To a brief summary

E. Verroi and G. Naletto

The main problem is the instability of count rates in the 4 channels

Bad possibility of pointing the star ( since we are “blind” )

Low focusing control

Great noise contribution for long periods variable objects

Why Why ??

First hypothesis...

Shape of the beam section on the first lens of the optical train

for a well centred source

First hypotesis...In this case we would see differences beetween the 4 channels BUT stability in the global countrate (4 ch sum)

THERE IS ANOTHER PROBLEM

...Another instrument...Another instrument

Only two stars have been analyzed (gzccnc216-pg0911)

We don’t know the sky conditions for these 2 acquisitions

Neither their positions in the sky

A time tagging photon counting array returns data like this:

Pg are about 4 times brighter than gz but their noise (thermal + sky ) is about half.

Integration of the signal over 20 minutes of acquisition

Gz-kind star and Pg-kind star

Data analysisData analysis

Data Data analysisanalysis Pg: x 3.6”--- y 3.9”Pg: x 3.6”--- y 3.9”

Gz: x 2,4” --- y 2,5”Gz: x 2,4” --- y 2,5”

Gaussian fit FWHMGaussian fit FWHM

Look out Look out

!! This is not the seeing !!!! This is not the seeing !!

During the whole acquisition (20 min for each star) an optical system with the aperture of AQuEYE (3 arcsec entrance

diameter) would acquire only:

53%53% for gz

33%33% for pg

In the worst case an 8” pinhole is necessary to collect about 90% of the photons during the acquisition!

Fraction of collected photons as function of the pinhole diameter for Pg0911

This is the This is the seeing:seeing:Binning the data we can simulate the seeing

pg0911 with integration time = 0.5 s

Pg 3s T-bin Pg 1s T-bin Pg 0.5 s T-bin

Pg 0.25s T-bin Gz 8s T-bin Gz 1s T-bin

Only a part of the problem is caused by auto guidance system.

Centroid position of the star for 8s time bin for pg0911

The auto guide jumps are of the order of 0.5” but also with a “perfect” guide we don’t collect enough photons:

Fraction of photons collected as a function of the entrance aperture angular diameter for several measurements of seeing for a perfect

guiding and well pointed instrument

For this reason we choose to increase the pinhole dimension for IQuEYE as we will see later

Simulation of the signal Simulation of the signal for the four SPADs as for the four SPADs as

AQuEYE would see it...AQuEYE would see it...

original

simulated

IQUEYE

The Italian Quantum Eye for NTT/TNG

Assumptions:Telescope: focal length = 38.5 m; focal plane scale factor = 187 µm/arcsec; f/10.85

Assumed FoV to be collected: 5 arcsec = 0.935 mm on telescope focus

Needed total magnification (100 µm diameter SPAD): smaller than 1/10

IQUEYE Optical Concept

It has been considered a focal reducer with two couple of lenses, with a magnification of 1/3.25, and reducing a 5” telescope image (935 µm) to 290 µm (FWZH).Then, a pyramid splits the beam in four arms, and the following lenses further magnify the spot by 1/3.6, bringing the 5 arcsec spot size to 80 µm diameter (geometric magnification).

Focal reducer

Aqueye like single arm

IQUEYE Optical Performance

The The endend

The The endend

Summary of preceding Summary of preceding episodes...episodes...The aim of this activity is to realize a “prototype” of the instrument QuantEYE,

proposed for application to the focal plane of OWL .

QuantEYE is a very fast photometer, dedicated to the observation of celestial targets in the photon counting regime at 1 GHz max count rate

Our resources: 182 cm Ekar telescope in Asiago mounting AFOSC (Asiago Faint Object Spectrograph and Camera )

AFOSC is a focal plane instrument applied to the telescope focus

with which the beam is collimated, filtered/dispersed (grism)

and refocused (with a 0.58 magnification).

Summary of preceding Summary of preceding episodes...episodes...Owing to the limitations we have on available resources, we decided to subdivide the telescope pupil in only four parts ( instead of the 100 previewed for QuantEYE ) focusing each of them on a dedicated 50 m SPAD detector.

Summary of preceding Summary of preceding episodes...episodes... Specular Pyramid:Specular Pyramid:

Couples of Doublets:Couples of Doublets:

Focus the beam on the Focus the beam on the SPAD’s detectorSPAD’s detector

S.P.A.D.S.P.A.D.

Single photon Single photon avalanche diodeavalanche diode

Optional Optional FiltersFilters

AFOSC focusAFOSC focusSplits the beam Splits the beam in four parts in four parts towards each towards each SPADSPAD

Summary of preceding Summary of preceding episodes...episodes...

Our optics send a 180 m spot covering the whole pin-hole in 50 m in the image plane.

50 m is the spad’s detectors diameter

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