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Time-domain thermoreflectance

Nature Reviews Methods Primers volume 5, Article number: 55 (2025) Cite this article

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Abstract

Time-domain thermoreflectance (TDTR) has been instrumental in measuring the heat transfer properties of bulk and nanostructured materials over the past two decades. In this Primer, we describe the optical and thermal aspects of TDTR, with an in-depth discussion on the theory, apparatus design and implementation. We present examples that illustrate the ability of TDTR to measure thermal conductivity tensors, thermal conductance across material interfaces, and volumetric heat capacity of thin films, 2D materials and bulk materials. The ability of TDTR to spatially resolve thermal properties is useful for studying heterogeneous material systems, such as materials processed in or subjected to extreme environments. We consider current limitations of pump–probe metrologies and discuss recent advancements of TDTR, such as time-resolved magneto-optic Kerr effect (TR-MOKE), beam-offset TDTR/TR-MOKE, steady-state thermoreflectance, frequency-domain thermoreflectance and laser-flash TDTR. Finally, we present an outlook on anticipated technological developments to further expand the ability of TDTR to measure nanoscale thermal properties.

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Fig. 1: Introduction to optical pump–probe metrologies for thermal property measurements.
Fig. 2: Optical schematic for time-domain thermoreflectance and experimental variants.
Fig. 3: Thermal responses to different types of heating.
Fig. 4: Representative data for common time-domain thermoreflectance experiments.
Fig. 5: Representative data for time-resolved magneto-optic Kerr effect and laser-flash time-domain thermoreflectance.
Fig. 6: Diverse applications of time-domain thermoreflectance for thermal characterization.

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Acknowledgements

Work by R.M. and P.E.H. was supported as part of the 3D Ferroelectric Microelectronics Manufacturing (3DFeM2), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences Energy Frontier Research Centers programme under award number DE-SC0021118. Work by S.K. and R.B.W. was supported as part of ULTRA, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under award number DE-SC0021230.

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Author notes

  1. These authors contributed equally: Ramya Mohan, Samreen Khan.

Authors and Affiliations

  1. Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, USA

    Ramya Mohan & Patrick E. Hopkins

  2. Department of Mechanical Engineering, University of California, Riverside, CA, USA

    Samreen Khan & Richard B. Wilson

  3. Materials Science and Engineering Program, University of California, Riverside, CA, USA

    Richard B. Wilson

  4. Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, USA

    Patrick E. Hopkins

  5. Department of Physics, University of Virginia, Charlottesville, VA, USA

    Patrick E. Hopkins

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Corresponding authors

Correspondence to Richard B. Wilson or Patrick E. Hopkins.

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Competing interests

P.E.H. is co-founder of Laser Thermal Analysis, Inc., a company that has commercialized frequency-domain thermoreflectance (FDTR) and steady-state thermoreflectance (SSTR) instruments. The other authors declare no competing interests.

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Supplementary information

Glossary

Coherent pickup

Unintended leakage of the reference signal at the pump modulation frequency (\({f}_{\mathrm{mod}}\)) into the measurement input of the lock-in through radiative, capacitive or conduction paths. As it occurs at the reference frequency, it cannot be filtered out by the lock-in, despite not originating from the sample.

Mean free paths

The average distances that particles or quasi-particles (carriers such as electrons, phonons or magnons) travel between scattering events that alter their momentum or energy.

Multilayer thermal model

A framework for predicting the thermal response of the sample to heating. Thermal transport in each layer is assumed to be governed by a layer-specific heat equation, and transport between layers is governed by boundary conditions that assume the heat current is continuous across the boundary and that temperature drops at the interface are governed by the interface conductance between the two layers.

Phonon focusing

The propagation of phonons preferentially along certain crystallographic orientations in anisotropic materials.

Picosecond acoustics

Non-thermal signals in pump–probe measurements that arise from strain-induced changes to the reflectivity. The initial temperature gradient in the metal transducer after absorption of the pump pulse generates a strain wave that propagates into the sample, reflects from buried interfaces and eventually returns to the metal film surface. The time delay of the acoustic waves’ echoes is determined by the film thickness and the longitudinal speed of sound.

Pulse accumulation

Temperature response of the sample caused by the accumulated response from the pump pulses that heated the sample prior to zero time delay. Pulse accumulation occurs when energy from a previous pulse is not conducted away before the arrival of the subsequent pump pulse.

Thermal model

The iterative Feldman algorithm used to analyse heat conduction in layered structures.

Thermal transport phenomena

The processes involved in the transfer of energy (heat) through various media, including solids, liquids and gases.

Thermoreflectance

Change of reflectance with temperature.

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Mohan, R., Khan, S., Wilson, R.B. et al. Time-domain thermoreflectance. Nat Rev Methods Primers 5, 55 (2025). https://doi.org/10.1038/s43586-025-00425-8

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