Photoinjector laser intensity and pointing position monitoring system
This work contains the description of a laser intensity and a laser beam pointing stability monitoring system, which was created for the Photo Injector Test Facility at Zeuthen, PITZ. The measurements are based on the usage of three detectors: a photomultiplier tube, a quadrant diode, and a coupled...
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| Published in: | Вопросы атомной науки и техники |
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| Date: | 2007 |
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Німецький Електронний-Синхротрон (DESY) Німеччини
2007
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| Cite this: | Photoinjector laser intensity and pointing position monitoring system / Y.Y. Ivanisenko// Вопросы атомной науки и техники. — 2007. — № 5. — С. 166-170. — Бібліогр.: 6 назв. — англ. |
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| citation_txt | Photoinjector laser intensity and pointing position monitoring system / Y.Y. Ivanisenko// Вопросы атомной науки и техники. — 2007. — № 5. — С. 166-170. — Бібліогр.: 6 назв. — англ. |
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| description | This work contains the description of a laser intensity and a laser beam pointing stability monitoring system, which was created for the Photo Injector Test Facility at Zeuthen, PITZ. The measurements are based on the usage of three detectors: a photomultiplier tube, a quadrant diode, and a coupled charge camera. Investigations were done for the nominal operation conditions: up to 800 laser pulses ( 20 psec duration) with a repetition rate of 1 MHz, a pulse energy of up to 30 microJ (wave length 262 nm), and a pulse train repetition rate is 10 Hz.
Описана система безперервного мониторингу стабільності інтенсивності та позиції катодного лазера фото-інжектора на установці випробування фото інжекторів у Цойтені, DESY. Вимірювання здійснюються фотоелектронним помножувачем, квадрантним фотодіодм та ПЗС. Вимірювання проводилися при нормальному режемі: 800 лазерних імпульсів тривалістю 20 пс з частотою слідуванния 1 МГц, энергія кожного импульсу до 30 мкДж, частота цугів 10 Гц.
Рассмотрена система, созданная для мониторинга стабильности положения и интенсивности импульсов излучения лазерной системы фото-инжектора PITZ. Измерения осуществляются с использованием трех детекторов: фотоэлектронного умножителя, квадрантного фотодиода и ПЗС камеры. Основное внимание уделено работе установки в номинальном режиме: 800 лазерных импульсов (длительность 20 пс с частотой повторения 1 МГц, энергия в одном импульсе до 30 мкДж, частота последовательностей 10 Гц.
|
| first_indexed | 2025-12-07T17:10:38Z |
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PHOTOINJECTOR LASER INTENSITY AND POINTING
POSITION MONITORING SYSTEM
Ye. Ye. Ivanisenko∗
Deutsches Elektronen Synchrotron, D-15738, Zeuthen, Germany
(Received March 28, 2007)
This work contains the description of a laser intensity and a laser beam pointing stability monitoring system, which
was created for the Photo Injector Test Facility at Zeuthen, PITZ. The measurements are based on the usage of three
detectors: a photomultiplier tube, a quadrant diode, and a coupled charge camera. Investigations were done for the
nominal operation conditions: up to 800 laser pulses ( 20 psec duration) with a repetition rate of 1 MHz, a pulse
energy of up to 30 microJ (wave length 262 nm), and a pulse train repetition rate is 10 Hz.
PACS: 07.60.-j, 42.79.-e
1. INTRODUCTION
The radio frequency electron photo injector is a
type of injectors, where the formation of the electron
bunch is based on the photocathode illumination with
short light pulse followed by electrons photoemission
and acceleration by a rf-field. For the purpose inten-
sive laser radiation is used.
The injector operation stability is investigated at
PITZ (Photo Injector Test facility in Zeuthen) in
Zeuthen, DESY, Germany [2]. The repetitional rate
of the RF-power pulses is 10 Hz, and of the laser
pulses is 1MHz. The RF-power flat top pulse dura-
tion is 0.8 ms (klystron output power 4 MW), that
gives opportunity to produce up to 800 bunches.
2. DIAGNOSTICS SYSTEM
The role of the photoinjector is the generation of
high brilliance and small emittance electron bunches
for FEL application. For this purpose the generation
is based on the photoemission of the Cs2Te cathode
[4] induced by the incident light of 262 nm wave-
length. Formation of the 18 psec flat-top laser pulse
is an initial process [6]. Then the laser light is trans-
mitted from the laser table to the tunnel through a
22 m optical line and enters the vacuum through the
input window. It is directed by the vacuum mirror to
the cathode. Just before the entrance to the vacuum
there is a beam splitter, which directs 2% of the light
to the laser beam diagnostics system.
Before the entrance to the laser beam diag-
nostics there is a beam limiting aperture, which
makes the laser spot fixed at the cathode. The
transverse displacement of the laser beam before
the aperture will result in the laser beam cen-
ter of gravity movement. This change is de-
tected then by the quadrant diode - one should ob-
serve the repartition of the quadrant diode signals.
Fig.1. Optical scheme of the laser beam stability
diagnostics
The measurement system scheme is shown in
Fig.1. The quartz beam divider plates are inserted
before the detectors in order to match the input in-
tensity range and the linear response range of the
devices. CCD matrix chip is situated the way, that
optical path for the laser radiation is the same as
the path to the cathode. The camera is used for
the transverse laser beam profile measurements. The
quadrant diode is used for the laser beam pointing
position monitoring - the software analyses the trans-
verse profile together with the quadrant diode signals
and calculates the laser beam position. Photomultim-
plier (PM) is involved in the laser beam intensity
measurements. There is a possibility to reduce the
light intensity on the photomultiplier to measure PM
response function parameters using single photoelec-
tron method.
3. INTENSITY MEASUREMENTS
The structure of the pulse train defines that the
response time should be much less than 1 µsec, and
there is a 104 dynamical range to cover. That is
why photomultiplier (PM) was chosen for the inten-
sity measurements. Moreover it was not suggested
to use some special features of reconfiguration of the
field defining divider circuits, that is why complete
∗E-mail address: yevgeniy.ivanisenko@desy.de
166 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2007, N5.
Series: Nuclear Physics Investigations (48), p.166-170.
PM module H6780 (Hamamatsu) with intrinsic high-
voltage converter was chosen.
This PM module has a bialkali type cathode with
quantum efficiency of 0.8 % at 260 nm and an effective
area diameter of 8 mm. Another UV-sensitive type
H6780-03 has quantum efficiency ≈ 4.5%. The high-
voltage converter should have +12V of power supply.
The gain of the PM can be regulated externally in
range from 100 to 106. Maximal linear mode output
current is 100 µA. The cathode saturation current is
0.1 µA for the bialkali. If the gain is less then 103 the
linear output is limited by the cathode saturation,
otherwise by the space charge forces in the dynode
system during the multiplication.
To analyze the PM response function and noise
level a single photoelectron measurement was done.
The idea of the single photoelectron method of PM
characterization lies in measuring the response of PM
to light levels near to the one-electron creation level.
As far as the light source, such as LED, produces
number of photons in a pulse distributed by Pois-
son law, one can lower the intensity to suppress the
probability of two and more photoelectrons events,
but still have single photoelectrons. It means that
the probability of zero will be much higher and it
leads to a significant statistics of the noise events.
A good PM should easily resolve the single photo-
electron signal level. Let’s consider, that this signal
value is distributed by the Gauss law. Then it is de-
fined with two parameters: mean output charge Q1,
standard deviation of the distribution σ1 as a width
parameter. Then a probability to have charge x at
the cathode caused by one photoelectron event is for-
mulated [3]:
G1(x) =
1
σ1
√
2π
· exp
(
− (x−Q1)
2
2 · σ2
1
)
. (1)
Finally total PMT response is expressed by a
sum of different photoelectron quantity responses
weighted by the possibility of occuring Cn.
R =
∞∑
n=1
Cn · exp
(−(x− n ·Q1)2
2 · n · σ2
1
)
. (2)
On the Fig.2 there is a thin high peak, that corre-
sponds to ”zero” events distribution. On the left side
there is obviously the assymetric distribution and it is
clearly separated from the zero-distribution. It is not
Gaussian, because of more probability of low charge
noise events. One of them is autoemission from the
last dynodes. It can be seen comparing zero peak
of high voltage supplied not illuminated PMT and
much lower voltage supplied without illumination.
The zero-peak of the first one has a “tail”.
Result analysis is shown in Fig.2. For the PM
gain 2 · 106 the mean response signal is ≈ 21mV and
the standard deviation is 10 mV.
Due to the adjustable gain it is possible to
cover interesting intensity range with the linear re-
sponse of the PM. It is important for the cor-
rect definition of the intensity variations. One
should remember that internal PM noise level also
depends on gain. Gain change should be ac-
companied by the noise distribution measurement.
Fig.2. Single photoelectron spectrum
4. POINTING POSITION
MEASUREMENTS
Light beam position measurement devices are
based on position sensitive PM or position sensitive
photodiodes. For PM method one exchanges the an-
ode by two perpendicular non electrically contacted
wire arrays, which create a grid, and the current is
measured for each wire. The position of the light
beam center of gravity is obtained. Position sensitive
photodiodes have additional uniform resistive layer,
two side electrodes connected to the p-layer (one di-
mension) and the central point electrode connected
to the n-layer.
The current passing the resistance layer depends
on the distance to the electrode. If one can measure
two currents independently then the position of the
gravity center is obtained.
The first one is expensive and the second one is
not fast enough to measure position of each pulse at
1MHz repetitional rate. There is also charge coupled
discrete elements detector which is used for the trans-
verse laser beam intensity distribution measurements.
It is not sensitive and fast enough, to satisfy demands
for parallel to facility operation measurements.
There are two examples when fast controlling of
the incident light beam position is required: auto-
matic alignment of the laser beam lines [5], the po-
sition detectors for wavefront sensors of adaptive op-
tics. Both of them use a quadrant diode application.
The quadrant diode is essentially a usual photodiode
split into four quadrants, output current of each is
measured. Since the current is proportional to the
incident energy one can easily do alignment or mea-
sure cylinder-symmetric beam spot, if the dimensions
of the spot are smaller than the detector.
The idea of the hybrid detector was proposed for
the first time and the equipment was developed for
PITZ. The main thing, that differs this approach
from the laser beam auto-alignment or adaptive op-
tics wave front detectors, is taking into account the
167
transverse laser beam intensity distribution. The dis-
tribution is measured by the CCD matrix. From the
distribution it is possible to find relation between the
geometric center and the gravity center of the laser
beam, which is measured by the quadrant diode. In
such method there is no demand on the laser beam
transverse profile cylindric symmetry. The cathode
laser beam at PITZ should have a flat-top transverse
intensity distribution, which can be distort enough
on practice (Fig.3).
Fig.3. An example of the laser beam transverse intensity distribution
For the measurements in our case the PIN quad-
rant photodiode S4349 (Hamamatsu) was chosen.
The response time is ≈ 100 ns. The QD has 40%
quantum efficiency at 262 nm. Four signals are trans-
mitted to the electronics racks room, integrated, dig-
itized and stored at a hard drive. The sensitive area
is a square with 3 mm side. The gap between the
quadrants is 0.1 mm. Separating gaps of the CCD
matrix are parallel or perpendicular to the gap lines,
which divides the quadrant photodiode on four parts.
For the position measurements it is important to have
symmetry of the four channels of the quadrant diode.
If the condition is not matched at the level of the
equipment then it can be corrected by the analysing
software. To check this a test was made for indentity
of the quads and their electronic circuits. The inte-
grator channels after the test and the recalibration(is
done in the analysis software) are found to be with
the accuracy of 1%. Test of the quads showed equal-
ity with the same accuracy as the previous test, what
means if difference exist it is much smaller than the
value of 1%.
Linear response of the quadrants are limited by
the electronic interference at low intensities and by
the saturation at high intensities. That is why it was
decided to make a switchable quartz to mirror reflec-
tor before the quadrant diode. The mirror reflects
ten times more light than the quartz plate does.
Each quadrant integrates the light signal over its
surface. The same is done in the software for the
four parts of the spatial intensity distribution, which
is divided by the virtual gap cross. The cross can
be moved with the resolution of 8.3 µm - the dimen-
sion of the square pixel of the CCD. The quadrant
diode signals are simulated by the software and com-
pared with the normalized real ones. The position of
the cross relatively to the intensity distribution corre-
sponds to the minimal discrepancy between the real
and simulated values, defined as:
X =
S1 + S2
S1 + S2 + S3 + S4
, (3)
Y =
S1 + S4
S1 + S2 + S3 + S4
, (4)
where X and Y are independent and define the po-
sition on the surface. Si - is a signal from the ith
quadrant. Quadrants are numbered clockwise.
5. LASER BEAM TRANSVERSE PROFILE
MEASUREMENTS
The algorithm of the quadrant diode signals analy-
sis involves a transverse laser beam intensity distri-
bution, which is measured by the camera (Jai CV-
M10CX). The active area is 575x767 pixels, pixel di-
mensions is (8.3 x 8.3) µm. The minimal exposition
is 1/917000 sec. The camera is surrounded by the
lead wall to avoid bremsstrahlung illumination of the
semiconductor electronics of the camera. All of the
pixels are supposed to have equal quantum efficiency
and have noise level much smaller than the signal.
6. RESULTS
The single photoelectron measurements were done
and found, that for the gain of 2 · 104 and the aver-
age signal of 100 photoelectrons (10 mV) the response
function standard deviation equals 1 mV. For the case
of performed measurements one obtained standard
deviation of the signal 2.4 mV - the convoluted distri-
bution standard deviation of the intensity variations,
noises and PM response function. the deconvolution
gives in average 14 ± 1% standard deviation of the
168
intensity variation distribution (Fig.4), what will be
treated as an intensity stability characteristic.
The pointing position measurements results are
presented in Fig.5. Each pulse position in the 800
pulse train is averaged over 300 trains. Standard de-
viation of a laser beam pulse positions distribution
is regarded as a pointing position stability charac-
teristic and equals 18 ±1.3µm for the measurement.
The observed position change (drift) during the train
(Fig.5) presents also in the measurements made with
the CCD matrix. It is thought the position drift is
connected to the laser elements heating - the drift
corresponds to the pointing angle devation inside the
laser system of about 10−5 rad. That is a topic for the
laser development at the moment. Inspite of the cam-
era short enough exposition for capturing any laser
pulse from the train, it was not possible to determine
the drift in series of the different pulse positions dur-
ing the train, because the type of camera has films
covering active area, which excited by the ultraviolet
give afterglowing. This effect is called shadowing.
Fig.4. Averaged over 300 trains pulse intensities
(800 pulses train)
Fig.5. Averaged over 300 trains pulse positions (800 pulses train): along the X axis, along the Y axis and
the quadrant diode signals
For the emittance measurements up to 100 pulse
trains are used. If the bunch center of gravity is
floating from pulse to pulse during the measurement,
it causes the error of the size determination. AS-
TRA simulation software was used to find out how
the electron beam size and position on the cathode is
projected by the system into the screens. The soft-
ware tracks the initial particle distribution through
the user-defined electro-magnetic field configuration.
7. CONCLUSIONS
The system is fully implemented and ready to be-
come a tool for the facility investigations. The inten-
sity measurements have shown the laser beam inten-
sity stability at level of 14%. This will be a subject
for the laser system development. In the pointing
position measurements one has obtained position jit-
ter, position stability characteristic, of 18 µm. The
jitter and drift cause less than 1% error in electron
beam emittance measurements. It was shown in AS-
TRA simulations for the current electron beam line
configuration of PITZ facility.
Before there were two widely spread approxima-
tionsof the measured beam profile: gaussian or uni-
form distribution. Actually any cylindrically sym-
metric beam position could be measured with the
quadrant diode only. It is the first system to de-
termine the position of the light beam with arbitrary
transverse intensity distribution. Mostly the error of
the new hybrid position detector comes from the dis-
crete matrix element (camera), which measures the
profile.
8. ACKNOWLEDGEMENTS
I wish to thank following individuals for the
fruitful discussions, which have advanced the topic
and formed the final results: Juergen Baehr, Oleg
Kalekin, Sergey Khodyachykh, Sergey Korepanov,
Mikhail Krasilnikov, Sven Lederer, Anna Oppelt,
Lazar Staykov, Frank Stephan.
The work has been done with partial finance sup-
port of the European Community, contracts RII3-
CT-2004-506008 AND 011935, and Helmholz Assosi-
ation, contract VH-FZ-005.
169
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2. A. Oppelt et al., Status of the PITZ Facility
Upgrade // LINAC Conference, MOP020, USA,
Knoxville (TN), August 21− 25, 2006.
3. E.H. Bellamy, I. Chirikov-Zorin, S. Tokar et al.
Absolute Calibration and Monitoring of a Spec-
trometric Channel Using a Photomultiplier //
Nucl. Instr. and Meth. 1994, A339, p.468-476.
4. R.A. Loch. Cesium-Telluride and Magnesium for
high quality photocathodes // Masterdiploma
thesis. University of Twente, 2005.
5. A. Dunster et al. Automatic Alighnment Sys-
tem Testing for Vulcan // Central Laser Facility
Annual Report 2004/2005. CCLRC Rutherford
Appleton LAboratory, Chilton, Didcot, Oxon.,
0X11, 0QX, UK.
6. I. Will, G. Koss, I. Templin. The upgraded photo-
cathode laser of the Tesla Facility // Nucl. Instr.
and Meth. 2005, 541, p.467-477.
СИСТЕМА НЕПРЕРЫВНОГО МОНИТОРИРОВАНИЯ СТАБИЛЬНОСТИ
ИНТЕНСИВНОСТИ И ПОЛОЖЕНИЯ ПУЧКА КАТОДНОГО ЛАЗЕРА
ФОТОИНЖЕКТОРА
Е.Е. Иванисенко
Рассмотрена система, созданная для мониторинга стабильности положения и интенсивности им-
пульсов излучения лазерной системы фотоинжектора PITZ. Измерения осуществляются с использова-
нием трех детекторов: фотоэлектронного умножителя, квадрантного фотодиода и ПЗС камеры. Основ-
ное внимание уделено работе установки в номинальном режиме: 800 лазерных импульсов (длительность
20 пс) с частотой повторения 1 МГц, энергия в одном импульсе до 30 мкДж, частота последователь-
ностей 10 Гц.
СИСТЕМА БЕЗПЕРЕРВНОГО МОНIТОРИНГУ СТАБIЛЬНОСТI IНТЕНСИВНОСТI
ТА ПОЗИЦIЇ ПУЧКА КАТОДНОГО ЛАЗЕРА ФОТОIНЖЕКТОРА
Є.Є. Iванiсенко
Описана система безперервного мониторингу стабiльностi iнтенсивностi та позицiї катодного лазера
фотоiнжектора на установцi випробування фотоiнжекторiв у Цойтенi, DESY. Вимiрювання здiйсню-
ються фотоелектронним помножувачем, квадрантним фотодiодом та ПЗС. Вимiрювання проводилися
при нормальному режимi: 800 лазерних iмпульсiв тривалiстю 20 пс з частотою слiдування 1 МГц,
енергiя кожного iмпульсу до 30 мкДж, частота цугiв 10 Гц.
170
|
| id | nasplib_isofts_kiev_ua-123456789-110562 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T17:10:38Z |
| publishDate | 2007 |
| publisher | Німецький Електронний-Синхротрон (DESY) Німеччини |
| record_format | dspace |
| spelling | Ivanisenko, Y.Y. 2017-01-04T19:33:14Z 2017-01-04T19:33:14Z 2007 Photoinjector laser intensity and pointing position monitoring system / Y.Y. Ivanisenko// Вопросы атомной науки и техники. — 2007. — № 5. — С. 166-170. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 07.60.-j, 42.79.-e https://nasplib.isofts.kiev.ua/handle/123456789/110562 This work contains the description of a laser intensity and a laser beam pointing stability monitoring system, which was created for the Photo Injector Test Facility at Zeuthen, PITZ. The measurements are based on the usage of three detectors: a photomultiplier tube, a quadrant diode, and a coupled charge camera. Investigations were done for the nominal operation conditions: up to 800 laser pulses ( 20 psec duration) with a repetition rate of 1 MHz, a pulse energy of up to 30 microJ (wave length 262 nm), and a pulse train repetition rate is 10 Hz. Описана система безперервного мониторингу стабільності інтенсивності та позиції катодного лазера фото-інжектора на установці випробування фото інжекторів у Цойтені, DESY. Вимірювання здійснюються фотоелектронним помножувачем, квадрантним фотодіодм та ПЗС. Вимірювання проводилися при нормальному режемі: 800 лазерних імпульсів тривалістю 20 пс з частотою слідуванния 1 МГц, энергія кожного импульсу до 30 мкДж, частота цугів 10 Гц. Рассмотрена система, созданная для мониторинга стабильности положения и интенсивности импульсов излучения лазерной системы фото-инжектора PITZ. Измерения осуществляются с использованием трех детекторов: фотоэлектронного умножителя, квадрантного фотодиода и ПЗС камеры. Основное внимание уделено работе установки в номинальном режиме: 800 лазерных импульсов (длительность 20 пс с частотой повторения 1 МГц, энергия в одном импульсе до 30 мкДж, частота последовательностей 10 Гц. I wish to thank following individuals for the fruitful discussions, which have advanced the topic and formed the final results: Juergen Baehr, Oleg Kalekin, Sergey Khodyachykh, Sergey Korepanov, Mikhail Krasilnikov, Sven Lederer, Anna Oppelt, Lazar Staykov, Frank Stephan. 
 The work has been done with partial finance support of the European Community, contracts RII3-CT-2004-506008 AND 011935, and Helmholz Assosiation, contract VH-FZ-005. en Німецький Електронний-Синхротрон (DESY) Німеччини Вопросы атомной науки и техники Теория и техника ускорения частиц Photoinjector laser intensity and pointing position monitoring system Система безперервного моніторингу стабільності інтенсивності та позиції пучка катодного лазера фото-інжектора Система непрерывного мониторирования стабильности интенсивности и положения пучка катодного лазера фото-инжектора Article published earlier |
| spellingShingle | Photoinjector laser intensity and pointing position monitoring system Ivanisenko, Y.Y. Теория и техника ускорения частиц |
| title | Photoinjector laser intensity and pointing position monitoring system |
| title_alt | Система безперервного моніторингу стабільності інтенсивності та позиції пучка катодного лазера фото-інжектора Система непрерывного мониторирования стабильности интенсивности и положения пучка катодного лазера фото-инжектора |
| title_full | Photoinjector laser intensity and pointing position monitoring system |
| title_fullStr | Photoinjector laser intensity and pointing position monitoring system |
| title_full_unstemmed | Photoinjector laser intensity and pointing position monitoring system |
| title_short | Photoinjector laser intensity and pointing position monitoring system |
| title_sort | photoinjector laser intensity and pointing position monitoring system |
| topic | Теория и техника ускорения частиц |
| topic_facet | Теория и техника ускорения частиц |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/110562 |
| work_keys_str_mv | AT ivanisenkoyy photoinjectorlaserintensityandpointingpositionmonitoringsystem AT ivanisenkoyy sistemabezperervnogomonítoringustabílʹnostííntensivnostítapozicíípučkakatodnogolazerafotoínžektora AT ivanisenkoyy sistemanepreryvnogomonitorirovaniâstabilʹnostiintensivnostiipoloženiâpučkakatodnogolazerafotoinžektora |