Within Atmosphere
When a Laser Gets in Its Own Way
A powerful laser can heat the air in its own path, creating a shifting lens that spreads the beam before it reaches the target.
On this page
- How absorbed laser energy heats and bends the air
- Why head on targets can make blooming worse
- How wind, power and beam diameter change the problem
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Introduction
Thermal blooming is one of the most counterintuitive limits on high-energy laser weapons: the beam can degrade its own path. As a powerful laser travels through the atmosphere, a small fraction of its energy is absorbed by air molecules, water vapour, aerosols and other particles. That absorbed energy heats the air along the beam route. The heated air becomes less dense, changing its refractive index and creating a weak optical lens that can spread, distort or steer the beam. Instead of remaining tightly focused on the target, the laser begins to defocus itself. This phenomenon, known as thermal blooming or self-defocusing, can reduce the energy delivered to a target even when the atmosphere appears relatively clear. Studies of high-energy laser propagation consistently identify thermal blooming as one of the dominant atmospheric limitations because it is generated by the beam itself rather than by external weather conditions alone. [NASA Technical Reports Server+2Optica]ntrs.nasa.govHere, a 'thermal lens' is…Read more…
How Absorbed Laser Energy Heats and Bends the Air
The atmosphere is never perfectly transparent. Even within favourable transmission windows, a small fraction of laser energy is absorbed during propagation. At ordinary power levels this effect is negligible. At weapon-class power levels, however, even modest absorption can deposit substantial heat into the air column crossed by the beam. [RP Photonics+2MDPI]rp-photonics.comthermal bloomingRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow…
As the air warms, it expands and becomes less dense. Air density directly influences refractive index, which determines how light travels through the medium. The centre of the beam path becomes a region of lower refractive index than the surrounding air. This density gradient acts like a negative lens that causes the beam to diverge rather than remain tightly concentrated. Researchers often describe the process as the creation of a thermally induced atmospheric lens. [NASA Technical Reports Server+2PathFinder]ntrs.nasa.govHere, a 'thermal lens' is…Read more…
The effect differs from ordinary diffraction. Every laser beam naturally spreads with distance because of diffraction. Thermal blooming adds an additional spreading mechanism driven by heat. The result can be a larger spot size on the target and a corresponding reduction in irradiance, the power delivered per unit area. Since laser weapons depend on concentrating energy onto a small point for a sufficient dwell time, even moderate beam expansion can significantly increase engagement times. [SPIE+2ADS (Astrophysics Data System)]spie.orgThe role of refractive index and velocity turbulence has been…Read more…
A useful way to think about thermal blooming is that the beam is attempting to shoot through a lens that it is continuously creating and reshaping for itself. The more power deposited into the atmosphere, the stronger that lens can become. [Optica+2Optica]opg.optica.orgThe importance of thermal blooming for laser weapon…by JF Daigle · 2021 · Cited by 1 — Thermal blooming occurs when a laser is s…
Why Head-On Targets Can Make Blooming Worse
Thermal blooming is not simply a function of laser power. Geometry matters. [galacticlibrary.net]galacticlibrary.netThermal Blooming - Galactic LibraryMar 7, 2026 — A high powered laser going through the air will cause the air to heat up due to absorption…
A laser engaging a target moving directly towards the weapon can experience particularly challenging blooming conditions because the beam repeatedly traverses nearly the same volume of atmosphere. The heated channel has less opportunity to move away from the optical path before additional energy is deposited into it. The laser therefore continues to propagate through air that it has already warmed. [RAND Corporation+2ADS (Astrophysics Data System)]rand.orgRAND CorporationMethod for Estimating the Thermal Blooming EffectIn the present study, a simple method has been developed to estimate the…
This feedback effect can become significant during engagements requiring long dwell times. If the beam must remain on target for several seconds, the heated air column can continue to evolve while the engagement is underway. The resulting refractive-index gradients may progressively reduce beam quality and target irradiance. Researchers studying laser weapon propagation have noted that thermal blooming becomes increasingly important when modelling sustained high-power engagements rather than short laboratory pulses. [Optica+2Optica]optica.orgOpen source on optica.org.
The problem is especially relevant at low altitudes, where atmospheric density is highest and where humidity, aerosols and maritime conditions can increase absorption. In naval scenarios, the beam may travel through humid marine boundary layers containing salt particles and water vapour, both of which contribute to energy deposition in the atmosphere and strengthen blooming effects. [deps.org+2Naval Postgraduate School]deps.orgOptimum Wavelength and Power for Efficient Laser…by P Sprangle · 2006 · Cited by 80 — Hcated aerosols conductively heat the surroundin…
This does not mean a laser cannot engage an approaching threat. Rather, it means that the effective range against a real target may be constrained not only by available power but also by the beam’s ability to maintain focus while traversing its own heated path.
How Wind Changes the Problem
Wind is often viewed as an obstacle for precision systems, but in the case of thermal blooming it can be beneficial.
Air movement carries heated air away from the beam path and replaces it with cooler air. This reduces the strength of the thermally induced lens and limits the accumulation of refractive distortions. Multiple modelling and experimental studies have found that increasing wind speed can lessen thermal blooming and improve beam focusing performance. [Optica]opg.optica.orgHigh-precision calculation and experiments on the thermal…by Q Zhang · 2023 · Cited by 15 — It showed that wind speed could redu…
The relationship is not perfectly simple. Strong winds can introduce other optical distortions through turbulence. Nevertheless, from a thermal blooming perspective, moving air generally helps because it prevents heat from remaining concentrated in the beam channel for long periods. [Optica+2afit.edu]opg.optica.orgHigh-precision calculation and experiments on the thermal…by Q Zhang · 2023 · Cited by 15 — It showed that wind speed could redu…
This creates an interesting operational reality: two engagements conducted under apparently similar weather conditions can produce different laser performance if local airflow differs significantly. A modest crosswind may improve propagation compared with stagnant air even though both situations appear equally clear to a human observer.
Why Power Can Become Part of the Limitation
A natural assumption is that increasing laser power should always improve weapon effectiveness. Thermal blooming complicates that assumption.
Higher power means more energy reaches the target, but it also means more energy is available to heat the atmosphere. Beyond certain conditions, increasing power can strengthen the self-defocusing effect enough that gains in delivered energy become smaller than expected. Historical and modern studies of high-energy laser propagation have repeatedly identified thermal blooming as a factor that can constrain how effectively additional power translates into target irradiance. [SPIE+2ADS (Astrophysics Data System)]spie.orgThe role of refractive index and velocity turbulence has been…Read more…
This does not create a hard universal ceiling because the outcome depends on wavelength, atmospheric absorption, range, beam diameter, turbulence and environmental conditions. However, it means that laser designers cannot simply pursue ever-greater output power without simultaneously addressing propagation physics. [Optica+2deps.org]opg.optica.orgHigh-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 285 — Physical processes affecting propagation in…
The challenge becomes particularly important for long-range engagements, where the beam has more distance over which to deposit heat into the atmosphere before reaching the target. A laser that performs well over a short test range may encounter substantially stronger blooming effects over operational distances. [AFIT Scholar+2Optica]scholar.afit.eduAFIT ScholarAtmospheric Propagation of High Energy Lasers: Thermal…Thermal blooming is a well documented phenomenon [15], whose releva…
Why Beam Diameter Matters
Beam diameter strongly influences how much heat is deposited into a given volume of air.
A narrow beam concentrates energy into a smaller cross-sectional area, producing higher local intensity and potentially stronger thermal gradients. A larger beam spreads the same power across a wider area, reducing local heating and weakening the thermal lensing effect. This is one reason why aperture size and beam-control strategies are important parts of directed-energy system design. [SPIE+2afit.edu]spie.orgThe role of refractive index and velocity turbulence has been…Read more…
The trade-off is that a larger beam generally requires larger optics and more demanding tracking and focusing systems. Designers therefore balance several competing requirements:
- High intensity on the target.
- Minimal atmospheric heating. [eureka.patsnap.com]eureka.patsnap.comreport atmospheric effects on long range laser power transmissionEffects On Long-Range Laser Power…Aug 28, 2025 — Thermal blooming mitigation techniques: Thermal blooming occurs when the atmosphere a…
- Practical optical system size.
- Acceptable beam quality over operational ranges.
The optimum solution depends on the intended mission. A system intended to defeat nearby drones may accept different compromises than a system intended for longer-range missile defence. [deps.org+2Optica]deps.orgOptimum Wavelength and Power for Efficient Laser…by P Sprangle · 2006 · Cited by 80 — Hcated aerosols conductively heat the surroundin…
How Modern Systems Try to Fight Blooming
Thermal blooming is not an unsolved problem, but neither is it something engineers can completely eliminate.
Modern directed-energy research employs adaptive optics, wavefront sensing, beam-control algorithms and propagation modelling to compensate for atmospheric distortions. Adaptive optics can partially correct beam distortions in real time, improving the concentration of energy on the target despite changing atmospheric conditions. Researchers continue to study how blooming interacts with turbulence, beam combining and different beam shapes in order to improve propagation efficiency. [AIAA Journal+2archive.ll.mit.edu]arc.aiaa.orgAIAA JournalAdaptive Optics for Directed Energy: Fundamentals and…Adaptive optics are beneficial for directed-energy applications when…
Accurate modelling has become increasingly important because thermal blooming is highly dynamic. The atmosphere changes as the beam changes it. Recent laser-weapon propagation studies emphasise that realistic performance predictions require thermal blooming to be included rather than treated as a minor correction. [Optica+2Optica]optica.orgOpen source on optica.org.
For directed-energy weapons, thermal blooming therefore represents a distinctive atmospheric limit: unlike fog, rain or dust, the beam is partly responsible for creating the obstacle. The more intensely the laser interacts with the atmosphere, the more important it becomes to manage the self-generated lens that can cause the weapon to get in its own way. [Optica+2RP Photonics]opg.optica.orgThe importance of thermal blooming for laser weapon…by JF Daigle · 2021 · Cited by 1 — Thermal blooming occurs when a laser is s…
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Endnotes
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Source: ntrs.nasa.gov
Link: https://ntrs.nasa.gov/api/citations/20120012963/downloads/20120012963.pdfSource snippet
Here, a 'thermal lens' is...Read more...
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Source: opg.optica.org
Link: https://opg.optica.org/abstract.cfm?uri=pcAOP-2021-PTh2E.4Source snippet
The importance of thermal blooming for laser weapon...by JF Daigle · 2021 · Cited by 1 — Thermal blooming occurs when a laser is s...
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Source: opg.optica.org
Link: https://opg.optica.org/ViewMedia.cfm?seq=0&uri=pcAOP-2021-PTh2E.4Source snippet
Energy Lasers (HEL) beam propagation in the atmosphere [2,3]. It stems from transverse...Read more...
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Source: rp-photonics.com
Title: thermal blooming
Link: https://www.rp-photonics.com/thermal_blooming.htmlSource snippet
RP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow...
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Source: mdpi.com
Link: https://www.mdpi.com/2304-6732/10/12/1343Source snippet
Thermal Blooming Effect of Power-Exponent-Phase Vortex...by F Zhang · 2023 · Cited by 8 — When a high-power laser beam propagates th...
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Source: spie.org
Link: https://spie.org/Publications/Proceedings/Volume/1221Source snippet
The role of refractive index and velocity turbulence has been...Read more...
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Source: rand.org
Link: https://www.rand.org/content/dam/rand/pubs/reports/2007/R1726.pdfSource snippet
RAND CorporationMethod for Estimating the Thermal Blooming EffectIn the present study, a simple method has been developed to estimate the...
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Source: deps.org
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Optimum Wavelength and Power for Efficient Laser...by P Sprangle · 2006 · Cited by 80 — Hcated aerosols conductively heat the surroundin...
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Source: opg.optica.org
Link: https://opg.optica.org/abstract.cfm?uri=ao-54-31-f201Source snippet
High-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 287 — Specifically, we discuss the effects of abs...
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Source: opg.optica.org
Link: https://opg.optica.org/abstract.cfm?uri=oe-31-16-25900Source snippet
High-precision calculation and experiments on the thermal...by Q Zhang · 2023 · Cited by 15 — It showed that wind speed could redu...
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Link: https://www.afit.edu/BIOS/publications/Lane_Akers_Reeger_Cook_Richardson.pdf -
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Link: https://arc.aiaa.org/doi/10.2514/1.J061766Source snippet
AIAA JournalAdaptive Optics for Directed Energy: Fundamentals and...Adaptive optics are beneficial for directed-energy applications when...
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Source: opg.optica.org
Link: https://opg.optica.org/ao/abstract.cfm?uri=ao-54-31-f201Source snippet
High-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 285 — Physical processes affecting propagation in...
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AFIT ScholarAtmospheric Propagation of High Energy Lasers: Thermal...Thermal blooming is a well documented phenomenon [15], whose releva...
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Source: archive.ll.mit.edu
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Thermal-Blooming Laboratory ExperimentsWe conducted a multiphase series of laboratory experiments to explore the adaptive optics compensa...
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Atmospheric Propagation of High Energy Lasers: Thermal...by J Gustafssona — High Energy Laser propagation through turbulent atmosphere i...
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Car Alarms | Remote Starters | SMARTSTART...DIRECTED is the largest designer and marketer of consumer-branded car alarms and...
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blooming of repetitively pulsed laser beamsby J Wallace · 1974 · Cited by 45 — In this paper, we have theoretically evaluated the propaga...
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Source: opg.optica.org
Title: upcoming pdf.cfm
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blooming effect of Hermite–Gaussian beams...by Z Ding · 2019 · Cited by 30 — The thermal blooming effect of Hermite–Gaussian (H-G) beams...
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Based on the analytical expression of thermal...Read...
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Title: Path Finder Self-Defocusing/Thermal Bloom
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Self-Defocusing/Thermal Bloom - Pathfinder Digital3 Sept 2025 — Self-defocusing in free-space optics (FSO) describes the divergence of a...
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This paper presents a tutorial review of the self-induced thermal distortion of laser radiation propagating in absorbing media.Read more...
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Naval Postgraduate SchoolPropagation of High Energy Lasers for Various...HEL performance is strongly affected by various atmospheric eff...
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Thermal Blooming - Galactic LibraryMar 7, 2026 — A high powered laser going through the air will cause the air to heat up due to absorption...
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Source: Wikipedia
Title: Thermal blooming
Link: https://en.wikipedia.org/wiki/Thermal_bloomingSource snippet
Thermal bloomingThermal blooming or thermal lensing occurs when high-energy laser beams propagate through a medium. It is the result o...
Additional References
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Source: defencesciencereview.com.pl
Link: https://www.defencesciencereview.com.pl/Laser-Based-Directed-Energy-Weapons-Technological-Capabilities-Material-Interaction%2C216776%2C0%2C2.htmlSource snippet
Laser-Based Directed Energy Weapons: Technological...by A Karkadakattil · 2026 · Cited by 1 — Objectives: This review aims to evaluate t...
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Source: researchgate.net
Link: https://www.researchgate.net/publication/26721062_Laser_Beam_Self-Focusing_in_the_AtmosphereSource snippet
Laser Beam Self-Focusing in the AtmosphereWe propose to exploit a self-focusing effect in the atmosphere to assist delivering powerful la...
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Link: https://publications.sto.nato.int/publications/STO%20Educational%20Notes/STO-EN-SCI-340/EN-SCI-340-06.pdfSource snippet
nato.int6.0 PROPAGATION AND ADAPTIVE OPTICSThe primary initial effects of thermal blooming are to bend the laser beam toward the cooler...
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Source: researchgate.net
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Thermal blooming is manifest as strong distortions of laser beams that were first. detected in beam propagation...Read more...
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Link: https://pure.psu.edu/en/publications/effect-of-steady-state-thermal-blooming-on-atmospheric-propagatio/Source snippet
of steady-state thermal blooming on atmospheric...by M Kumar · 2025 · Cited by 1 — In this article, the effect of steady-state thermal b...
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Source: eureka.patsnap.com
Title: report atmospheric effects on long range laser power transmission
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Effects On Long-Range Laser Power...Aug 28, 2025 — Thermal blooming mitigation techniques: Thermal blooming occurs when the atmosphere a...
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Source: researchgate.net
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mitigated through feedback from wavefront and atmospheric sensors to the adaptive...Read more...
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Source: researchgate.net
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ive effects such as scattering, turbulence and thermal blooming...
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Source: researchgate.net
Link: https://www.researchgate.net/publication/307438686_Directed_Energy_WeaponsSource snippet
cts when propagation media temperature increases varying...
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Source: youtube.com
Title: Test footage of UK Dragon Fire Laser Directed Energy Weapon
Link: https://www.youtube.com/watch?v=XCK9ghnv-VASource snippet
We Could Build the Hammer of Dawn - Except For One Thing - YouTube We Could Build the Hammer of Dawn - Except For One Thing - YouTube...
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