The Central Laser Facility is located near the middle of the Pierre Auger
Observatory in Argentina. It features a UV laser and optics that direct a beam
of calibrated pulsed light into the sky. Light scattered from this beam
produces tracks in the Auger optical detectors which normally record nitrogen
fluorescence tracks from cosmic ray air showers. The Central Laser Facility
provides a "test beam" to investigate properties of the atmosphere and the
fluorescence detectors. The laser can send light via optical fiber
simultaneously to the nearest surface detector tank for hybrid timing analyses.
We describe the facility and show some examples of its many uses.Comment: 4 pages, 5 figures, submitted to 29th ICRC Pune Indi

Arqueros, F.

Bellido, J.

Covault, C.

D'Urso, D.

Di Giulio, C.

Facal, P.

Fick, B.

Guarino, F.

Malek, M.

Matthews, J.

Matthews, J.A.J.

Meyhandan, R.

Monasor, M.

Mostafa, M.

Petrinca, P.

Roberts, M.

Sommers, P.

Travnicek, P.

U., /Utah

Valore, L.

Verzi, V.

Wiencke, Lawrence

English

arXiv

The Central Laser Facility is located near the middle of the Pierre Auger Observatory in Argentina. It features a UV laser and optics that direct a beam of calibrated pulsed light into the sky. Light scattered from this beam produces tracks in the Auger optical detectors which normally record nitrogen uorescence tracks from cosmic ray air showers. The Central Laser Facility provides a test beam  to investigate properties of the atmosphere and the uorescence detectors. The laser can send light via optical ber simultaneously to the nearest surface detector tank for hybrid timing analyses. We describe the facility and show some examples of its many uses

F. Arqueros

J. Bellido

C. Covault

C. Di Giulio

P. Facal

B. Fick

F. Guarino

M. Malek

J. A. J. Matthews

J. Matthews

R. Meyh

M. Monasor

M. Mostafa

P. Petrinca

M. Roberts

P. Sommers

P. Travnicek

L. Valore

V. Verzi

L. Wiencke

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The Central Laser Facility at the Pierre Auger Observatory

The Central Laser Facility is located near the middle of the Pierre Auger Observatory in Argentina. It features a UV laser and optics that direct a beam of calibrated pulsed light into the sky. Light scattered from this beam produces tracks in the Auger optical detectors which normally record nitrogen fluorescence tracks from cosmic ray air showers. The Central Laser Facility provides a ''test beam'' to investigate properties of the atmosphere and the fluorescence detectors. The laser can send light via optical fiber simultaneously to the nearest surface detector tank for hybrid timing analyses. We describe the facility and show some examples of its many uses

UNT (University of North Texas) Digital Library

29th International Cosmic Ray Conference Pune (2005) 00, 101–106The Central Laser Facility at the Pierre Auger ObservatoryF. Arqueros, J. Bellido, C. Covault, D. D’Urso, C. Di Guilio, P. Facal, B. Fick, F. Guarino,M. Malek, J.A.J. Matthews, J. Matthews, R. Meyhandan, M. Monasor, M. Mostafa,P. Petrinca, M. Roberts, P. Sommers, P. Travnicek, L. Valore, V. Verzi, L. Wienckefor the Pierre Auger Collaboration.Presenter: (M. Malek malek@fnal.gov usa-malek-M-abs1-he15-poster)The Central Laser Facility is located near the middle of the Pierre Auger Observatory in Argentina. It featuresa UV laser and optics that direct a beam of calibrated pulsed light into the sky. Light scattered from this beamproduces tracks in the Auger optical detectors which normally record nitrogen fluorescence tracks from cosmicray air showers. The Central Laser Facility provides a ”test beam” to investigate properties of the atmosphereand the fluorescence detectors. The laser can send light via optical fiber simultaneously to the nearest surfacedetector tank for hybrid timing analyses. We describe the facility and show some examples of its many uses.1. IntroductionThe southern Pierre Auger Observatory in Mendoza Province, Argentina measures extensive air-showers pro-duced by cosmic rays. A surface detector (SD) records the distribution of charged particles at ground level. Afluorescence detector (FD), consisting of independent eyes operating at night, records light profiles of showersas they develop in the atmosphere. The FD makes a calorimetric measurement of shower energy because theamount of fluorescence light emitted is proportional to the energy deposited in the atmosphere.The Central Laser Facility (CLF) (Fig. 1) provides a laser generated “test beam” for the observatory. TheCLF tracks recorded by the FD eyes have several similarities to tracks generated by extensive air showers.The laser wavelength of 355 nm is near the middle of the air shower fluorescence spectrum. After accountingfor atmospheric effects, the total amount of light scattered out of the beam is proportional to the laser beamenergy. At full laser energy, the amount of light scattered out of the beam is roughly equivalent to the amountof fluorescence light emitted by showers with energy in region of sensitivity of the FD to the predicted GZKFigure 1. The Central Laser Facility at the Pierre Auger Southern Observatory.FERMILAB-CONF-05-291-E-TD2 F. Arqueros et al.Figure 2. The major components of the CLF.suppression. The CLF can direct light simultaneously into a SD tank via optical fiber to test the relative timingbetween the FD and SD. The facility also houses a weather station and a radiometric cloud detector [1].2. Hardware DescriptionThe heart of the system is a frequency tripled YAG laser producing a 7 ns pulsed beam with a maximumenergy per pulse of 7 mJ. The optical configuration (Fig. 2) includes two harmonic separator mirrors arrangedso that the spectral purity of the 355 nm beam sent to the sky is better than 99.9%. A “flip mirror” selectsbetween two vertical beam paths. One goes directly to the sky when a simple cover is open. The other entersa mechanism with two mirrors on rotating orthogonal axes that can steer the beam in any direction above thehorizon. A mechanical cover protects the steering apparatus when not in use. The redundancy of this dualbeam configuration increases system reliability and simplifies operation.The beams are calibrated and configured with randomized polarization. The symmetric scattering propertiesof a depolarized beam are desirable: in this case a vertical beam scatters light equally in the direction of eachFD eye. Depolarizers in each beam path convolve the linearly polarized beam emitted by the laser to an outputbeam for which the net polarization is within 3% of random. The relative energy of each pulse is monitoredby a photo-diode detector. A pyroelectic energy probe, installed in March 2005, makes a second relativemeasurement of the vertical beam energy. This probe, factory calibrated to NIST standards, is used to calibratethe photo-diode probe in terms of energy delivered to the sky. This procedure is performed several times peryear. Energy and polarization calibrations are performed downstream of the last optical element before thebeams enter the sky.The Central Laser Facility... 3FD time bins0 100 200 300 400 500 600 700 800 900 1000photons/(m^2 time bin)050100150200250300350Real ProfileSimulated ProfileFigure 3. Simulated and measured FD detector re-sponse to a vertical CLF laser shot. The detailed simu-lation in this example includes a complete model of thedetector optics, pixel elements, and reflective triangularinserts between pixels. One FD time bin is 100 ns.80 90 100 110 120 130 140 150 160010002000300040005000µsphotons per µs at aperturedatasimulationFigure 4. Light profile at the aperture of the Los LeonesFD of a vertical CLF laser shot recorded under ex-tremely clear atmospheric conditions. This simplifiedsimulation assumes an aerosol-free atmosphere. Thehorizontal axis corresponds to the time since the laserfired.The CLF is solar powered, housed in a modified shipping container, and operated remotely via microwaveInternet link. The facility is unmanned. No wires run to the CLF. A small computer (PC) monitors the solarpower system, collects weather station and cloud detector data, and operates the laser system. All of thecontrol software is written using standard C programming tools. The PC which consumes 5 watts, runs a 25MB version of embedded Linux, and has no moving parts. Each time the laser is fired, the time, relative energy,beam path ID, and direction are recorded to a compact flash card. All data are copied off-site daily.The laser firing time relative to the GPS second is controlled by a programmable timing module [2]. Everyshot is tagged to avoid confusion with possible neutrino-generated upward going tracks. A small fraction of thelaser light can be injected into the nearest SD water tank (dubbed “Celeste”) via optical fiber. The “sky-only”shots are recorded by each triggered FD to a special laser file. The “sky+Celeste” shots are written to the samedata stream as air shower candidates together with the corresponding data from the Celeste tank.Laser operation is conducted from the observatory’s central campus by starting and stopping the control pro-gram at the beginning and end of each night of FD operation. Sets of 50 fixed-direction vertical shots are firedevery 15 minutes followed by one sky+Celeste shot. Patterns of inclined shots are also fired during two one-hour periods each night. This pattern include shots fired along the bisector angles between FDs and low-energynear-horizontal shots fired over each FD eye.3. Examples of UseOn nights scheduled for FD operation, the observation of CLF tracks provides real-time confirmation that theFD eyes are functioning and are able to “see” the array center. Shots fired into the sky and the Celeste tankare used to monitor the relative timing between the FD and the SD [3]. A fit to the longitudinal profile ofvertical tracks recorded by the FDs has been normalized to a clear air profile to generate an hourly data baseof aerosol optical depth measurements [4]. CLF shots are used in ongoing studies of triggering efficiency,geometrical reconstruction and the details of the FD pixel-pixel response (Fig. 3). Sweeps of inclined shotsare also used to test the FD mirror pointing directions. Work in progress compares the profiles of CLF verticaltracks recorded under extremely clear atmospheric conditions to simulated profiles assuming an aerosol-free4 F. Arqueros et al.CLF)/ECLF-ELL(E-0.3 -0.2 -0.1 0 0.1 0.2 0.3Events05101520253035April 21December 12a)April 21(-0.11 +/- 0.02) December 12(-0.16 +/- 0.03) CLF)/ECLF-ECO(E-0.3 -0.2 -0.1 0 0.1 0.2 0.3Events051015202530April 21December 12b)April 21(-0.04 +/- 0.02)December 12(-0.05 +/- 0.03)  (mJ)LLE4 5 6 7 (mJ)COE4567 c)April 21December 12)/2)CO+ELL)/((ECO-ELL(E-0.3 -0.2 -0.1 0 0.1 0.2 0.3Events051015202530354045April 21December 12d)April 21(-0.08 +/- 0.02)December 12(-0.12 +/- 0.02) Figure 5. A vertical beam from the CLF is used in a global cross-check of photometric calibration for two nights with ex-tremely clear viewing conditions. This cross-check involves two FD eyes, the CLF, the molecular atmospheric description,and 60 km of total light path. The consistency in the measured and reconstructed CLF energies is at the level of 15% (a,b).The correlation in laser energy as reconstructed by the Coihueco (CO) and Los Leones (LL) eyes (c,d) demonstrates thesensitivity of this test. The results are consistent with the current level of uncertainty in the calibrations of the elementstested including the atmosphere.atmospheric model. (Fig. 4). These comparisons are used to cross-check the calibration of the fluorescencetelescopes (Fig. 5). This work tests, in combination, the photometric calibration of the CLF and two FD eyes,the identification of clear conditions, and modeling of molecular atmospheric conditions over a total light pathdistance of 60 km.References[1] D. Riordan et al. J. Geophys. Res., 110, D03207, (2004).[2] J.D. Smith, S. B. Thomas, L. R. Wiencke et al., Proc of 27th ICRC, HE175, (2001).[3] J. Bellido et al., Proc of 29th ICRC, HE 1.5 (2005).[4] R. Cester et al., Proc of 29th ICRC, HE 1.5 (2005).

The Central laser facility at the Pierre Auger Observatory

The Central Laser Facility is located near the middle of the Pierre Auger Observatory in Argentina. It features a UV laser and optics that direct a beam of calibrated pulsed light into the sky. Light scattered from this beam produces tracks in the Auger optical detectors which normally record nitrogen fluorescence tracks from cosmic ray air showers. The Central Laser Facility provides a "test beam" to investigate properties of the atmosphere and the fluorescence detectors. The laser can send light via optical fiber simultaneously to the nearest surface detector tank for hybrid timing analyses. We describe the facility and show some examples of its many uses

The Central Laser Facility at the Pierre Auger Observatory

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