1 S. Maltezos XXIX Workshop on Recent Advances in Particle Physics and Cosmology - Patras 2011 S....

11 S. Maltezos S. Maltezos XXIX Workshop on Recent Advances in Particle Physics and CosmologyXXIX Workshop on Recent Advances in Particle Physics and Cosmology - - Patras 2011 Patras 2011

ATMOSPHERIC MONITORING FOR CHERENKOV TELESCOPE ARRAY ATMOSPHERIC MONITORING FOR CHERENKOV TELESCOPE ARRAY CTA: DEVELOPMENT OF A HSRL PROTOTYPE FOR SYNERGYCTA: DEVELOPMENT OF A HSRL PROTOTYPE FOR SYNERGY

WITH RAMAN LIDAR WITH RAMAN LIDAR

NTUA

National Technical University of AthensNational Technical University of Athens

E. FokitisE. Fokitis

S. MaltezosS. Maltezos

A. PapayannisA. Papayannis

A. AravantinosA. Aravantinos

V. GikaV. Gika

M. KompitsasM. Kompitsas

P. Fetfatzis P. Fetfatzis

N. MaragosN. Maragos

Y. Manthos Y. Manthos


OutlineOutline

VHE gamma ray astronomy & CTA observatoryVHE gamma ray astronomy & CTA observatory

Atmospheric monitoring for CTAAtmospheric monitoring for CTA

Design of a HSRL and synergy with RAMAN LidarDesign of a HSRL and synergy with RAMAN Lidar

Performance evaluation of a laser sourcePerformance evaluation of a laser source

Optical characterization of F-P etalon receivers Optical characterization of F-P etalon receivers

Conclusions and ProspectsConclusions and Prospects


VHE VHE -ray astronomy-ray astronomy

Some of scientific issues:Some of scientific issues:

Understand the High Energy cosmic phenomena and the relevant objects.

Identify the main cosmic accelerators, both galactic and extra galactic.

Search in extreme conditions for exotic phenomena implying new physics.

The VHE photons travelling through large distances are powerful probe of fundamental physics under extreme conditions.

Electromagnetic ProcessesElectromagnetic Processes

Synchrotron emissionSynchrotron emission

Inverse Compton scattering (IC)Inverse Compton scattering (IC)

BremsstrahlungBremsstrahlung

Hadronic CascadesHadronic Cascades

Decay of neutral pions produced by CRs interacting with the ambient gas.Decay of neutral pions produced by CRs interacting with the ambient gas.

p+p p+p ± ± + + 00+…+… e e± ± + + vv + + ……

Possible mechanisms producing Possible mechanisms producing γγ-rays:-rays:


Ground based observatoriesGround based observatories

Gamma-ray fluxes for E>1 TeV are typically of the order of 2x10-7 m-2s-1, and thus, large detection area (>105 m2) is required.

Some contemporary observatories using IACT

[ Alessandro De Angelis, INAF INFN/Univ. Udine & LIP/ISTECRS, Turku 2010 ]


The Imaging Atmospheric-Cherenkov TechniqueThe Imaging Atmospheric-Cherenkov Technique

[ Alessandro De Angelis, INAF INFN/Univ. Udine & LIP/ISTECRS, Turku 2010 ]

Cherenkov angle (Cherenkov angle (θθcc): ~1): ~100

Energy threshold: 21 MeV in NPT conditionsEnergy threshold: 21 MeV in NPT conditions

Maximum at 1 TeV shower: Height: 8 km, 200 photons/mMaximum at 1 TeV shower: Height: 8 km, 200 photons/m22 in the Visible in the Visible

Angular spread: 0.5Angular spread: 0.500

Using an array of telescopes we can Using an array of telescopes we can accomplish better:accomplish better:

background reduction of CRsbackground reduction of CRs

angular resolution (~arcmin at T1 eV)angular resolution (~arcmin at T1 eV)

energy resolution (~15 %)energy resolution (~15 %)

thr / ( 1)( 1) / 2( 1)o oE nE n n E n


The CTA ObservatoryThe CTA Observatory

The Cherenkov Telescope Array (CTA) is aThe Cherenkov Telescope Array (CTA) is a proposed advanced facility for ground based highproposed advanced facility for ground based high energyenergy gamma ray astronomygamma ray astronomy..

This approach hasThis approach has proven to be extremely successful for gamma raysproven to be extremely successful for gamma rays of energies above 100 GeV.of energies above 100 GeV.

The facility will consistThe facility will consist of an array of telescopes enhancing the all skyof an array of telescopes enhancing the all sky monitoring capabilitymonitoring capability and and using low, medium and high energy sections.using low, medium and high energy sections.


Atmospheric monitoring for CTAAtmospheric monitoring for CTA

The monitoring direction has to follow the event direction.The monitoring direction has to follow the event direction.

The contribution of the NTUA Team to the CTA experiment deals with the appropriate The contribution of the NTUA Team to the CTA experiment deals with the appropriate instrumentation for high-accuracy atmospheric monitoring.instrumentation for high-accuracy atmospheric monitoring.


Developing a multi-wavelength HSRLDeveloping a multi-wavelength HSRL

The The HSRL allows higher sensitivity in comparison with Raman LIDAR because of the HSRL allows higher sensitivity in comparison with Raman LIDAR because of the greater cross section of the interaction. greater cross section of the interaction.

The The effort now is to assemble a pulsed SLM coherent laser system at 355 nm. Via Raman effort now is to assemble a pulsed SLM coherent laser system at 355 nm. Via Raman cells it can provide additional UV and near UV wavelengths (multi-wavelength feature).cells it can provide additional UV and near UV wavelengths (multi-wavelength feature).

FabryFabry-Perot etalon pair is used to distinguish the signal contributions of aerosol and -Perot etalon pair is used to distinguish the signal contributions of aerosol and molecular scattering.molecular scattering.

The spectral region of the detector’s sensitivity The spectral region of the detector’s sensitivity practically, lies in the range about 325 - 525 nm.practically, lies in the range about 325 - 525 nm.

The spectral region of interest for multi-The spectral region of interest for multi-wavelength atmospheric monitoring can be wavelength atmospheric monitoring can be narrower, in the range 350 to 450 nm. narrower, in the range 350 to 450 nm.

higher night sky background


Spectral structure of the signalSpectral structure of the signal

The Lidar equation describing the backscattered signal by molecules (The Lidar equation describing the backscattered signal by molecules (mm) and aerosols ) and aerosols (particulates) ((particulates) (pp) in the atmosphere:) in the atmosphere:

The height of the measurement is pre-The height of the measurement is pre-selected by the timing of the detection. selected by the timing of the detection.

An accurate determination of the height An accurate determination of the height can be achieved using the correlation can be achieved using the correlation function between the transmitted and the function between the transmitted and the backscattered pulse.backscattered pulse.

Height determination:Height determination: Spectral discrimination:Spectral discrimination:

Backscattering Backscattering coefficientcoefficient Extinction coefficientExtinction coefficient

( ) ( ) ( ) ( ) ( )a aa a ma m aS r Q C r N r C r N r B

( ) ( ) ( ) ( ) ( )m am a mm m mS r Q C r N r C r N r B Signal compositionSignal composition


An indicative design of HSRL in An indicative design of HSRL in backscattering mode backscattering mode

Design configuration of HSRLDesign configuration of HSRL

(1) Light source (transmitter):(1) Light source (transmitter): pulsed, narrow line SLM laser at neat UV 355 nm + gas Raman cells (being developed)pulsed, narrow line SLM laser at neat UV 355 nm + gas Raman cells (being developed)

(2) Spectral discriminators (receivers):(2) Spectral discriminators (receivers): two, high overall finesse F-P etalons with different FSRs (being developed)two, high overall finesse F-P etalons with different FSRs (being developed)

(3) Receiver telescope:(3) Receiver telescope: mounting and rotation mechanism (prototype) + parabolic mirror, polishing quality ~mounting and rotation mechanism (prototype) + parabolic mirror, polishing quality ~λ/λ/88 (available)(available)

(4) Signal detectors:(4) Signal detectors: high-sensitivity LN-cooled CCD (available and recently tested) + UV band-pass optical filter (available)high-sensitivity LN-cooled CCD (available and recently tested) + UV band-pass optical filter (available)

Sub-systems and specification of a multi-wavelength HSRL:Sub-systems and specification of a multi-wavelength HSRL:

(1)(1)

(2)(2)

(3)(3)(4)(4)


HSRL in synergy with RAMANHSRL in synergy with RAMAN

Methodology schemeMethodology scheme

HSRL operation

Backscattered light signal separation

P(z)

Raman operation

AerosolAerosol

channelchannel

MolecularMolecular

channelchannel

Pm(z)

(z)

(z)

Sl(z)

m(z)

P,R,1(z)

=3=35555 nmnm

R,2R,2=407 =407 nmnm

´́=53=5322 nm, 355 nmnm, 355 nm

(z)

R,1R,1=3=38787 nmnm

P,R,2(z)

Lidar ratioLidar ratio

mixing ratio of water mixing ratio of water vapor to dry airvapor to dry air

The methodology illustrating the how to determine the optical The methodology illustrating the how to determine the optical parameters of the atmospheric constituentsparameters of the atmospheric constituents

the molecular number density of the reference gas (nitrogen) : extinction coefficient for aerosols at

: extinction coefficient for molecules at 0

: reference Raman signal

Re f

Re,0 ,02

,0

0

Ref

( )ln ( ) ( )

( )( )

1

fm a

z

a k

N zdz z

d P z zz

,0aa0,ma

Re fP

RAMAN:RAMAN: the signal depends on the signal depends on αα alonealone

HSRL: HSRL: the signalthe signal depends on both depends on both ββ and and αα

: the molecular volume-backscatter coefficient: the molecular extinction coefficient: the volume backscatter coefficient of aerosol and clouds: the Rayleigh backscatter power: the Mie backscatter power

2 ln( ( ) ) ( )1 1( ) ( )

2 2 ( )m m

a mm

d P z z d zz z

dz z dz

)(zPm

( )( ) ( )

( )a mm

P zz z

P z

1

( )( )

( )a

a

zS z

z

[A. ANSMANN, et al, Appl. Phys. B 55, 18-28 (1992) M. IMAKI, Y. TAKEGOSHI and T. KOBAYASHI, Japanese Journal of

Applied Physics Vol. 44, No. 5A, 2005, pp. 3063–3067]

( )m z( )m z

( )aP z

( )a z

Re f:N


RAMAN Lidar setup in NTUARAMAN Lidar setup in NTUA

Recently acquired Quanta Ray laser 1.2 J per pulse (not SLM) operating at 1064, 532 and 355 nm.

Option of injection seeding for frequency stabilization.

The NTUA Raman lidar with a multi-wavelength detection box at: 355-387 (nitrogen 1st Stokes)-407 (water vapor 1st stokes)-532-607 (water vapor 1st Stokes)-1064 nm.

RAMAN LIDAR setup of NTUA Atmospheric RAMAN LIDAR setup of NTUA Atmospheric Environment group with 300 mm telescopeEnvironment group with 300 mm telescope

If the seeder is funded, then it is feasible to operate in HSRL modeIf the seeder is funded, then it is feasible to operate in HSRL mode


Studying the laser mode competition Studying the laser mode competition

1.05 A 1.55 A 2.00 A

ΤΤest of Nd:YVOest of Nd:YVO44 DPSS CW DPSS CW

SLM Laser at 532 nm using a SLM Laser at 532 nm using a spectrum analyzer (scanning spectrum analyzer (scanning confocal F-P etalonconfocal F-P etalon 2 2 GHz GHz FSR).FSR).

Capture of the spectrum Capture of the spectrum analyzer signal analyzer signal observed at the observed at the oscilloscope.oscilloscope.

A recently purchased Nd:YVOA recently purchased Nd:YVO44 DPSS CW SLM Laser at 1064 nm DPSS CW SLM Laser at 1064 nm has to be converted to pulsed and has to be converted to pulsed and

amplified. In a subsequent stage a Second amplified. In a subsequent stage a Second HHarmonic armonic GGenerationeneration and a and a SSum um FFrequency requency MModeode will will used for providing the 355 nm beamused for providing the 355 nm beam..


Studying the frequency driftStudying the frequency drift

(1)(1) SLM CW DPSS Laser at 532 SLM CW DPSS Laser at 532 nmnm

(2)(2) Beam reflector ~4 % (glass) Beam reflector ~4 % (glass)(3)(3) Scanning confocal Fabry- Scanning confocal Fabry-

PerotPerot (4)(4) Laser Power Supply Laser Power Supply (5)(5) Digital Oscilloscope Digital Oscilloscope (6)(6) Sawtooth voltage generator Sawtooth voltage generator (7)(7) Voltage Amplifier Voltage Amplifier

The frequency drift rate, following an exponential-shape The frequency drift rate, following an exponential-shape curve by time, tends to zero.curve by time, tends to zero.

The SLM feature is achieved.The SLM feature is achieved.

After about 7 h (temperature stabilization) :After about 7 h (temperature stabilization) :


Molecular channel test at UV regionMolecular channel test at UV region

Experimental setup for testing molecular Experimental setup for testing molecular F-P etalon (F-P etalon (11) with spacer d=13.015 mm: ) with spacer d=13.015 mm: Use of mercury low pressure spectral Use of mercury low pressure spectral lamp (lamp (22) with a narrow filter () with a narrow filter (33) at 365 nm. ) at 365 nm.

A system of three fringe patterns A system of three fringe patterns corresponding to the triplet at 365 nmcorresponding to the triplet at 365 nm(3 transition lines spaced by 0.5 and 1 (3 transition lines spaced by 0.5 and 1 nm). nm).

2-D plot of intensity showing the three 2-D plot of intensity showing the three fringe system.fringe system.

2233

33

11

Triplet at 365 nmTriplet at 365 nm

Low pressure Low pressure mercury lampmercury lampspectrumspectrum


Evaluation of the etalon parallelismEvaluation of the etalon parallelism

The excess fraction (The excess fraction (εε) is determined) is determinedin a grid of x,y points. The variation in a grid of x,y points. The variation of of εε reflects the effective spacing reflects the effective spacing variation (parallelism defect) .variation (parallelism defect) .

x

y

The relative spacing The relative spacing variation for a variation for a commercial as a commercial as a reference (5 mm). reference (5 mm). Parallelism=Parallelism=λλ/50 (P-V)/50 (P-V)

The relative spacing The relative spacing variation of the etalon variation of the etalon under test (13 mm).under test (13 mm).Parallelism=Parallelism=λλ/4 (/4 (P-V)P-V)

2

d

Wavelength used: Wavelength used: λλ=435 nm)=435 nm)

DD=70 mm=70 mm


11stst stage of analysis: stage of analysis: determination of the “excess fractions” determination of the “excess fractions” ii

((ii=1,2) of the 2-D fringe pattern for both wavelengths. =1,2) of the 2-D fringe pattern for both wavelengths.

22ndnd stage of analysis: stage of analysis: optimum solution investigation algorithm in optimum solution investigation algorithm in the “Excess Fraction Space” by a novel method developed.the “Excess Fraction Space” by a novel method developed.

Determination of the Determination of the effectiveeffective spacing spacing

1 11

2 mod 1

d

2 22

2 mod 1

d

Modular equation system to be solved:Modular equation system to be solved:

)()( 2

2

2

1 ddr minmin

A precision of few nm is feasible ! A precision of few nm is feasible !

REQUIREMENT !REQUIREMENT !

At least two well-known lines (wavelengths At least two well-known lines (wavelengths 1 1 and and 2 2 with an accuracy of the order of with an accuracy of the order of

22××1010-8-8).).

2dm

Optimum solution for ´1 and ´2

Optimum-ideal solution for d

Modular Equation system

Optimum solution for d

Not feasibleNot feasible


Mounting type of receiversMounting type of receivers

Etalon for the molecular channel:Etalon for the molecular channel:

Mounting type proposed for this etalon (13 mm spacer):“Hansen mount” type applied at Dynamic Explorer Fabry-Perot made of “invar”.

[ T. Killean et al, Appl. Opt. 21, 3903-3912 (1982) ]

Etalon for the aerosol channel:Etalon for the aerosol channel:

Mounting system proposed of this etalon (100 mm spacer):a cylinder made of “zerodur”.


• A multi-wavelength in near UV HSRL design for atmospheric monitoring in CTA observatory is on the way at NTUA.

• The synergy of HSRL/RAMAN lidar promises higher accuracy of atmospheric monitoring, thus we are studying this possibility.

• The frequency stability and SLM feature of the tested CW laser is established after certain time of operation.

• Our methods for characterization of the F-P etalon receivers were verified and can help us for serious improvements.

• A near future prospect of our team is to accomplish funding for injection seeding to the Quanta Ray laser of 1.2 J per pulse for operating in HSRL mode.

Conclusions and ProspectsConclusions and Prospects


Backup transparenciesBackup transparencies


Determination of the effective spacing - 2Determination of the effective spacing - 2

1 S. Maltezos XXIX Workshop on Recent Advances in Particle Physics and Cosmology - Patras 2011 S....

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Transcript of 1 S. Maltezos XXIX Workshop on Recent Advances in Particle Physics and Cosmology - Patras 2011 S....