Document 7212047

Transcript Document 7212047

Light related activities at High resolution and light source technology laboratory, Institute of Atomic Physics and Spectroscopy, Riga

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Institute of Atomic Physics and Spectroscopy

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Laboratory is a part of the Institute of Atomic Physics and Spectroscopy

Members  Dr. Atis Skudra (head)      Dr. Imants Bersons Dr. Gita Rēvalde Eng. Juris Siliņš PhD students: Nataļja Zorina,    Egils Bogans, Zanda Gavare, Mr.

Mārtiņš Bērziņš Collaboration partners:  Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia  CPAT, Toulouse, France  Institute of Non-thermal plasma physics, Greifswald, Germany  University of St.Petersburg, Russia  Tomsk State University, Russia  University of Mainz, Germany  Moscow Kurchatov’s Institute, Russia G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Research fields

              Low-pressure discharge plasma studies, mainly, inductive/capacitatively coupled; High frequency electrodeless discharge lamp technology and manufacturing Plasma/wall interaction Working life studies Radiation stability High-resolution emission spectroscopy, time and spatially resolved Spectral line shapes (resolution approx. 0.05 cm -1 ) (VUV-IR) Spectral line intensities - absolute and relative (VUV-IR) in dependence on working conditions, pressure etc Ion trap spectroscopy Atomic absorption spectroscopy Zeeman spectroscopy Daylight measurements Mercury concentration detection in the environment Theoretical studies of the Ridberg atom interaction with half-cycle pulses G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Atomic absorption and self absorption method

Unit volume Plasma source  The light from the unit volume can be absorbed by the rest of the plasma source  One can obtain the optical density by changing the length of the plasma source     0  (  )  1  

  (  (  ) )

l d

 G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

1. Method using a mirror

a mirror b Discharge vessel l 1 l 2 A





I b r

 

I b I b



I ab

 (

 1 ) 

I ab I b r A

– the “relative absorption”

I a

I b

– the intensity of the plasma sources

and

b r

– the reflection coefficient of the mirror

l 1 , l 2

and

– the lengths of the plasma sources

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

2. Method using a spectral light source  The precision of the method can be improved by placing the line spectra light source instead of the mirror.



I L



I P



I L



P I L I A

– the “relative absorption”

– the intensity of the lamp (plasma is off)

I P

– the intensity of the plasma (lamp is off)

I L+P

– the intensity of the plasma and lamp G.Revalde, ASI  In this experimental work the high-frequency electrodeless discharge lamp (HFEDL) have been used COST Action 529, Mierlo, 31.03.06-2.04.06

N i / (2J+1), cm -3 10 10

Determined concentrations for level s

5 Level s 5 , lamp Level s 5 , mirror

using both methods

p = 0.5 mbar, P = 2.26 kW Gas flow: 200 sccm Ar/ H2 mixture (Ar % 10..100%) Ar I 10 9 13,57 12,95 p 1 p 5 p p 7 9 p 10 12,34 p 2 4 p p 6 8 10 8 11,72 s 2 s 3 s s 4 5 0,00 10 7 0 20 G.Revalde, ASI 40 60 Ar % 80 100  The concentrations for the metastable level s 5 determined with two methods COST Action 529, coincide within the experimental error.

Mierlo, 31.03.06-2.04.06

Hg/Ar low pressure inductive coupled plasmas

3000 2500 2000 1500 1000 500

253.7nm

30 40 50 60

Cold spot temperature, grad C

70 G.Revalde, ASI

N. Denisova , G.Revalde, A. Skudra, G.Zissis, High-frequency electrodeless lamps in an argon-mercury mixture, J.Phys.D.Appl.Phys. 38, 2005, 3275-3284.

The intensity of the resonance line 253.7nm versus the cold spot temperature. Dashed line – numerical calculation, points – experimental data..

P Ar

 2

Torr

0  0 .

COST Action 529, Mierlo, 31.03.06-2.04.06

Electrodeless discharge lamps

 Bright radiators in the broad spectral range (VUV - IR);  Filled with gas or metal vapor+buffer gas like Sn, Cd, Hg, Zn, Pb, As, Sb, Bi, Fe, Tl, In, Se, Te, Rb, Cs, I 2 , H 2 , He, Ne, Ar, Kr, Xe, Dy,Tu(first samples) as well as combined Hg-Cd, Hg-Zn, Hg Cd-Zn, Se-Te etc (also isotope fillings, as example Hg 202 ) etc.

 No electrodes – long working life  Inductive coupled/ capacitatively coupled;  Hf, Rf Electromagnetic field excitation;  Different designs and types in dependence on application 4000 3000 2000 1000 Hg 0 200 300 400 500 600 Wavelength, nm 700 800 G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Line shape studies

Spectral line shape measurements and modelling, to control self absorption and to get important plasma parameters (such as gas temperature, lower state density, etc) Computer Amplifier Photomultiplier Lens Vacuum chamber Fabry – Perrot interferometer Lens Lamp Zeeman spectrometer G.Revalde, ASI Capillary Monochromator Power supply Capillary COST Action 529, Mierlo, 31.03.06-2.04.06

Theoretical approach

 Observed spectral line profile:    

``(   where 

(x) f ’(x)

- real profile,

f’’(x)

instrumental function

- function characterizing random errors

2 methods to find the real spectral line shape:   Line shape modeling unknown parameters – non-linear multi-parameter fitting of the model profile to an experimental spectral line profile by varying Solving the inverse task using Tikhonov’s regularization method

(1)

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Modelling

      Model includes the basic factors causing the spectral line broadening in HF discharge: Doppler, natural, collision.. These effects are accounted by means of the Voigt profile. Multiple overlapping lines are generated including hyperfine splitting and isotope shifts. Self-absorption (one beam approximation) The resulting profile is a convolution of the manifold of self-absorbed profiles and the instrument function. The resulting profile is fitted to the experimental lines by means of a non-linear multi-parameter fitting procedure.

Typically the following parameters are fitted: atom temperature, collisional broadening, optical density, light source inhomogenity, width of the instrument function.

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Solving the inverse problem by Tikhonov ´s method

To determine the real spectral line profile I(v) it is necessary to solve the inverse problem (1). The problem (1) is known as the classic Rayleigh reduction problem and can be described by the first kind of Fredholm integral equation:

b a





 ' 

c d

, (2) where

 '  - the kernel of the integral - the known instrument function;

- the distribution function, which was registered by apparatus;

- the unknown real profile a,b – the limits of the real profile; c,d – the limits of the measured (experimental) profile. G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

W e implemented the Tikhonov’s regularization method in our computations of Eq. (2). This method is based on a transformation of the initial problem to a problem of minimising the smoothing functional. The solution is the function that minimises the smooth ing functional (the Tikhonov’s functional):

 

d c

 

b a A

 '

' 

   2

  , where Ω – the stabilising functional:  

b a



2  

' , λ>0 – the regularisation’s parameter; The instrumental function has to be known. The reduction to ideal spectral device was performed in two stages: 1) the problem of the m inimum searching of the Tikhonov’s functional was solved. So we have got a regularized solution of the linear equations system depending on the regularis ation’s parameter

λ.

2) In the second phase the parameter of the regularization

λ.

was determined. G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Mercury 185 and 254 nm line examples

in dependence on the T cold spot (0 o C-100 o C)

Modelling

Ar/Hg 202 (99.8 %) 253,7 nm line

1,0 Hg202+Ar

Experimental Theoretical Real

0,8 253.7 nm, i=160 mA, without cooling 0,6

1,0

Hg202 - 90% +Ar (2 Torr) 253.7 nm, i=140 mA

without thermostabilisation 0,8 0,6 0,4

0,4

0,2

0,2

0,0

0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 Wavenumber, cm -1 0,7 0,8 0,9 1,0

0,0 0,2 0,4 0,6 0,8

Wavenumber, cm -1

1,0 Experimental Theoretical Real 1,2 Optical density 6.8

 dopl = 0,044 cm -1 (T=488 K) Reff= 0,84% 1,4 G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

185 nm resonance line

Reconstructed shapes i=200 mA G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

G.Revalde, ASI 10 8 6 4 2 0 0 12 14

Plasma/wall interaction

Working life studies 0,046 m g 0,46 m g 4,6 m g Hg 253.7 nm line intensity time dependance 50 100 150 Time, hours 200 250 COST Action 529, Mierlo, 31.03.06-2.04.06

Blackening of the walls of the vessel in the capillary lamp G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

12 nm z-range X, Y range 3 m m Images of the vessel surfaces obtained by AFM: a) without plasma treatment COST Action 529, Mierlo, 31.03.06-2.04.06

Regular daylight study – 3 years experience Relative daylight at 12:00 during 2004

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Spectral changes

Daylight in the winter and summer G.Revalde, ASI Wavelength, nm COST Action 529, Mierlo, 31.03.06-2.04.06

Mercury concentration detection in air in real time with 2 ng precision

•

Riga’s city example

G.Revalde, ASI GPS COST Action 529, Mierlo, 31.03.06-2.04.06

Mercury concentration measurements in the criminalistics

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06

Mercury rest in cartridge cases after the shot



0 



 

0 1 



 

0 2 G.Revalde, ASI Time after the shot COST Action 529, Mierlo, 31.03.06-2.04.06

G.Revalde, ASI COST Action 529, Mierlo, 31.03.06-2.04.06