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  • Primer
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Transient absorption spectroscopy

Nature Reviews Methods Primers volume 6, Article number: 34 (2026) Cite this article

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Abstract

Transient absorption (TA) spectroscopy has become a widely used method for tracking photoinduced dynamics in molecules, materials, devices and biological systems. By measuring pump-induced absorption changes, TA provides direct access to excited-state populations, energy-transfer and charge-transfer processes and transient intermediates with femtosecond temporal resolution and broad spectral coverage. This Primer examines how TA spectroscopy can be used to interrogate non-equilibrium processes, introducing the physical origin of TA signals and the most common experimental implementations, with emphasis on instrumentation, measurement strategies and data analysis. We discuss practical considerations, including spectral–temporal calibration, chirp correction, global and target analysis, noise suppression and reproducibility, and highlight representative applications across chemistry, physics and materials science. Finally, we address current limitations of TA spectroscopy and outline emerging directions, including multimodal and multidimensional implementations, machine-learning-assisted analysis and integration with complementary ultrafast spectroscopies.

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Fig. 1: Schematic of transient absorption spectroscopy.
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Fig. 2: Illustration of a transient absorption set-up.
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Fig. 3: Illustration of transient absorption data processing.
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Fig. 4: Example of transient absorption data analysis on interfacial charge-transfer process.
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Fig. 5: Representative examples showing the application of transient absorption spectroscopy.
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Acknowledgements

H.Z. thanks the financial support from the National Natural Science Foundation of China (92477125 and 22273084) and Fundamental Research Funds for the Zhejiang Provincial Universities (226-2025-00260). This study is supported by the open fund of the State Key Laboratory of Molecular Reaction Dynamics in DICP, CAS and Instrument Innovation Program of Institute of Fundamental and Transdisciplinary Research, Zhejiang University. T.L. thanks the financial support from US Department of Energy, Office of Basic Energy Sciences, Solar Photochemistry Program under award number DE-SC0026199.

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Author notes

  1. These authors contributed equally: Sheng He, Peipei Jin.

Authors and Affiliations

  1. Department of Chemistry, Emory University, Atlanta, GA, USA

    Sheng He & Tianquan Lian

  2. Zhejiang Key Laboratory of Excited-State Energy Conversion and Energy Storage, Department of Chemistry, Institute of Fundamental and Transdisciplinary Research, Zhejiang University, Hangzhou, China

    Peipei Jin & Haiming Zhu

  3. Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA

    Tianquan Lian

Authors
  1. Sheng He
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  2. Peipei Jin
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  3. Tianquan Lian
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  4. Haiming Zhu
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Contributions

Introduction (S.H. and H.Z.); Experimentation (S.H. and H.Z.); Results (S.H. and H.Z.); Applications (P.J. and H.Z.); Reproducibility and data deposition (S.H. and H.Z.); Limitations and optimizations (P.J. and H.Z.); Outlook (P.J. and H.Z.); overview of the Primer (T.L. and H.Z.).

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Correspondence to Haiming Zhu.

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Nature Reviews Methods Primers thanks Jianzhang Zhao, Zach Walbrun and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Glossary

ABC recombination model

A standard phenomenological framework that quantifies the total free carrier recombination rate in semiconductors as the sum of three carrier-density-dependent terms: first-order Shockley–Read–Hall trap-assisted non-radiative recombination (denoted as coefficient A), second-order bimolecular radiative recombination (coefficient B) and third-order Auger non-radiative recombination (coefficient C).

Asynchronous optical sampling

A pump–probe acquisition scheme that uses two laser systems with slightly detuned repetition rates. The constant repetition rate difference causes the time delay between the pump and probe pulse pairs to increment automatically with each laser shot, scanning through the full interpulse period.

Chirp correction

A computational post-processing step applied to raw transient absorption data to remove the temporal distortion caused by group velocity dispersion, which causes different probe wavelengths to arrive at the sample at different times, thereby restoring a physically accurate time zero across the entire spectrum.

Dark noise

Stochastic electronic noise present in a photodetector when no optical signal is incident, arising primarily from thermally generated charge carriers.

Excited-state absorption

(ESA). Induced absorption from a populated excited state to a higher-lying state, resulting in a positive change in absorbance.

Ground-state bleach

(GSB). These signals correspond to a decrease in absorption at the probe wavelength owing to the depletion of molecules or materials in the ground state following the photoexcitation by the pump pulse.

High-harmonic generation

A highly nonlinear optical process in which intense, ultrashort laser pulses drive the emission of coherent light at odd-integer multiples of the fundamental frequency of driving laser, often extending into the extreme ultraviolet and soft X-ray spectral regions.

Knife edge scanning method

A beam profiling technique in which a sharp, opaque edge is translated through a focused laser beam while the transmitted power is recorded; the resulting sigmoidal transmission curve is differentiated to obtain the beam’s spatial intensity profile and calculate its waist.

Mechanical chopper

A synchronized, rotating wheel with a patterned aperture (for example, a slit) that periodically blocks the pump beam at a set frequency.

Rapid-scan

A motorized delay stage continuously and repetitively sweeps the pump–probe time delay while the probe signal is recorded in real time, building up a complete transient trace over many successive scans.

Readout noise

The electronic noise introduced during the process of converting the stored charge in a detector’s pixels into a measurable voltage signal, which adds a fixed uncertainty to each pixel value and is independent of both the signal level and integration time.

Shot noise

The fundamental, signal-dependent statistical noise arising from the discrete quantum nature of light and charge, whose magnitude scales as the square root of the total number of photoelectrons and sets the theoretical signal-to-noise limit for an ideal detector.

Step-scan

The pump–probe delay is incremented in discrete, preset steps, and at each delay position the probe signal is fully acquired, typically by averaging over many pump modulation cycles, before the delay stage moves to the next temporal point.

Supercontinuum generation

A nonlinear process in which an intense, narrowband pump pulse propagates through a medium, resulting in a dramatic spectral broadening that produces a coherent, broadband white-light continuum.

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He, S., Jin, P., Lian, T. et al. Transient absorption spectroscopy. Nat Rev Methods Primers 6, 34 (2026). https://doi.org/10.1038/s43586-026-00488-1

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