![]() ![]() We compensated for dispersion by optimizing the second-harmonic generation (SHG) signal FWHM at the sample position using the MIIPS. The bandwidth was limited by the grating in the MIIPS system. 2) is then shaped and compressed using the Multiphoton Intrapulse Interference Phase Scan (MIIPS Biophotonic Solutions, Inc.) method. Using a dichroic mirror, light redder than 700 nm is attenuated and the portion spanning 525 to 700 nm (shown in Fig. By focusing the approximately 800 µJ pulse into a 2 m tube filled with 2 atm of argon gas, ultra-broadband pulses spanning from 450 to 900 nm were generated. The 800 nm output of a Coherent Micra Ti:sapphire oscillator was amplified in a Coherent Legend Elite regenerative amplifier to produce a 5 kHz, 4 W, 38 fs FWHM pulse train centered at 800 nm with approximately 35 nm of spectral bandwidth. The experimental apparatus is shown in Fig. The use of supercontinuum light sources in 2DES is now allowing access to broader spectral regions and even ultraviolet 2DES. As a result, we have designed a simple system to control the time delay with high resolution, while using all-reflective optics. In this work, we seek fine temporal resolution across a wide bandwidth without changes in temporal dispersion therefore, we avoid transmissive optics. Finally, the Soleil–Babinet compensator has recently been used for generating a time delay between two pulses. Moreover, delays can be set using spatial light modulators or acousto-optic modulators. The delay between pulses 1 and 2 can also be encoded along a spatial dimension, where multiple time delays are directly imaged on a camera in a single experiment. ![]() Delays can also be implemented with more precise control (<50 fs/mm) using paired, angled glass wedges, effectively “gearing” the delay. The accuracy can be further improved by using active phase stabilization. Timings can be controlled using retroreflectors mounted on sinusoidal encoded or piezoelectric motor stages that move parallel to the direction of beam propagation with control of approximately 6673 fs/mm. Several methods have been used to implement the requisite interferometric time delays in 2DES. Generation of phased 2DES spectra requires optical phase stability between the first two interactions and minimal temporal dispersion among the pulses. Interchange between pulses 1 and 2 allows collection of rephasing and nonrephasing spectra, which, taken together, can be phased to generate absorptive or dispersive 2D spectra. We then heterodyne the signal emitted in the phase-matched direction (− k 1 + k 2 + k 3) with an attenuated local oscillator (LO) pulse and collect data in the frequency domain using a CCD spectrometer. After the second interaction, the system undergoes evolution in the excited- or ground-state manifolds for a waiting time T, then a third pulse puts the system into a second optical coherence. The first and second pulses interact with a time separation τ (coherence time), during which the system evolves in an optical coherence between the ground and excited states. Briefly, a sequence of three ultrafast laser pulses interacts with the sample with precisely controlled time delays. The details of 2DES have been discussed extensively. Here, we investigate the multiple excited states in highly distinct chemical systems with important excitonic dynamics, CdSe quantum dots (QDs), and Chlorophyll a (Chl a). This method allows us to probe materials with ground-state and transient spectral features spanning several hundred nanometers, while limiting nonlinear dispersion. We exploit a simple method of obtaining precision time delays using reflective optics and angled translational stages. In this work, we describe an all-reflective implementation of 2DES with a single broadband continuum laser source for all interactions, which allows simultaneous interrogation of multiple electronic excited states. 2DES accesses detailed dynamical information without the use of multiple spectrally distinct laser pulses. Thus, 2DES can exploit spectrally broad, sub-10-fs, ultrafast pulses for pump and probe, while monitoring electronic and vibrational couplings and coherences across diverse chromophores and environments. This approach decouples the pulse bandwidth from the frequency resolution of the experiment, which is ultimately determined by the molecular response. The resulting 2D maps correlate excitation at a specific energy with the fate of that excitation across the entire excitation window. 2DES improves resolution compared to pump–probe spectroscopies by separating homogenous and inhomogeneous broadening along distinct spectral axes. It has been applied to study systems including spectral diffusion, photosynthetic light-harvesting, semiconducting nanocrystals and atomic vapors. Two-dimensional electronic spectroscopy (2DES) probes photo-initiated electronic dynamics on ultrafast timescales. ![]()
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