Heavy ion beam pumped KrF* excimer laser [Elektronische Ressource] / von Aleksey Adonin

Aleks

Sujets

• Physik

Informations

• Publié par: goethe_universitat_frankfurt_am_main
• Publié le: 01 janvier 2008
• Nombre de lectures: 27
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Heavy Ion Beam Pumped
*KrF Excimer Laser





Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften





vorgelegt beim Fachbereich Physik
der Johann Wolfgang Goethe-Universität
in Frankfurt am Main





von
Aleksey Adonin
aus Sankt-Petersburg





Frankfurt 2007
D 30
















vom Fachbereich Physik der Johann Wolfgang Goethe-Universität
als Dissertation angenommen.










Dekan: Prof. Dr. Wolf Aßmus

Gutachter: Prof. Dr. Joachim Jacoby
PrivDoz. Dr. Andreas Ulrich
Datum der Disputation: 14. März 2008

Abstract
The high energy loss of heavy ions in matter as well as the small angular
scattering makes heavy ion beams an excellent tool to produce almost
cylindrical and homogeneously excited volumes in matter. This aspect can be
used to pump short wavelength lasers.
In an experiment performed at the GSI (Gesellschaft für Schwerionen-
forschung, Darmstadt, Germany) ion accelerator facility in December 2005 the
*well-known KrF excimer laser was pumped with an intense high energy
uranium beam. Pulses of an uranium beam with initial particle energy of
250 MeV per nucleon, provided by heavy-ion-synchrotron SIS-18, were
delivered to the HHT-target station and then stopped inside a gas laser cell.
9The maximum beam intensity reached in the experiment was 2,5·10 particles
Jper pulse, which resulted in 34 / specific energy deposited in the laser gas. g
By applying electron cooling and a bunch compression technique at SIS-18,
the beam pulses were compressed down to 110 ns (FWHM).
A mixture of an excimer laser premix gas (95,5% Kr + 0,5% F ) and a 2
buffer gas (Ar 4.8) was used as the laser gas in proportions of 35/65 and
60/40, respectively. The gas pressure inside the laser cell was varied in the
range of 1,2÷2 bar in continues flow mode. The experimental setup consisted
of a 1 m long stainless steel tube with a number of diagnostic viewports and
two mirror adjustment units. The optical cavity was formed by a flat, Al-
coated mirror at the beam entrance and a second dielectrically coated, highly
reflective mirror with 3 m radius of curvature at a distance of 1,3 m.
A beam of heavy ions has been used to pump a short wavelength gas laser
*for the first time. Laser effect on the KrF laser transition ( λ = 248 nm) has
been successfully demonstrated. Laser threshold for this specific setup was
9reached with a beam intensity of 1,2·10 particles per pulse. Laser action has
been clearly proofed by the following methods: appearance of the laser line,
spectral narrowing of the laser line, temporal narrowing of the laser signal,
non-linear response of the laser output intensity on the pumping power, and
cavity disalignment effect. An energy of the laser pulse of about 2 mJ was
9measured for an ion beam intensity of 2·10 particles per pulse. The time
delay of the onset of the laser emission with respect to the pumping pulse was
measured as a function of ion beam intensity. The dependence of spontaneous
emission spectra on the gas pressure in a range of 1,3÷2 bar was observed and
the optimal gas pressure for laser experiments in the sense of laser efficiency
was concluded.
As a next step in studying short wavelength lasers pumped with heavy ion
beams it is planned to reduce the laser wavelength down to the VUV region of
the spectrum, and to proceed to the excimer lasers of the pure rare gases:
* * * *Xe ( λ = 172 nm), Kr ( λ = 146 nm), Ar ( λ = 126 nm), Ne ( λ = 83 nm) 2 2 2 2
*and He ( λ = 80 nm). We believe that the use of heavy ion beams as a 2
pumping source may lead to new pumping schemes on the higher lying level
transitions and considerably shorter wavelengths (XUV and X-ray spectral
region), which rely on the high cross sections for multiple ionization of the
target species.

Contents
1. Introduction 1
1.1  Motivation of the work ..........................................................................................1 
1.2  Goals for the first experiment ........................................................3 
2. Theoretical Background 7
2.1  Interaction of heavy ion beams with matter ..........................................................7 
2.1.1  Stopping power in cold matter .....................................................8 
2.1.2  Calculation of “cold” stopping..................11 
2.1.3  Energy deposition by the ion beam............................................................12 
2.2  Rare gas halogen excimers ..................................................................................13 
2.2.1  Electronic structure and binding parameters......................14 
2.2.2  Spectroscopy and radiative parameters.......................................15 
2.2.3  Formation and quenching...........................................................................18 
3. Design of the Experiment and Numerical Predictions 27
3.1  Selection of the ion beam parameters..................................................................27 
3.2  Ion beam envelope calculation ............................................................................28 
3.3  Selection of an entrance window to the laser cell................................................31 
3.4  Ion beam stopping in the gas mixture...........................................33 
3.5  Energy deposition in the entrance mirror ............................................................40 
3.6  Calculation of the laser spot sizes........................................................................41 
3.7  Optical gain calculations......................................................................................42 
3.8  Conclusions..................................................................................46 
4. Experimental Setup and Diagnostics 47
4.1  GSI accelerator facility ........................................................................................47 
4.2  Setup of the optical cavity ...................................................................................50 4.2.1  Vacuum System..........................................................................................51 
4.2.2  High Pressure Gas System .........................................................................52 
4.2.3  Opto-Mechanical System of the Laser Cavity ..................53 
4.2.4  Pressure and Diagnostic Windows.............................................................53 
4.3  Diagnostic tools ...................................................................................................54 
4.3.1  Ion beam diagnostics.................................54 
4.3.2  Spectral measurements..............................60 
4.3.3  Laser and spontaneous emission measurements ........................................61 
4.3.4  Remote adjustment of cavity mirrors.........................................................63 
5. Experiment and Results 65
5.1  Ion beam and target parameters...........................................................................65 
5.2  Calculation of the ion beam sizes at the cavity entrance .....................................67 
5.3  Ion beam diagnosing with CCD-cameras ............................................................69 
5.3.1  Ion energy at cavity entry...........................................................................69 
5.3.2  Ion beam spot size..............................................................69 
5.4  Spectrometer data ................................................................................................72 
6.3.1  Demonstration of the laser effect .......................................72 
6.3.2  Spectral narrowing of the laser line.............74 
6.3.3  Dependence of spontaneous emission on gas pressure ..............................75 
5.5  Measurements with photodiodes .........................................................................77 
6.4.1  Light output from the ion beam intensity...................................................78 
6.4.2  Temporal narrowing of the laser emission.................................................80 
6.4.3  Time delays of the laser emission ..............................................................83 
6.4.4  Calculation of the laser output power........83 
5.6  Calculations of the Laser efficiency from the Threshold value..........................84 
6.5.1  Laser threshold value .................................................................................85 
6.5.2  Threshold conditions........................................................