1,721,235 research outputs found
In situ femtosecond spectroelectrochemistry of Au(1 1 1) in an aqueous chloride solution
No full textTime-resolved methods in biophysics. 4. Broadband pump-probe spectroscopy system with sub-20 fs temporal resolution for the study of energy transfer processes in photosynthesis
No full textDeep reinforcement learning control of white-light continuum generation
Full text linkWhite-light continuum (WLC) generation in bulk media finds numerous applications in ultrafast optics and spectroscopy. Due to the complexity of the underlying spatiotemporal dynamics, WLC optimization typically follows empirical procedures. Deep reinforcement learning (RL) is a branch of machine learning dealing with the control of automated systems using deep neural networks. In this Letter, we demonstrate the capability of a deep RL agent to generate a long-term-stable WLC from a bulk medium without any previous knowledge of the system dynamics or functioning. This work demonstrates that RL can be exploited effectively to control complex nonlinear optical experiments
Two-color pump-probe system broadly tunable over the visible and the near infrared with sub-30 fs temporal resolution
No full textWe describe an ultrafast spectroscopy system based on two synchronized noncollinear optical parametric amplifiers (NOPAs). Each NOPA can be independently configured to generate ultrabroadband sub-10 fs visible pulses, tunable 15 fs visible pulses (500–720 nm), tunable 15–30 fs near-infrared pulses (900–1500 nm), and 15–20 fs blue pulses (430–480 nm). This system enables to perform pump-probe experiments over nearly two octaves of spectrum with unprecedented temporal resolution. We present application examples highlighting the capability of this instrument to track excited-state dynamics occurring on the sub-100 fs time scale: electron transfer in polymer-fullerene blends, intersubband energy relaxation in carbon nanotubes, and internal conversion in carotenoids
High-time-resolution pump-probe system with broadband detection for the study of time-domain vibrational dynamics
No full textWe present an ultrafast transient absorption spectroscopy system in the visible combining high-sensitivity broadband detection with extreme temporal resolution. The instrument is based on an ultrabroadband sub-10 fs optical parametric amplifier coupled to an optical multichannel analyzer with fast electronics, enabling single-shot detection at 1 kHz repetition rate. For a given pump-probe delay τ, we achieve a differential transmission (ΔT/T) sensitivity of the order of 10−4 over the λpr = 490–720 nm probe wavelength range by averaging over 1000 shots, allowing the acquisition of complete two-dimensional ΔT/T (λpr,τ) maps within a few minute measurement time. We present application examples highlighting the capability of this instrument to observe ultrafast dynamical processes, follow impulsively excited vibrational motions with frequency as high as 3000 cm−1 (11 fs period), and determine the probe wavelength dependence of amplitude and phase of the oscillations
Balanced detection SRS microscopy
No full textPulsed laser systems, especially those based on fiber technology, employed for SRS microscopy often present excess noise that prevents the user from reaching the shot-noise limit and increases the imaging time. This is detrimental, as SRS is often employed as an alternative to spontaneous Raman when imaging speed is an issue. To compensate for these fluctuations, one can use balanced detection. It employs a second photodiode to monitor the laser fluctuations by splitting a portion of the beam before the sample and subtracts this signal from the one generated at the photodiode after the sample. However, the sample often presents spatially varying transmission, thus unbalancing the two photodiodes. Several solutions to this problem have been proposed and demonstrated in the literature and reviewed in this chapter
Time-domain measurement of optical activity by an ultrastable common-path interferometer
Full text linkWe introduce a novel configuration for the broadband measurement of the optical activity of molecules, combining time-domain detection with heterodyne amplification. A birefringent common-path polarization-division interferometer creates two phase-locked replicas of the input light with orthogonal polarization. The more intense replica interacts with the sample, producing a chiral free-induction decay field, which interferes with the other replica, acting as a time-delayed phase-coherent local oscillator. By recording the delay-dependent interferogram, we obtain by a Fourier transform both the circular dichroism and circular birefringence spectra. Our compact, low-cost setup accepts ultrashort light pulses, making it suitable for measurement of transient optical activity
Observation of High-Frequency Coherent Vibrational Motion with Strongly Chirped Probe Pulses
No full textObservation of High-Frequency Coherent Vibrational Motion with Strongly Chirped Probe Pulse
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