About
Jyotirmoy Mandal is an Assistant Professor of Civil and Environmental Engineering at Princeton University. He holds a PhD in Applied Physics from Columbia University and a BA in Physics and Mathematics from Vanderbilt University. His research focuses on understanding and controlling nano-to-macro scale radiative heat flows in natural environments and artificial surfaces, with an emphasis on characterizing and mitigating ambient heat in a warming world. His work lies at the intersection of optics and materials science, involving the creation of photonic and plasmonic metamaterials with novel optical properties. Additionally, he designs scalable materials that radiatively thermoregulate to promote sustainable and climate-resilient human environments. His research interests also include optical component design for infrared heat detection, water harvesting using passive cooling technologies, modeling large-scale impacts of radiative cooling for geoengineering, and exploring optical and radiative phenomena in the natural world. Dr. Mandal has received notable honors such as the Schmidt Science Fellowship and the Simons Prize for the most outstanding dissertation at Columbia University.
Research topics
- Computer Science
- Physics
- Optics
- Materials science
- Nanotechnology
- Thermodynamics
- Composite material
- Optoelectronics
- Chemistry
- Architectural engineering
- Engineering physics
- Engineering
- Meteorology
- Civil engineering
- Environmental science
Selected publications
arXiv (Cornell University) · 2026-03-03
articleOpen accessSenior authorA surface that selectively emits heat in the long-wave infrared (LWIR) can enable passive cooling in hot environments while retaining partial radiative insulation in cold conditions, but its real-world deployment is limited by reliance on ultrabroadband metallic reflectors such as silver. Here we engineer random photonic media with a layered, multiscale scattering architecture to simultaneously achieve ultraviolet-to-far-infrared reflection and selective LWIR emission. We validate our approach by developing a metal-free selective emitter that exhibits high LWIR emittance (0.88), strong solar reflectance (0.97), and low thermal emittance outside the LWIR (0.49), independent of the substrate. Field tests, supported by theoretical modeling, show enhanced radiative cooling and thermoregulation across diverse applications relative to conventional broadband emitters. Leveraging the low cost and scalable manufacturing of scattering media, this work provides a pathway to advance radiative thermal management, enabling energy saving and improved thermal comfort.
arXiv (Cornell University) · 2026-03-03
preprintOpen accessSenior authorA surface that selectively emits heat in the long-wave infrared (LWIR) can enable passive cooling in hot environments while retaining partial radiative insulation in cold conditions, but its real-world deployment is limited by reliance on ultrabroadband metallic reflectors such as silver. Here we engineer random photonic media with a layered, multiscale scattering architecture to simultaneously achieve ultraviolet-to-far-infrared reflection and selective LWIR emission. We validate our approach by developing a metal-free selective emitter that exhibits high LWIR emittance (0.88), strong solar reflectance (0.97), and low thermal emittance outside the LWIR (0.49), independent of the substrate. Field tests, supported by theoretical modeling, show enhanced radiative cooling and thermoregulation across diverse applications relative to conventional broadband emitters. Leveraging the low cost and scalable manufacturing of scattering media, this work provides a pathway to advance radiative thermal management, enabling energy saving and improved thermal comfort.
How do sub-bandgap reflectors affect the performance of PV modules?
arXiv (Cornell University) · 2026-04-22
preprintOpen accessSub-bandgap reflectors (SBR) can reduce the temperature of photovoltaic (PV) modules by reflecting the near-infrared region of the solar spectrum with photon energies smaller than the electronic bandgap of the solar cell absorber material. We consider an ideal SBR, which reflects 100 % of non-harvestable low-energy photons but does not alter the reflectivity of the PV module for usable high-energy photons, and estimate how reducing the module temperature with the SBR affects the annual and the cumulative energy yield of silicon PV modules for six locations in North America and Europe. An ideal SBR would increase the annual energy yield between 1.0 % and 1.5 % for open-rack mounted modules and between 1.6 % and 2.4 % for close-roof mounted PV modules. Whether a non-ideal SBR provides a benefit in actual deployments strongly depends on the location and the optical properties of the coating. Beyond effects on the instantaneous power conversion efficiency and hence the annual energy yield, reducing the temperature by a SBR might also reduce the degradation and increase the overall lifetime of the PV module. By describing degradation using a simple Arrhenius approach using typical activation energies between 0.4 eV and 0.8 eV, we find that an ideal SBR increases the cumulative energy yield over 30 years between 2.2 % and 4.0 % for an open-rack mounted PV module in Princeton, New Jersey, USA.
How do sub-bandgap reflectors affect the performance of PV modules?
ArXiv.org · 2026-04-22
articleOpen accessSub-bandgap reflectors (SBR) can reduce the temperature of photovoltaic (PV) modules by reflecting the near-infrared region of the solar spectrum with photon energies smaller than the electronic bandgap of the solar cell absorber material. We consider an ideal SBR, which reflects 100 % of non-harvestable low-energy photons but does not alter the reflectivity of the PV module for usable high-energy photons, and estimate how reducing the module temperature with the SBR affects the annual and the cumulative energy yield of silicon PV modules for six locations in North America and Europe. An ideal SBR would increase the annual energy yield between 1.0 % and 1.5 % for open-rack mounted modules and between 1.6 % and 2.4 % for close-roof mounted PV modules. Whether a non-ideal SBR provides a benefit in actual deployments strongly depends on the location and the optical properties of the coating. Beyond effects on the instantaneous power conversion efficiency and hence the annual energy yield, reducing the temperature by a SBR might also reduce the degradation and increase the overall lifetime of the PV module. By describing degradation using a simple Arrhenius approach using typical activation energies between 0.4 eV and 0.8 eV, we find that an ideal SBR increases the cumulative energy yield over 30 years between 2.2 % and 4.0 % for an open-rack mounted PV module in Princeton, New Jersey, USA.
Compound urban extremes weaken the cooling efficacy of super cool broadband materials in cities
Urban Climate · 2026-01-05
articleOpen accessDelhi, one of the fastest-warming megacities globally, frequently experiences compound urban extremes. This study evaluates the radiative–dynamic performance of super cool broadband materials under compound urban extremes. During peak heat episodes, super cool broadband materials can reduce surface temperature by up to 6.3 °C, roof temperature to 34.8 °C, and ambient air temperature by 3.2 °C, with an urban-average cooling of 2.9 °C. Reduced net radiation limits sensible heat flux, weakens buoyant turbulence, and suppresses vertical momentum exchange, resulting in enhanced mesoscale stabilization following surface cooling. Additionally, convective fluxes decline, lowering wind speed by 3.2 m s −1 and planetary boundary-layer height by 752.6 m. Under high-humidity conditions (>75 %), elevated atmospheric water vapor narrows the radiative window and increases downward longwave flux, while enhanced latent heat flux reduces sensible heat release. Net radiation decreases by 276 W m −2 , surface temperature falls by 5.2 °C, roof temperature reaches 30.4 °C, and ambient air cools by 2.4 °C, accompanied by a 9.6 % rise in relative humidity and reductions in wind speed and boundary-layer height to 2.7 m s −1 and 677.1 m. During severe PM₂.₅ pollution (>100 μg m −3 ), aerosol scattering and absorption further reduce insolation, lowering net radiation by 265 W m −2 and causing 4.7 °C surface and 2.2 °C ambient cooling. The optical design of super cool broadband materials sustains reflectivity and emissivity under heat, humidity, and aerosol-laden skies, maintaining a net radiative deficit and converting urban surfaces from heat sources into radiative sinks, enabling robust, condition-sensitive cooling under Delhi’s combined extremes. • Aerosol–heat–humidity interactions alter urban surface radiative forcing and convection. • Super-cool broadband materials cooled surface 6.3 °C and ambient 3.2 °C under dry heat. • High humidity and aerosols curtailed infrared emission and solar reflection, reducing cooling. • Reduced surface cooling weakened turbulence and boundary-layer ventilation in cities. • Radiative–convective feedbacks govern cooling efficacy and climatic trade-offs of materials.
Advanced Materials · 2026-03-01
articlePopulus alba–Inspired Thermal Regulation In their Research Article (DOI: 10.1002/adma.202516537), Dae-Hyeong Kim, Young Min Song, and co-workers present a radiative-latent thermostat (LRT) inspired by Populus alba leaves. The LRT provides dynamic solar reflectance, high infrared emissivity, and reversible water sorption–desorption capabilities within a hydrogel system to achieve adaptive, passive thermal regulation across varying outdoor environments.
Optics for Terawatt-Scale Photovoltaics – Review and Perspectives
2025-04-01
preprintOpen accessPhotovoltaics—a mature technology—is set to play a vital role in achieving a carbon-free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question: How can optics facilitate the large-scale deployment of photovoltaics necessary for decarbonizing our societies?
Balancing radiative cooling with thermal mass and buoyancy ventilation
Journal of Physics Conference Series · 2025-11-01
articleOpen accessAbstract Global demand for space cooling is increasing due to climate change. In this study, the coupling of radiative cooling, thermal mass, and buoyancy ventilation is investigated as an alternative to mechanical air-conditioning. A scalable analytical model is calibrated from a reduced-scale experiment to investigate the effect of different thermal mass distributions between an uninsulated roof radiator and an enclosed space. It is found that a high-mass roof radiator is a viable option for summertime temperature and natural ventilation stability, but a light (or thin) roof radiator and more thermal mass indoors is a more efficient option. Maximum nighttime cooling can be achieved at the expense of temperature stability.
2025-09-18
articleSenior authorAdaptive radiative coolers, like thermochromic and electrochromic thermal emitters, are more energy-efficient than traditional radiative coolers because they do not overcool buildings in the winter. This means that they have a CO<sub>2</sub> emissions reductions benefit from a climate-change perspective. However, because this functionality also inevitably traps solar or longwave heat on earth, adaptive radiative coolers may not be sustainable for building thermoregulation. We show through first order calculations that compared to static traditional radiative coolers, adaptive radiative coolers with switchable emittance will trap more heat on earth than they will help lose by reducing CO<sub>2</sub> emissions, for the foreseeable future. Detailed calculations show that adaptive radiative coolers may have a net heating penalty relative to traditional radiative coolers that lasts beyond this century.
Optics for Terawatt-Scale Photovoltaics – Review and Perspectives
2025-03-08
preprintOpen accessPhotovoltaics—a mature technology—is set to play a vital role in achieving a carbon-free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question: How can optics facilitate the large-scale deployment of photovoltaics necessary for decarbonizing our societies?
Frequent coauthors
- 30 shared
Aaswath P. Raman
- 19 shared
Yuan Yang
- 18 shared
Nanfang Yu
- 8 shared
Sagar Mandal
Seattle University
- 7 shared
Meijie Chen
Ji Hua Laboratory
- 6 shared
Adam C. Overvig
City University of New York
- 5 shared
James H. Dickerson
Providence College
- 5 shared
Qian Cheng
Beijing Institute of Technology
Labs
Awards & honors
- Schmidt Science Fellow (2020)
- Simons Prize for the most outstanding dissertation, Columbia…
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