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Why Self Heated Air Still Defeats Smart Mirrors

Thermal blooming is difficult because the laser creates part of the distortion itself, forcing correction systems to chase a moving problem.

On this page

  • How high power beams heat their own path
  • Why self made distortion is harder to predict
  • Where adaptive correction helps and where it falls short
Preview for Why Self Heated Air Still Defeats Smart Mirrors

Introduction

Thermal blooming remains one of the hardest propagation problems for high-energy laser systems because the laser beam creates part of the distortion that it is trying to overcome. Unlike ordinary atmospheric turbulence, which exists independently of the beam, thermal blooming is a self-induced effect: a fraction of the laser energy is absorbed by the air, heating it and changing its refractive index. The heated air then acts like a dynamic lens that defocuses, bends, or reshapes the beam. Adaptive optics can compensate for some of these distortions, but it is often forced to correct a problem that is continuously being generated by the beam itself. As laser power increases, this feedback loop becomes more severe, making thermal blooming a persistent limitation even in systems equipped with sophisticated wavefront-control technology. [RP Photonics+2Optica Publishing Group]rp-photonics.comthermal bloomingRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow…

Blooming Limits illustration 1

How High-Power Beams Heat Their Own Path

Thermal blooming begins when atmospheric molecules absorb a small fraction of a laser’s energy. The absorbed energy raises the local air temperature, reducing air density and altering the refractive index along the beam path. Even modest absorption can become significant when laser powers reach the levels associated with directed-energy applications. The result is a refractive structure in the atmosphere that behaves like a weak, continuously changing optical element. [RP Photonics+2Panoptes]rp-photonics.comthermal bloomingRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow…

The distortion is not simply a matter of the beam becoming blurry. Depending on wind conditions, propagation distance, wavelength, and power level, thermal blooming can produce:

  • Beam spreading that lowers energy density on target.
  • Beam steering or drift as the beam bends toward cooler air.
  • Asymmetric distortions that reshape the beam profile.
  • Time-varying aberrations that evolve during propagation. [Panoptes+2MDPI]panoptesv.comPanoptes Thermal BloomingPanoptesThermal Blooming - How to Build a Laser Death RayThe gradient in air density acts like a weak lens that acts to defocus the beam…

A key difference from ordinary turbulence is causality. Turbulence distorts the beam because the atmosphere is already irregular. Thermal blooming occurs because the beam modifies the atmosphere first and then propagates through the modified medium. In effect, the laser becomes part of the atmospheric disturbance. [RP Photonics+2Optica Publishing Group]rp-photonics.comthermal bloomingRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow…

What Is Thermal Blooming In Air Force Directed Energy Weapons? - Sky Command Brotherhood

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Why Self-Made Distortion Is Harder to Predict

Adaptive optics works best when distortions can be measured and corrected before they change significantly. Thermal blooming complicates this approach because the correction itself can alter the distortion.

When a deformable mirror sharpens a beam, the local intensity often increases. Higher intensity can produce stronger heating, which in turn generates stronger thermal blooming. Researchers have long recognised this feedback behaviour: improving focus can sometimes increase the very distortion that requires correction. [Panoptes]panoptesv.comPanoptes Thermal BloomingPanoptesThermal Blooming - How to Build a Laser Death RayThe gradient in air density acts like a weak lens that acts to defocus the beam…

The problem becomes even more difficult because thermal blooming is influenced by environmental variables that may change over the beam path:

  • Wind speed and direction.
  • Atmospheric absorption at the operating wavelength.
  • Humidity and aerosol content.
  • Beam power and dwell time.
  • Target tracking motion. [MDPI+2DEPS]mdpi.comAnalytical Study on the Steady-State Thermal Blooming of…by K Zhang · 2022 · Cited by 4 — In the present paper, we analytically st…

Wind illustrates the challenge particularly well. If air moves across the beam path, the heated air can be displaced to one side, creating an asymmetric refractive structure that steers the beam rather than simply defocusing it. Changes in wind direction can alter the distortion pattern substantially, forcing adaptive optics to chase a moving solution. Analytical studies of high-power beam propagation show that blooming behaviour can change dramatically when airflow direction changes, even if beam power remains constant. [MDPI]mdpi.comAnalytical Study on the Steady-State Thermal Blooming of…by K Zhang · 2022 · Cited by 4 — In the present paper, we analytically st…

Unlike many optical aberrations, thermal blooming is also nonlinear. Small increases in power do not necessarily produce proportionally small increases in distortion. As power rises, the atmosphere’s response can become increasingly complex, making prediction and compensation more difficult. [Optica Publishing Group+2RP Photonics]opg.optica.orgOptica Publishing GroupHigh-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 283 — In this article, we review…

Blooming Limits illustration 2

Why Conventional Adaptive Optics Faces a Feedback Problem

Traditional adaptive-optics systems were largely developed to correct externally imposed distortions, such as atmospheric turbulence affecting astronomical observations. In that setting, the atmosphere distorts the incoming light, the sensor measures the distortion, and the mirror applies a correction. The correction does not fundamentally change the atmosphere itself. [AIAA Journals]arc.aiaa.orgAIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and…by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial…

[thermal blooming]rp-photonics.comRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow… breaks this assumption.

The optical path is no longer a passive medium. Instead, it evolves in response to the beam’s own energy deposition. By the time a wavefront sensor measures the distortion and commands a mirror correction, the thermal structure may already be changing. The adaptive-optics loop is therefore attempting to control a system whose behaviour depends on the correction being applied. [DSpace+2ResearchGate]dspace.mit.edu31359954 MITAdaptive Optics for High Energy Laser Systemsby JE Wall · 1994 · Cited by 2 — High-energy laser propagation in the atmosphere requi…

This creates several operational difficulties:

Measurement lag. Sensors observe the distortion after it has developed, while heating continues during propagation. [AIAA Journals]arc.aiaa.orgAIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and…by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial…

Coupled phase and intensity effects. Adaptive optics is fundamentally a wavefront-control technology. Severe thermal blooming can create not only phase distortions but also intensity redistribution across the beam, which is harder for phase-only correction systems to address. [bqpsim.com]bqpsim.comAt this distortion level, density gradients create…Read more…

Changing correction targets. The optimal correction at one moment may become suboptimal seconds or milliseconds later as heating patterns evolve. [MDPI]mdpi.comAnalytical Study on the Steady-State Thermal Blooming of…by K Zhang · 2022 · Cited by 4 — In the present paper, we analytically st…

These factors explain why thermal blooming is often discussed separately from conventional turbulence correction even though both involve refractive-index variations in air. [AIAA Journals+2ResearchGate]arc.aiaa.orgAIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and…by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial…

Why Is Atmospheric Propagation Important For Air Force Directed Energy Weapons?

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Where Adaptive Correction Helps

Thermal blooming is not immune to adaptive optics. Experimental and modelling work has repeatedly shown that wavefront correction can recover part of the lost beam quality and increase energy concentration at the target under many conditions. Closed-loop adaptive-optics systems have demonstrated meaningful improvements in beam focus and far-field intensity when blooming levels remain within manageable ranges. [ResearchGate]researchgate.netResearchGate(PDF) Adaptive Optics for Reduction of Thermal Blooming…June 5, 2020 — The use of an AO system for the reduction of therma…Published: June 5, 2020

Adaptive optics is most effective when: [arc.aiaa.org]arc.aiaa.orgAIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and…by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial…

[thermal blooming]rp-photonics.comRP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow… ng is moderate rather than extreme.

  • Atmospheric conditions are reasonably stable.
  • Adequate wavefront information is available.
  • Control-loop speed is sufficient to track evolving distortions. [ResearchGate+2AIAA Journals]researchgate.netResearchGate(PDF) Adaptive Optics for Reduction of Thermal Blooming…June 5, 2020 — The use of an AO system for the reduction of therma…Published: June 5, 2020

In practical beam-control architectures, adaptive optics is therefore often treated as one component of a broader mitigation strategy rather than a standalone solution. Laser wavelength selection, power management, beam combining methods, engagement geometry, and atmospheric monitoring all influence blooming severity before the adaptive-optics system attempts correction. [DEPS]deps.orgJV2N1P5 SprangleOptimum Wavelength and Power for Efficient Laser…by P Sprangle · 2006 · Cited by 78 — The main objective is to discuss the optimum…

Blooming Limits illustration 3

Where Smart Mirrors Still Fall Short

The central limitation is that adaptive optics cannot eliminate the physical mechanism creating the distortion. It can reshape the wavefront entering the atmosphere, but it cannot stop the atmosphere from absorbing energy and heating up.

As blooming strength increases, the beam can experience distortions that exceed what practical deformable mirrors and control algorithms can compensate. Some studies note that beyond certain distortion levels, phase-only correction becomes increasingly ineffective because the beam suffers both phase and amplitude degradation rather than simple wavefront errors. [bqpsim.com]bqpsim.comAt this distortion level, density gradients create…Read more…

Another challenge is scale. Thermal blooming can develop over long propagation paths extending kilometres through the atmosphere. The resulting refractive structures may evolve continuously along the beam route rather than appearing as a single optical error that can be cancelled by one mirror correction. [Optica Publishing Group+2AFIT]opg.optica.orgOptica Publishing GroupHigh-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 283 — In this article, we review…

For directed-energy applications, this means adaptive optics can substantially improve performance but cannot guarantee that increasing laser power will always translate into proportionally greater target irradiance. At sufficiently high powers, the atmosphere increasingly becomes part of the weapon system itself, imposing limits through self-induced distortion. [Optica Publishing Group+2AIAA Journals]opg.optica.orgOptica Publishing GroupHigh-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 283 — In this article, we review…

Why Thermal Blooming Remains a Persistent Limit

Thermal blooming continues to challenge adaptive optics because it is fundamentally a feedback phenomenon. The beam heats the air, the heated air distorts the beam, and any corrective action can alter the heating pattern that produced the distortion in the first place. This differs from ordinary turbulence correction, where the atmosphere and the correction system are largely separate.

As a result, adaptive optics can reduce thermal-blooming losses, sometimes substantially, but it cannot fully escape the underlying physics. The higher the laser power and the longer the atmospheric path, the more the correction system must contend with a distortion that is continuously being generated by the beam itself. That self-created, evolving optical environment is why thermal blooming remains one of the most stubborn constraints on high-energy laser propagation. [AIAA Journals+2Optica Publishing Group]arc.aiaa.orgAIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and…by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial…

How Does Atmospheric Propagation Affect Air Force Directed Energy Weapons? - Sky Command Brotherhood

Channel: Sky Command Brotherhood

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Endnotes

  1. Source: rp-photonics.com
    Title: thermal blooming
    Link: https://www.rp-photonics.com/thermal_blooming.html
    Source snippet

    RP PhotonicsThermal Bloomingby R Paschotta · 2023 — Thermal blooming is a physical phenomenon associated with the propagation of high-pow...

  2. Source: opg.optica.org
    Link: https://opg.optica.org/ao/abstract.cfm?uri=ao-54-31-f201
    Source snippet

    Optica Publishing GroupHigh-power [lasers]({{ 'lasers/' | relative_url }}) for directed-energy applicationsby P Sprangle · 2015 · Cited by 283 — In this article, we review...

  3. Source: arc.aiaa.org
    Link: https://arc.aiaa.org/doi/10.2514/1.J061766
    Source snippet

    AIAA JournalsAdaptive Optics for Directed Energy: Fundamentals and...by RB Holmes · 2022 · Cited by 25 — Adaptive optics are beneficial...

  4. Source: afit.edu
    Link: https://www.afit.edu/bios/publications/Atmospheric_Prop_of_HEL.pdf
    Source snippet

    relevance to laser propagation in the atmosphere gains importance as laser's become...Read more...

  5. Source: mdpi.com
    Link: https://www.mdpi.com/2073-4433/13/10/1678
    Source snippet

    Analytical Study on the Steady-State Thermal Blooming of...by K Zhang · 2022 · Cited by 4 — In the present paper, we analytically st...

  6. Source: researchgate.net
    Link: https://www.researchgate.net/publication/307435846_Atmospheric_Propagation_of_High-Energy_Laser_Beams
    Source snippet

    Thermal blooming is manifest as strong distortions of laser beams that were first. detected in beam propagation...Read more...

  7. Source: researchgate.net
    Title: 361926577 Adaptive Optics for Directed Energy Fundamentals and Methodology
    Link: https://www.researchgate.net/publication/361926577_Adaptive_Optics_for_Directed_Energy_Fundamentals_and_Methodology
    Source snippet

    Adaptive Optics for Directed Energy: Fundamentals and...Jul 7, 2022 — Adaptive optics and related wavefront correction technologies have...

  8. Source: deps.org
    Title: JV2N1P5 Sprangle
    Link: https://www.deps.org/DEPSpages/JDE/JV2N1P5-Sprangle.pdf
    Source snippet

    Optimum Wavelength and Power for Efficient Laser...by P Sprangle · 2006 · Cited by 78 — The main objective is to discuss the optimum...

  9. Source: scholar.afit.edu
    Link: https://scholar.afit.edu/cgi/viewcontent.cgi?article=1774&context=facpub%2F1000
    Source snippet

    AFIT ScholarAtmospheric Propagation of High Energy Lasers: Thermal...Thermal blooming is a well documented phenomenon [15], whose releva...

  10. Source: bqpsim.com
    Link: https://www.bqpsim.com/articles/directed-energy-optics-optimization
    Source snippet

    At this distortion level, density gradients create...Read more...

  11. Source: researchgate.net
    Link: https://www.researchgate.net/publication/354911867_Numerical_simulation_of_high-energy_laser_propagation_through_the_atmosphere_and_phase_correction_based_on_adaptive_optics
    Source snippet

    Numerical simulation of high-energy laser propagation...The aim of this study is to maximize the [efficiency]({{ 'efficiency/' | relative_url }}) of the HEL through an accura...

  12. Source: researchgate.net
    Link: https://www.researchgate.net/publication/342088378_Adaptive_Optics_for_Reduction_of_Thermal_Blooming_Effects_by_Phase_Compensation
    Source snippet

    ResearchGate(PDF) Adaptive Optics for Reduction of Thermal Blooming...June 5, 2020 — The use of an AO system for the reduction of therma...

    Published: June 5, 2020

  13. Source: researchgate.net
    Link: https://www.researchgate.net/publication/235041191_Atmospheric_Propagation_of_High_Energy_Lasers_Modeling_Simulation_Tracking_and_Control
    Source snippet

    (PDF) Atmospheric Propagation of High Energy LasersIn most directed energy applications, laser beams propagate several kms in turbulent a...

  14. Source: opg.optica.org
    Link: https://opg.optica.org/oe/fulltext.cfm?uri=oe-34-7-12452
    Source snippet

    While adaptive optics (AO) technology...Read more...

  15. Source: opg.optica.org
    Link: https://opg.optica.org/abstract.cfm?uri=ao-29-21-3088
    Source snippet

    According to this model the...Read m...

  16. Source: opg.optica.org
    Link: https://opg.optica.org/ao/viewmedia.cfm?uri=ao-54-31-F201
    Source snippet

    optica.orgHigh-power lasers for directed-energy applicationsby P Sprangle · 2015 · Cited by 283 — In this article, we review and discuss...

  17. Source: researchgate.net
    Link: https://www.researchgate.net/publication/261574914_Thermal_blooming_of_laser_beams_along_atmospheric_paths_and_diagnostics_of_their_parameters
    Source snippet

    (PDF) Thermal blooming of laser beams along atmospheric...PDF | The paper describes results of theoretical investigation of high-power l...

  18. Source: youtube.com
    Title: Why Is Atmospheric Propagation Important For Air Force Directed Energy Weapons?
    Link: https://www.youtube.com/watch?v=ps0U7FxmwBE
    Source snippet

    "Thermal blooming" laser weapon adaptive optics Iron Beam In Fog: Can Laser Weapons Work Without Visibility? | WION Podcast WION...

  19. Source: panoptesv.com
    Title: Panoptes Thermal Blooming
    Link: https://panoptesv.com/SciFi/LaserDeathRay/ThermalBlooming.html
    Source snippet

    PanoptesThermal Blooming - How to Build a Laser Death RayThe gradient in air density acts like a weak lens that acts to defocus the beam...

  20. Source: dspace.mit.edu
    Title: 31359954 MIT
    Link: https://dspace.mit.edu/bitstream/handle/1721.1/35978/31359954-MIT.pdf
    Source snippet

    Adaptive Optics for High Energy Laser Systemsby JE Wall · 1994 · Cited by 2 — High-energy laser propagation in the atmosphere requi...

  21. Source: Wikipedia
    Title: Thermal blooming
    Link: https://en.wikipedia.org/wiki/Thermal_blooming
    Source snippet

    Thermal bloomingThermal blooming or thermal lensing occurs when high-energy laser beams propagate through a medium. It is the result o...

  22. Source: ui.adsabs.harvard.edu
    Link: https://ui.adsabs.harvard.edu/abs/2021JKPS…79..918A/abstract
    Source snippet

    The aim of this study is to maximize the...

Additional References

  1. Source: navysbir.us
    Link: https://navysbir.us/n13_1/N131-076.htm
    Source snippet

    Advanced Adaptive Optics (AO) for Laser Weapons in...OBJECTIVE: Develop a beaconless adaptive optic system capable of correcting moderat...

  2. Source: semanticscholar.org
    Link: https://www.semanticscholar.org/paper/Adaptive-optics-for-high-energy-laser-systems-Wall/d1083341f527f7d64d91a8e8f99877a01b9e5ab2

  3. Source: youtube.com
    Title: How Does Atmospheric Propagation Affect Air Force Directed Energy Weapons?
    Link: https://www.youtube.com/watch?v=LY8od8N_bPo
    Source snippet

    OSC Colloquium Mark Spencer: "High Energy Laser Perspectives from a Former Government Leader and..."...

  4. Source: scispace.com
    Title: Atmospheric Propagation of High Energy Lasers
    Link: https://scispace.com/pdf/atmospheric-propagation-of-high-energy-lasers-thermal-1o2y3rvtu5.pdf
    Source snippet

    High Energy Laser (HEL) propagation through turbulent atmosphere is examined via numerical simula- tion. The beam propagation is modeled...

  5. Source: pathfinderdigital.com
    Title: Path Finder Self-Defocusing/Thermal Bloom
    Link: https://www.pathfinderdigital.com/self-defocusing-thermal-bloom
    Source snippet

    PathFinderSelf-Defocusing/Thermal Bloom - Pathfinder DigitalSep 3, 2025 — Adaptive optics interactions: While adaptive optics correct tur...

  6. Source: inss.ndu.edu
    Title: laser focusing defense capabilities
    Link: https://inss.ndu.edu/news/Article/4412653/laser-focusing-defense-capabilities/
    Source snippet

    ndu.eduLaser-focusing Defense CapabilitiesHigh-energy laser systems could also potentially incur thermal damage to vulnerable satellite c...

  7. Source: youtube.com
    Link: https://www.youtube.com/watch?v=yN-QdZFW6zk
    Source snippet

    Why Is Atmospheric Propagation Important For Air Force Directed Energy Weapons?...

  8. Source: pubs.aip.org
    Title: This is due to atmospheric absorption and thermal.Read more
    Link: https://pubs.aip.org/aip/acp/article-pdf/766/1/58/11525647/58_1_online.pdf
    Source snippet

    Propagation of High Energy Lasers and...by JR Cook · 2005 · Cited by 33 — A major limitation of DF laser technology, however, was for sh...

  9. Source: youtube.com
    Title: Iron Beam In Fog: Can Laser Weapons Work Without Visibility? | WION Podcast
    Link: https://www.youtube.com/watch?v=7J2NJLBVER8
    Source snippet

    How Does Atmospheric Propagation Affect Air Force Directed Energy Weapons? - Sky Command Brotherhood...

  10. Source: youtube.com
    Title: What Is Thermal Blooming In Air Force Directed Energy Weapons?
    Link: https://www.youtube.com/watch?v=SQqoZHOzY1k
    Source snippet

    Iron Beam In Fog: Can Laser Weapons Work Without Visibility? | WION Podcast...

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