ThermalBlooming

MATLAB

[TB,TBPhase] = ThermalBlooming(Method,lambda,Pwr,Focus,D,...
                              Type,S,Atm,[P1,P2,...PN])
[TB,TBPhase] = ThermalBlooming(Method,Laser,S,Atm,[P1,P2,...PN])

Description

Computes the effect of thermal blooming using the specified analysis method for the propagation scenario described by the inputs. The optional input parameters P1, P2, P3,..., PN are those required for the analysis method. Currently supported analysis methods are 'SCALING' and 'WAVEOPTICS'.

'SCALING' method computes angular peak shift, beam spread (relative to diffraction), and Strehl ratio using empirical scaling laws derived from wave optics modeling of thermal blooming effects for a Gaussian or Uniform beam. The output structure TB contains metrics for modeling the incident irradiance. The output structure TBPhase has the same form as TB, but models the effect of thermal blooming on the phase and would be applicable to cases where the incident irradiance is propagated to a focus, e.g. relay uplinks. TB.StrehlA is based on a fit of a calculated distortion parameter to the amount of increase in beam area from the diffraction-limited case. TB.StrehlB is based on the amount of increase in the beam dimensions (SprdP and SprdT). The two methods have been shown to give approximately equal Strehl ratio. In the case of an 'UNIFORM' beam, the scaling parameter for calculation of Strehl is TB.NdIpk (from DistortionNumber). TB.PkShiftP is calculated based on the parameter TB.NcPkShft (from DistortionNumber called with Focus = inf). For 'GAUSSIAN,' all calculations use Nd, and so TB.NdIpk and TB.NcPkShft will be returned as [].

'WAVEOPTICS' method computes thermal blooming beam metrics via a wave-optics simulation of steady-state thermal blooming. Uses the basic function TBWaveCalc for calculation. Propagation parameters can be controlled through a 'PropControl' input as in TBWaveCalc. If propagation control is not exercised, the simulation parameters will be automatically computed given other inputs.

NOTE: The thermal blooming Strehl ratio reported by the 'SCALING' method is the peak irradiance relative to a beam propagated through vacuum, but experiencing the same attenuation (absorption/scattering) as through the blooming volume. Multiply by atmospheric transmission to compute the peak irradiance reduction relative to the vacuum peak irradiance.

Parameters

Parameters	Description
Method [string]	Identifier for analysis methodology (e.g., 'SCALING')
Laser [struct]	Structure from LaserField or a comma-separated list of (...lambda,Pwr,Focus,D,Type,...)
lambda [scalar]	Wavelength of laser (m)
Pwr [scalar]	Total power of laser through link (W)
Focus [scalar]	Range at which laser beam is focused (m)
D [scalar]	Starting diameter of laser (m)
Type [char]	Beam type, must be 'Gaussian' or 'Uniform'
S [struct]	Structure of engagement geometry parameters as from EngagementStruct
Atm [struct]	Atmospheric modeling parameters from AtmStruct. Atm must have wind profile if calculation with wind is desired.
P1...PN [list]	Additional parameters required for analysis method For 'SCALING' method, no additional parameters are needed. For 'WAVEOPTICS' method, an optional propagation control structure, PropControl (see TBWaveCalc)

Return Values

Return Values	Description
TB [struct]	Beam metrics associated with thermal blooming analysis with different fields depending on Method
TBPhase [struct]	Beam metrics associated with thermal blooming analysis on the phase of the incident irradiance with the same fields as TB. Not used for 'WAVEOPTICS' method.
Method	'SCALING' 'WAVEOPTICS', TB contains fields Irr, x, y, t, Ipk, Irel, Strehl, Shft, Sig, WaveOpt as documented in TBWaveCalc
TB.FocusRange [scalar]	Focus range used for computing effects of thermal blooming
TB.Nd [scalar]	Distortion number for focused laser beam in propagation path
TB.NdIpk [scalar]	Scaling parameter for estimation of peak irradiance
TB.Nc [scalar]	Distortion number for collimated laser beam in propagation path
TB.NdPkShft [scalar]	Scaling parameter for estimation of peak shift
TB.PkShiftP [scalar]	Angular shift of peak irradiance (rad)
TB.SprdP [scalar]	Beam spread in P axis relative to diffraction
TB.SprdT [scalar]	Beam spread in T axis relative to diffraction
TB.StrehlA [scalar]	Relative peak irradiance computed via method A above (based on NdIpk)
TB.StrehlB [scalar]	Relative peak irradiance computed via method B above (based on NdIpk)

References

M. R. Whiteley and V. S. R. Gudimetla, "Simulation and Analysis of Directed Energy Beam Control: Advanced Airborne Laser, Relay Mirror, and Tactical Laser," AFRL Technical Report, contract F29601-02-D-0256, July 2004.
A. M. Ngwele, "Scaling Law Modeling of Thermal Blooming in Wave Optics," MZA Technical Report, contract NGIT ABL A&AS, Nov 2010.

Examples

>> S = EngagementStruct(GeomStruct);

>> Atm = ChangeAtm(AtmStruct,'Ext',[],'Abs','MODFAS','A','1000', ...

'Scat','MODFAS','S','1000')

>> TB = ThermalBlooming('SCALING',1.0e-6,100e3, ...

S.L,1.0,'Gaussian',S,AtmStruct)

Thermal blooming for a Gaussian laser focused at the target using SCALING method. Default from AtmStruct has total extinction but the thermal blooming calculation needs absorption and scattering separately.

>> TB = ThermalBlooming('WAVEOPTICS',1e-6,100e3,S.L,1.0,'Gaussian',S,Atm)

Thermal blooming for a Gaussian laser focused at the target using WAVEOPTICS method.