effects of spatially inhomogeneous photomultiplier sensitivity on lidar signals and remedies

Effects of spatially inhomogeneous photomultiplier sensitivity…..http://www.freudenthaler.de/ILRC22

Effects of spatially inhomogeneous photomultiplier sensitivity on lidar signals and

remediesVolker Freudenthaler

Meteorologisches Institut der Universität München, Munich, Germany

R5600

V. Simeonov et al., Influence of the Photomultiplier Tube Spatial Uniformity on Lidar Signals, Appl. Opt. 38, 5186-5190 August 1999.


Hamamatsu PMT R5600 / R7400

included in modules:

•H57xx •H67xx•H7468•H7155•H7825•H7829

R7400

R5600R5600

old

new


MULIS - Multi Purpose Lidar System

from telescope500 mm

Optical design for 3 backscatter + 2 extinction + 1 depolarisation channel


POLIS - Portable Lidar System


Biaxial lidar model for ray tracing

Considered parameters

• axial distance of laser and telescope

• laser axis tilt

• laser divergence

• discrete ray source cross sections

• Software: ZEMAX-EE

Laser

Telescope


Focal spot positions

Laser

Telescope

Range angle of incidence

radial position of focal spots

5 km 150 m


Focal spot positions PMT

Laser

Telescope

Range angle of incidence radial position of focal spots

5 km 150 m


Image of tele-focus on PMT


Spot positions on PMT over range

Ratio to real signal


Radial shift of axis position on PMT

vertical and horizontal shift ±1 mm



Horizontal and vertical orientation of PMT

horizontal vertical

vertical

horizontal



Diffusor

Diffusor doesn't help

if not very far from PMT

high loss of signal intensity

bad especially for Raman channels

Spot PMT

rati

o t

o r

eal si

gnal


How to find the best PMT position

Telescope PM

Image of focusFocus

Imageof PM

large image of primary mirror (PM)

large PMT necessary



Focus

F2 F3

Telescope PM

Imageof PM



Focus

F2

Telescope PM

Imageof PM


Spot on PMT with eyepiece

150 m PMT-1 0 +1 mm


Spot on PMT with eyepiece over range

150 m PMT-1 0 +1 mm


Biaxial spots on PMT over range

– Spot does move

axial position 0 mm

Rati

o t

o r

eal si

gnal


Biaxial spots on PMT with eyepiece

+ Spot does not move

– change of intensity distribution

axial position 0 mm

Rati

o t

o r

eal si

gnal





axial position +1mm

Rati

o t

o r

eal si

gnal





axial position -1 mm

Rati

o t

o r

eal si

gnal


Eyepiece + diffusor


Eyepiece + diffusor + mirror tube

"Smart diffusor"


Biaxial spots on PMT with smart diffusor


+ no change of intensity distribution

axial position noncritical

Rati

o t

o r

eal si

gnal


Monoaxial spots on PMT



axial position 0 mm

Rati

o t

o r

eal si

gnal





axial position -1 mm

Rati

o t

o r

eal si

gnal





axial position +1 mm

Rati

o t

o r

eal si

gnal


Monoaxial spots on PMT with eyepiece

axial position 0 mm

Rati

o t

o r

eal si

gnal


+ little change of intensity distribution


Solutions

Diffusor Eyepiece Smart Diffusor

signal loss: high no low

design: simple ray tracing ray tracing

accuracy needs:

low high low

effort: low high high


Solutions

Diffusor Eyepiece Smart Diffusor

signal loss: high no low

design: simple ray tracing ray tracing

accuracy needs:

low high low

effort: low high high

mechanical accuracy: better than ± 1 mm

lens focal lengths: better than ± 1% (± 2% usual)

optical control of result necessary


End

Thank you for your attention!

effects of spatially inhomogeneous photomultiplier sensitivity on lidar signals and remedies

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