that aggressive cancers disaggregate melanin structure. However, measured signals of melanin are complex superpositions of multiple nonlinear processes, which makes interpretation challenging. Polarization control during measurement and data fitting are used to decompose signals of melanin into their underlying molecular mechanisms. We then identify the molecular mechanisms that are most susceptible to melanin disaggregation and derive false-coloring schemes to highlight these processes in biological tissue. We demonstrate that false-colored images of a small set of melanoma tumors correlate with clinical concern. More generally, our systematic approach of decomposing pump-probe signals can be applied to a multitude of different samples.
more »
« less
- Award ID(s):
- 2108623
- PAR ID:
- 10369916
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 30
- Issue:
- 18
- ISSN:
- 1094-4087; OPEXFF
- Format(s):
- Medium: X Size: Article No. 31852
- Size(s):
- Article No. 31852
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We demonstrate fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) with a broadband, continuum probe pulse pair in the pump-probe geometry. The approach combines a pump pulse pair generated by an acousto-optic pulse-shaper with precise control of the relative pump pulse phase and time delay with a broadband, continuum probe pulse pair created using the Translating Wedge-based Identical pulses eNcoding System (TWINS). The continuum probe expands the spectral range of the detection axis and lengthens the waiting times that can be accessed in comparison to implementations of F-2DES using a single pulse-shaper. We employ phase-cycling of the pump pulse pair and take advantage of the separation of signals in the frequency domain to isolate rephasing and non-rephasing signals and optimize the signal-to-noise ratio. As proof of principle, we demonstrate broadband F-2DES on a laser dye and bacteriochlorophylla.more » « less
-
Ultrafast transient vibrational action spectra of cryogenically cooled Re(CO)3(CH3CN)3+ ions are presented. Nonlinear spectra were collected in the time domain by monitoring the photodissociation of a weakly bound N2 messenger tag as a function of delay times and phases between a set of three infrared pulses. Frequency-resolved spectra in the carbonyl stretch region show relatively strong bleaching signals that oscillate at the difference frequency between the two observed vibrational features as a function of the pump–probe waiting time. This observation is consistent with the presence of nonlinear pathways resulting from underlying cross-peak signals between the coupled symmetric–asymmetric C≡O stretch pair. The successful demonstration of frequency-resolved ultrafast transient vibrational action spectroscopy of dilute molecular ion ensembles provides an exciting, new framework for the study of molecular dynamics in isolated, complex molecular ion systems.more » « less
-
We present a novel, to the best of knowledge, time-resolved, optical pump/NIR supercontinuum probe spectrometer suitable for oscillators. A NIR supercontinuum probe spectrum (850–1250 nm) is generated in a photonic crystal fiber, dispersed across a digital micromirror device (DMD), and then raster scanned into a single element detector at a 5 Hz rate. Dual modulation of pump and probe beams at disparate frequencies permits simultaneous measurement of both the bare reflectanceRand its photoinduced change ΔRthrough lock-in detection, allowing for continuously self-normalized measurement of ΔR/R. Example data are presented on a germanium wafer sample that demonstrate for signals of order ΔR/R ∼ 10−3, a 2.87 nm spectral resolution and fs temporal resolution pre-recompression, and comparable sensitivity to standard time-resolved, amplifier-based pump–probe techniques.more » « less
