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A major limitation of transient optical spectroscopy is that relatively high laser fluences are required to enable broadband, multichannel detection with acceptable signal-to-noise levels. Under typical experimental conditions, many condensed phase and nanoscale materials exhibit fluence-dependent dynamics, including higher order effects such as carrier–carrier annihilation. With the proliferation of commercial laser systems, offering both high repetition rates and high pulse energies, have come new opportunities for high sensitivity pump-probe measurements at low pump fluences. However, experimental considerations needed to fully leverage the statistical advantage of these laser systems have not been fully described. Here, we demonstrate a high repetition rate, broadband transient spectrometer capable of multichannel shot-to-shot detection at 90 kHz. Importantly, we find that several high-speed cameras exhibit a time-domain fixed pattern noise resulting from interleaved analog-to-digital converters, which is particularly detrimental to the conventional “ON/OFF” modulation scheme used in pump-probe spectroscopy. Using a modified modulation and data processing scheme, we achieve a noise level of 10−5 in 4 s for differential transmission, an order of magnitude lower than for commercial 1 kHz transient spectrometers for the same acquisition time. We leverage the high sensitivity of this system to measure the differential transmission of monolayer graphene at low pump fluence. We show that signals on the order of 10−6 OD can be measured, enabling a new data acquisition regime for low-dimensional materials.
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This content will become publicly available on November 6, 2026
Optimizing Detection Schemes for Broadband Pump‐Probe Microscopy
Although similar to more commonly implemented single wavelength approaches, broadband pump‐probe or transient absorption microscopy presents unique experimental challenges due to the simultaneous requirements of a broadband probe pulse and a small sample volume. Here we provide an in‐depth analysis of broadband detection schemes and their common noise sources to provide strategies for balancing the conflicting needs of high sensitivity and low probe fluence. We show that broadband pump‐probe microscopy is atypically sensitive to laser shot noise and therefore, low pump on/off modulation frequencies, on the order of 100 s of Hz to a few kHz, are essential to measure small (~10^-3 - 10^-4) amplitude transient spectra while remaining in the perturbative limit.
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- Award ID(s):
- 2154448
- PAR ID:
- 10646225
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Microscopy Research and Technique
- ISSN:
- 1059-910X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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