Analysis of diode lasers by nearfield scanning optical ... - brighter.eu

WWW.BRIGHTER.EU Tutorial 

Breaking the diffraction limit: Analysis of 

diode lasers by nearfield scanning 

optical microscopy (NSOM) 

Jens W. Tomm a and Christoph Lienau b 

a 

b 

MaxBornInstitut für Nichtlineare Optik und Kurzzeitspektroskopie 

Berlin, MaxBornStr. 2 A, D12489 Berlin, Germany 

Institut für Physik, Fk. V, Carl von Ossietzky Universität Oldenburg 

Ammerländer Heerstraße 114118, D26129 Oldenburg, Germany 

christoph.lienau@unioldenburg.de 

WWW.BRIGHTER.EU Plenary Meeting at Tyndall, Cork 2008 

1

Outline 

1. Introduction 

NSOM = Nearfield Scanning Optical Microscopy 

Principles and opportunities 

Spatial resolution 

2. Methodology 

Laser emission, spontaneous emission and PL 

3. NOBIC = Nearfield Optical Beam Induced Current 

4. Experimental setups and equipment 

5. Analysis of waveguides and determination of mode profiles 

6. VCSEL 

7. Surface recombination velocity at facets 

8. Defect creation during device operation 

9. Summary 

10. Acknowledgement 


2

Introduction 

Nanostructures and Nanoanalytical Tools 

Optoelectronic devices 

Semiconductor Nanostructures 

10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm 

Farfield Optical Microscopy 

NearField NanoOptics 

... 


3

Introduction 

Scanning probe microscopy 

Compare: If 1 atom had the size of an orange, 

the cantilever would be 100 km long 

Disc players for atoms 


4

Introduction 

Space 

100 pm 

1 nm 

10 nm 

100 nm 

1 µm 

10 µm 

100 µm 

Nuclear Electronic motion motion 

in molecules in atoms + molecules 

Energy transport in 

polymers 

Electronic 

+ large biomolecules 

motion in 

semiconductor nanostructures 

Quantum transport 

Surface plasmon dynamics 

in metallic nanostructures 

1ns 

100ps 10ps 1ps 100fs 10fs 1fs Time 

Physical phenomena happen on ultrashort length and time scales 


5

Introduction 

Space 

100 pm 

1 nm 

Ultrafast nanooptics 

10 nm 

100 nm 

1 µm 

Electron microscopy 

Cathodoluminescence 

10 µm 

Ultrafast farfield 

100 µm optical microscopy 

Ultrafast nanoscale 

physics: Imaging tools 

1ns 

100ps 10ps 1ps 100fs 10fs 1fs Time 


6

Introduction 

Rayleigh limit: 

D x » 0.61 l / N.A. 

Sum 

Intensity 

Spot 1 

Spot 2 

The resolution in optical microscopy is limited 

by the wavelength of light 


7

Introduction 

Rayleigh limit: 

D x » 0.61 l / N.A. 

Sum 

Intensity 

Spot 1 

Spot 2 

The resolution in optical microscopy is limited 

by the wavelength of light 


8

Introduction 

Breaking the resolution limit in microscopy 

Nearfield scanning optical microscopy 

Diffractionunlimited resolution 


9

Introduction 

Spatial resolution in nearfield microscopy 

Electromagneticfield distribution: superposition of monochromatic plane waves: 

r r 

E = E exp( ik )exp(- 

i w t ) = E exp( ( i k x + k y )exp( ik z )exp(- 

i w t ) 

0 0 

0 

r 

k = k = k + k + k 

0 0 

for given k , k : two solutions: 

x 

y 

(a) propagating waves: 

(b) evanescent waves: 

2 2 2 

x y z 

x y z 

2 2 

k lat = k x + k y < k 0 

k z real . 

2 2 

k = k + k > k 

k z imaginary . 

lat x y 

Consequence: Intensity of evanescent waves decreases exponentially with increasing z 

0 

How to get optical superresolution ?: 

D k x D x ³ 1 

Use evanescent modes! 


10

Introduction 

Diffraction Diffraction by 1dimensinal by 1dimensional slit (Kirchhoff Approximation) 


11

Introduction 

Diffraction by 1Dimensional Slit (Kirchhoff Approximation) 

Diffraction by 1dimensinal slit (Kirchhoff Approximation) 

Monochromatic plane wave (k 0 

= 2pn r 

/l l = 800 nm) incident on slit (width d = 50 nm) 

1.0 

0 

Power Spectrum (a.u.) 

0.8 

0.6 

0.4 

0.2 

z =0 nm 

z = 10 nm 

z = 20 nm 

z = 40 nm 

z = 80 nm 

z = 160 nm 

l = 800 nm 

d = 50 nm 

n r 

= 3.4 

20 

40 

60 

80 

z Position (nm) 

0.0 

0 50 100 150 200 

Lateral Wavevector k lat 

(1/µm) 

100 

200 100 0 100 200 

Lateral Position (nm) 

Evanescent waves: k lat 

> k 0 

= 2pn r 

/l k z 

2 

= (k 0 

2 

k lat 

2 

) < 0 k z 

imaginary 

Propagating waves: k lat 

< k 0 

= 2pn r 

/l k z 

2 

= (k 0 

2 

k lat 

2 

) > 0 k z 

real 


12

Twodimensional 

field distribution E x 

(x,y) 

behind a r=30 nm aperture 

in a perfect metal film 

Introduction 

40 z = 0 nm 

|E x 

(x,y,z)/E 0 

| 

40 

20 

20 

0 0 

z = 1 nm 

20 

40 

20 

40 

40 

40 20 0 20 40 

z = 2 nm 

40 20 0 20 40 

40 z = 5 nm 

y (nm) 

20 

20 

0 0 

20 

20 

40 

40 

20 

0 

40 20 0 20 40 

40 z = 10 nm 

20 

40 

40 20 0 20 40 

40 z = 40 nm 

20 

0 

20 

40 

40 20 0 20 40 

x (nm) 

40 20 0 20 40 


13

Introduction 

Aperturebased nearfield microscopy 

+ excellent rejection of propagating waves 

low transmission efficiency (10 4 10 3 for 100 nm apertures) 


14

Introduction 

Aperturebased nearfield microscopy 


15

Introduction 

Nearfield Reflectance Spectroscopy 

with Uncoated Fiber Probes 

Illumination/Collection Mode 

Transmission efficiency close to 1 

Extremely high collection efficiency 

Sensitive probing of nearfield reflectance 

1.0 

Reflectance (a.u.) 

0.8 

0.6 

0.4 

0.2 

0.0 

1000 500 0 

Distance (nm) 

Resolution down to l/5 (150 nm) 

Experiment: F. Intonti et al, PRL 87, 076801 (2001), PRB 63, 075313 (2001) 

Theory: R. Müller and C. Lienau, Appl. Phys. Lett. 76, 3367 (2000). 


16

Pulse propagation 

through uncoated 

fiber probes 

2D modelling 

colorcode 

represents 

│E│ 2 A 0 

2 

R. Müller Appl. Phys. Lett. 76, 3367 

(2000) 

and J. Microscopy 202, 339 (2001). 

Introduction 

Propagation through Uncoated Fiber Probes 

Z(µm) 

2 

z exit 

0 

x | 2 /A 

|Ê 

6 

4 

2 

6 

4 

6 

4 

2 

1.0 

0.5 

0.0 

40fs 

52fs 

2 

2 1 0 1 2 

Y (µm) 

z = z exit 

260nm 

z = z exit 

+25nm 

285nm 

0 

2 1 0 1 

1 0 1 2 

Y (µm) 


17

Introduction 

Pulse propagation 

through metalcoated 

fiber probes 

R. Müller and C. 

Lienau 

Appl. Phys. Lett. 

76, 3367 (2000) 

J. Microscopy 202, 

339 (2001). 

Z(µm) 

2 

10 4 |Ê 

x | 2 /A 

0 

Power Density (norm.) 

Z exit 

2 

1 

1.0 

0.5 

0.0 

1.0 

0.5 

0.0 

(a) 

0 

0.50 0.25 0.00 0.25 0.50 

Y(µm) 

(b) 

2 

0 

x | 2 /A 

10 4 |Ê 

z =z exit 

z=z exit 

+25nm 

30 40 50 60 70 80 

Delay Time (fs) 

(c) 

4 

2 

0 

0.1 0.1 

Y (µm) 

10 

0.1 

0.001 

0.1 0.1 

Y (µm) 

720 760 800 840 880 

Wavelength(nm) 

2D modelling 

colorcode represents 

│E│ 2 A 0 

2 

│E│ 2 A 0 

2 

of a 

10 fs Gaussian pulse 

at the 100 nm aperture 

____ input pulse 

____ output pulse 


18

Introduction 

Application: Raman spectroscopy of Carbon Nanotubes 

A. Hartschuh et al., Phys. Rev. Lett. (2003) 


19

Introduction 

Nanophotoluminescence of single localized excitons 

T = 15 K 

500 nm 

1.0 

F. Intonti et al., Phys. Rev. Lett. 87, 076801 (2001). 

Intensity (a.u.) 

0.8 

0.6 

0.4 

0.2 

0.0 

790 792 794 796 798 800 

Wavelength (nm) 


20

Introduction 

Apertureless Nearfield Scanning Optical Microscopy 

+ Strong field enhancement (10 x) at ultrasharp metal tips 

+ Spatial resolution limited by radius of curvature of the tip 

+ Spatial resolution down to 10 nm (and beyond?) 


21

Outline 





2. Methodology, Laser emission, spontaneous emission and PL 




6. VCSEL 



9. Summary 



22

Analysis of laser emission 

RW laser 

~10 nm 1 µm 

2 µm 3 µm 4 µm 

5 µm 6 µm 7 µm 

W. D. Herzog, M. S. Ünlü, B. B. Goldberg, G. H. Rhodes, and C. Harder, Appl. Phys. Lett. 65 688 (1997). 


23


VCSEL 

Emission intensity (color) 

Van der Rhodes et al. 

Appl. Phys. Lett. 72,1811 (1998) 

VCSEL aperture (blue) 

I=7 mA I=10 mA I=15 mA 


24


Such work at devices is extremely useful, 

1. if confocal microscopy 

fails 

if not, you waste 

your resources 

2. if the fiber tip does not 

influence the emission 

unfortunately, this is the 

case when investigating 

lasing devices 

These statements hold in general for the 

application of NSOM ! 


25

What is better? 

Spontaneous emission 

Photoluminescence 

Absorption (Photocurrent) 

Substrate 

ARcoating 

cladding 

fiber tip 

lockin 

amplifier 

DQW 

waveguide 

cladding 

heat sink 

heat sink 


26




Absorption (Photocurrent) 

Substrate 

ARcoating 

cladding 

fiber tip 

lockin 

amplifier 

DQW 

waveguide 

cladding 

heat sink 

heat sink 


27




Absorption (Photocurrent) NOBIC 

Substrate 

ARcoating 

cladding 

fiber tip 

lockin 

amplifier 

DQW 

waveguide 

cladding 

heat sink 

heat sink 


28

NOBIC 

NOBIC = Nearfield Optical Beam Induced Current 

Buratto et al. (AT&T Bell Lab.) 

Appl. Phys. Lett. 65, 2654 (1994) 

Excitation at 633 nm 

(2 mW in, ~2 nW out) 

NOBIC 

NOBIC signal (a.u.) 

A 

B 


29

Outline 










6. VCSEL 



9. Summary 



30

Experimental setups and equipment 


31


Fibertip distance control 


32


Fibertip distance control 


33


Homebuilt Scanning Nearfield Optical Microscopes 

Setup with cryostat for 

Measurements at 10 300 Kelvin 

G. Behme et al., Rev. Sci. Instrum. 

68, 3458 (1997) 

"Customers:" 

Uni Magdeburg, D 

KTH Stockholm, Sweden 

Forschungszentrum Jülich, D 

University of Arkansas, USA 


34


NSOM data 

PCsignal (R) 

topography 


35

Outline 










6. VCSEL 



9. Summary 



36

PC 

Analysis of waveguides 

Lockin 

amplifier 

Lockin 

amplifier 

Setup 

Excitation laser 

Modulator 

(1.2 kHz) 

AR coating 

Heat sink 

LOC waveguide 

Substrate 

Cladding layer 

Double quantum well 


37


Results obtained at single symmetric and 

asymmetric waveguides 

Step INdex 

SIN 

Large Optical Cavity 

LOC symmetric waveguide 


LOC asymmetric waveguide 

potential 

potential 

potential 

0 1 2 3 4 5 

x (µm) 

0 1 2 3 4 5 

x (µm) 

0 1 2 3 4 5 

x (µm) 

resonant NSOM Photocurrent (Absorption) 


38


Step INdex 

SIN 





PC Signal (a.u.) 

2.0 

1.5 

1.0 

0.5 

0.0 

1 0 1 

Tip Position (µm) 


1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

1 0 1 



1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

1 0 1 


m=2 

m=2 

m=1 

m=1 

m=0 

m=0 

1 0 1 

Position (µm) 

1 0 1 


1 0 1 



39


Comparison of the guided modes in a waveguide 

and the wavefunctions in a quantum well 


40


Step INdex 

SIN 


2.5 

2.0 

1.5 

1.0 

0.5 




1.2 

1.0 

0.8 

0.6 

0.4 

0.2 




1.0 

0.5 

0.0 

1 0 1 


0.0 

1 0 1 


0.0 

1 0 1 


NSOM Photocurrent reveals mode structure of waveguides 

asymmetric waveguides have a specific NSOM Photocurrent signature 


41


NOBIC contrast from the photocurrent phase for nonresonant 

(surface) excitation 

NOBIC line scans from the symmetric 

LOC structure 

NOBIC line scans from the asymmetric 

LOC structure 

Absolute Value,F, and E 

g 

(a.u., °, and eV) 

2,5 

2,0 

1,5 

1,0 

0,5 

excitation photon 

energy: 2.8 eV 

absolute value 

phase 

Absolute value,F, and E 

g 

(a.u., °, and eV) 

3,0 

2,0 

1,0 

excitation photon 

energy: 2.8 eV 

absolute value 

phase 

(117+24) nm 

0,0 

2 1 0 1 2 

x (µm) 

0,0 

2 1 0 1 2 

x (µm) 


42


Single waveguides 

Resonant excitation (coupling into the 

waveguide modes) 

NOBIC reveals mode structure of waveguides 

asymmetric waveguides have a specific NOBIC 

signature 

Nonresonant excitation (pure carrierpair creation) 

detection of the QW within the waveguide 

T. Guenther et al. 

„NearField Photocurrent Imaging of the Optical Mode 

Profiles of Semiconductor Laser Diodes“ 

Appl. Phys. Lett. 78 14631465 (2001). 


43

‘regular’ highpower 

diode laser array 

Nanostack Ò 


Nanostacks Ò interband cascade diode laser 

Energy gap (eV) 

+ 

J. 

2.2 

n 

p 

2.0 

1.8 

1.6 

1.4 

2 0 2 4 6 8 10 

Local position in growth direction (µm) 

n 

p 

P. van der Ziel and W. T. Tsang, Appl. Phys. 

Lett. 41, 499501 (1982). 

J. Ch. Garcia, E. Rosencher, Ph. Collot, N. 

Laurent, J. L. Guyaux, B. Vinter, and J. Nagle, 

Appl. Phys. Lett. 71, 37523754 (1997). 

S. G. Patterson, G. S. Petrich, R. J. Ram, and L. A. 

Kolodziejski, Electron Lett. 35, 395 (1999). 

C. Hanke, L. Korte, B. D. Acklin, M. Behringer, G. 

Herrmann, J. Luft, B. De Odorico, M. Marchiano, J. 

Wilhelmi, Proc. SPIE 3947, 5057(2000). 

http://www.osramos.com/news/news_power.html 


44


Detailed analysis of Nanostacks 

Ò by NSOMbased 

spectroscopy 


Photocurrent (Absorption) 

Device emission 

x (µm) 

8 

7 

6 

5 

4 

3 

2 

1 

1 2 3 4 5 6 7 8 

y (µm) 


45

Results from NanostacksÒ with two vertically stacked 

asymmetric waveguides 

NSOM Device Emission 


1.0 

1.0 

Electroluminescence (a. u.) 

0.8 

0.6 

0.4 

0.2 

Laser signal (a.u.) 

0.8 

0.6 

0.4 

0.2 

0.0 

0.0 

0 2 4 6 8 10 

0 2 4 6 8 10 

x (µm) 

x (µm) 

Substrate 

duty cycle: 2x10 5 

no thermal load 


46


NSOM PL Emission 

1.00 

0.75 

1.0 

0.8 

11 µW 

160 nW 

16 nW 

PL signal (a. u.) 

0.50 

0.25 

PL signal (a. u.) 

0.6 

0.4 

0.2 

0.00 

0 2 4 6 8 10 

x (µm) 

excitation photon energy: 2.8 eV 

detection photon energy: 1.5 eV 

0.0 

0 2 4 6 8 10 

x (µm) 


detection photon energy: 1.5 eV 

PLsignal ~ dn 


47


resonant and nonresonant NSOM Photocurrent (Absorption) 

1.0 

1.0 

0.8 

0.8 

PC signal (a. u.) 

0.6 

0.4 

0.2 

PC Signal (a. u.) 

0.6 

0.4 

0.2 

0.0 

0 2 4 6 8 10 

x (µm) 

0.0 

0 2 4 6 8 10 

x (µm) 



Photocurrentsignal ~ dn´grad(V) 

V. Malyarchuk et al. "Uniformity tests of individual segments of interband 

cascade diode laser nanostacks Ò " J. Appl. Phys. 92, 27292733 (2002). 


48

NOBIC at VCSELS 

Photocurrent (a.u.) 

VCSEL emission energy 'barrier 

10 0 absorption' 

due to 

the Al 0.25 

Ga 0.75 

As 

barriers 

'defect region' 

'QW region' 

onset of the Braggmirror 

absorption at about 1.62 eV 

10 1 

10 2 

10 3 

10 4 

10 5 

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 

Photon energy (eV) 


49

Outline 










6. VCSEL 



9. Summary 



50

Surface Recombination Velocity 

v s 

Reflection PL experiment 

uncoated fiber tip 

spatial resolution: 150 nm 

L D 

51 

V. Malyarchuk, J. W. Tomm, V. Talalaev, Ch. Lienau, 

F. Rinner, and M. Baeumler Appl. Phys. Lett. 81 346 (2002). 

WWW.BRIGHTER.EU Plenary Meeting at Tyndall, Cork 2008


P = 10 µW P = 300 µW 

QW PL collected 

through the fiber 

and detected by 

a single photon 

counting system 

y (µm) 

2 

1 

0 

PL 

0 0.5 1.0 

1 0 1 2 3 

x (µm) 

y (µm) 

2 

1 

0 

PL 

0 0.5 1.0 

1 0 1 2 3 

x (µm) 

0.06 0 0.06 

DPL 

0.06 0 0.06 

DPL 

Lineleveled 

images 

y (µm) 

2 

1 

y (µm) 

2 

1 

0 

1 0 1 2 3 

x (µm) 

0 

1 0 1 2 3 

x (µm) 


52


1.0 

Signal (a.u.) 

0.5 

300 µW 

100 µW 

30 µW 

R 

0.0 

0.0 1.0 2.0 

x (µm) 


53


2 2 

n 

D( + ) n - + n g( x , y ) = 0 

L = 

D 

2 2 

x y t 

rec 

D t 

rec 

2 2 

0 y 0 y 

2 

( - x x ) + ( - ) 

- 

2 

1 

s 

g( 0 

x, 0 

y) 

= e 

2 ps 

x=0: 

n 

D = v s 

× n 

x = 

x 0 

a 

0 0 

diffusion length L D and the product 

(v × t ) can be deduced 

s 

rec 

PL (a.u.) 

1.0 

0.5 

0.0 

PL 

v s 

= 0.5 x 10 6 cm/s 

v s 

= 1.0 x 10 6 cm/s 

v s 

= 3.0 x 10 6 cm/s 

0.0 1.0 2.0 

x (µm) 

Example calculated for: 

D = 15 cm 2 /s t = 1.7 ns 


54


1.0 

Signal (a.u.) 

0.5 

L D 

300 µW 

100 µW 

30 µW 

R 

0.0 

v s *J 

0.0 1.0 2.0 

x (µm) 


55


3.0 

2.5 

Additional 2.5 ps 

PLexperiment 

provides t 

2.0 

L 

D (µm) 

2.0 

1.5 

1.5 

1.0 

QW (ns) 

t 

1.0 

0.5 

0.5 

0.0 

1 10 100 1000 

Power (µW) 


56


8.0 

30 

v 

s (10 6 cm/s) 

6.0 

4.0 

2.0 

20 

10 

D (cm 2 /s) 

0.0 

0 

1 10 100 1000 

Power (µW) 

V. Malyarchuk, J. W. Tomm, V. Talalaev, Ch. Lienau, F. Rinner, and M.Baeumler 

Appl. Phys. Lett. 81 346 (2002). 


57

Outline 










6. VCSEL 



9. Summary 



58

Defect creation during device operation 

Result from the BRIGHT project 

200 

180 

160 

Osram (BRIGHT) 51011+3 

2.5 

2.0 

10 4 PC FTIR Spectra 

Red LD OSRAM 510311 

10 3 

Power (mW) 

140 

120 

100 

80 

60 

40 

0h 

0.5h 

1.5h 

3h 

9h 

15h 

31h 

55h 

1.5 

1.0 

0.5 

Voltage (V) 

PC signal (a.u.) 

10 2 

10 1 

10 0 

10 1 

Before Aging 

9h Aging 

30h Aging 

55h Aging 

20 

10 2 

0 

0.0 0.2 0.4 0.6 0.8 

Current (A) 

0.0 

1.0 1.5 2.0 2.5 3.0 

Energy (eV) 


59


PC signal (a.u.) 

10 0 PC FTIR Spectra 

Red LD OSRAM 510311 

10 1 

Before Aging 

9h Aging 

30h Aging 

55h Aging 

DefecttoBand 

Transitions? 

At 1.7 eV (730 nm), there is 

a threefold increase of the 

signal within 55 h of aging. 

10 2 

Where are the 

‘defects’ located? 

1.0 1.2 1.4 1.6 1.8 

Energy (eV) 

Active region??? 


60


1. Laterally, i.e., where along the device… 

Osram (BRIGHT) 51011+3 

LBIC signal (a.u.) 

0.20 

0.15 

0.10 

0.05 

pristine device 

3h 

9h 

Front view of the laser structure 

substrate 

active region 

epilayer sequence 

0.00 

0.0 0.2 0.4 0.6 

y (mm) 

LBIC (Laser Beam Induced Current) excited resonantly to the defects reveals 

them to be underneath the metalized emitter stripe. 


61


2. Vertically, i.e., where along the layer sequence … 

Front view of the laser structure 

substrate 

aged area 

‘Pristine’ reference 

area 

~ 1.5 µm 


62


NOBICData: 

(Nearfield Optical Beam Induced Current) 

1000 nm 1000 nm 1000 nm 

633 nm 730 nm topography 

pristine device region 


63


1000 nm 1000 nm 1000 nm 

633 nm 730 nm topography 

aged device region 

Signal (a.u.) 

10 1 633 nm 

730 nm 

10 0 

10 1 

10 2 

aged region 

0.0 0.5 1.0 1.5 2.0 

x (µm) 


64


10 1 633 nm 

730 nm 

10 0 

10 1 633 nm 

730 nm 

10 0 

Signal (a.u.) 

10 1 

pristine region 

Signal (a.u.) 

10 1 

aged region 

10 2 

10 2 

0.0 0.5 1.0 1.5 2.0 

x (µm) 

0.0 0.5 1.0 1.5 2.0 

1.5 µm 1.5 µm 

x (µm) 

There is a threefold increase of the 730 nm signal with respect to the 633 nmsignal 

1.5 µm away from the active region (towards the heat sink), there is no photosensitivity. 

The creation of deep levels takes place at a location that allows interaction with the 

laser emission. 

There are additional 3 sets of data couples from different regions, which confirm the result. 

Claus Ropers et al. Appl. Phys. Lett. 88, 133513 (2006). 


65

Summary 




Methodology, Laser emission, spontaneous emission and PL 

NOBIC = Nearfield Optical Beam Induced Current 


Analysis of waveguides and determination of mode profiles 

VCSEL 

Surface recombination velocity at facets 


NSOM is extremely useful if you need a spatial resolution beyond the 

diffraction limit. 

NOBIC allows optical analysis at devices along growth direction. 


66

Acknowledgement 

• Christoph Lienau 

• Alexander Richter, Tobias Günther, Viktor Malyarchuk, 

Roland Müller, Claus Ropers, Thomas Elsässer 

• Martin Behringer, Johannes Luft, Peter Brick, Norbert 

Linder, Bernd Mayer, Martin Müller, Sönke Tautz, 

Wolfgang Schmid, Götz Erbert, Jürgen Sebastian, 

Siegfried Gramlich, Eberhard Richter, Heiko Kissel, Frank 

Brunner, Markus Weyers, Günter Tränkle 


67

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