Sodium laser system

High Power High-Repetition-Rate Microsecond
Pulse Sodium Beacon Laser for TMT
Bo Yong
Research Center for Laser Physics & Technology (Laser Center)
Technical Institute of Physics and Chemistry (TIPC)
Chinese Academy of Science (CAS)
03-11-2014
1
Outline
1. Introduction of Sodium Laser Guide Star (LGS)
2. Development of TIPC Sodium Laser System for TMT
3. Summary
2
1. Introduction of Sodium Laser Guide Star
It is very important for a telescope to achieve high image resolution.
However, light from any space object is greatly distorted by
atmospheric turbulence. It severely limits the image quality of large
ground-based telescopes as shown in the Fig.1.
These distortions can be corrected in real time by using adaptive
optics (AO). The image quality will be improved greatly by AO as
shown in the Fig.2.
Fig.1 without AO
Fig.2 with AO
For example,
Spatial resolution
could be increased
by 150 times for
30-m level
telescope with AO.
Image of the Galaxy center by Keck telescope
3
1. Introduction of Sodium Laser Guide Star
 A bright guide star is necessary in the AO system
The wavefront from a bright guide star close to the object is sensed
which used to correct the object’s wavefront aberration from the
atmospheric turbulence by a deformable mirror in the AO system .
 Natural guide star (NGS)
Sky coverage less than 1% because
of the distribution of bright stars.
Space objects
~100km
Sodium layer
 Sodium laser guide star (LGS)
Created by exciting atomic sodium
at its strong D2 line of 589.159nm in
the upper atmospheres (85-105km)
 High sky coverage (~100%)
 High altitude ( ~100km)
 High brightness (V~5)
--- Perfect for AO system
NGS
Sodium LGS
Wavefront
detector
atomospheric
turbulence
Deformable
Mirror
0km
Sodium laser
Telescope
CCD
4
1. Introduction of Sodium Laser Guide Star
 Sodium laser guide star is the brightest
Sodium layer measured at UBC
Atoms in the
upper
atmospheres
Wavelength
(nm)
Density
(cm-3 )
Cross section
( 10-12cm2 )
Density* Cross
section ( 10-9cm )
Na
589.159
5000
15
75
Fe
372.0
3000
1.0
3.0
Ca
422.7
100
38
3.8
5
1. Introduction of Sodium Laser Guide Star
 Multiple guide stars are used to increase the field of view (FOV)
 The atmospheric anisoplanatism
effect limits the FOV in SCAO
(Single Conjugate AO)
 The cone effect from sodium
LGS’s limited altitude decreases
off-axis AO performance
 Multi Conjugate AO (MCAO)
can increase the FOV to
more than 1 square arc min
Sodium
LGS asterism
MCAO tests on Gemini
Object
NGS
Object
NGS
105km
105km
Sodium layer
Sodium layer
80km
80km
Sodium
LGS
Sodium LGS
asterism
Ummeasured
turbulence
Unmeasured
turbulence
0
0
Telescope
Image with SCAO
Telescope
Image with MCAO
6
1. Introduction of Sodium Laser Guide Star
 Sodium lasers are key components of large ground based
telescopes to achieve high resolution in a big FOV currently.
Laser launch
telescope
UH 2.2m
VLT 8.2m
Beam
transfer
optics
Keck 10m
TMT 30m
TMT will be found in 2020
Sodium
laser
systems
TMT with its LGS facility (LGSF) design
7
1. Introduction of Sodium Laser Guide Star
 Laser System of TMT LGSF Requirements
 Sodium laser system
 Beam transfer optics
 Laser launch telescope
 Laser safety system
TMT LGS asterism
TIPC is developing the laser system for TMT
8
1. Introduction of Sodium Laser Guide Star
 Sodium Laser Specification Requirements
Sodium laser is used to generate a bright and compact guide star
 Brightness --- TMT requirement: the coupling efficiency with the
mesospheric sodium layer is at least 130 photons-m2/s/W/ion
 Compact --- TMT requirement: the LGS spot size is less than 1 arc sec
 Laser fundamental specifications
 Output power : > 25 W
 Wavelength : Na-D2a line
 Linewidth : < 1.2 GHz
FWHM
 Beam quality: ~1.2 DL
 Polarization: > 98%
Issues: How to generate high power &
high beam quality laser in the specific
wavelength with the narrow linewidth?
Na D2 spectrum
DL-Diffraction limitation
9
1. Introduction of Sodium Laser Guide Star
 Development status of sodium laser system
Lasers
Power in Lab (W)
Dye laser ns pulse operation
12W of LLNL
Diode
pumped
solid-state
laser
& fiber
laser
LGS (V)
9
Characteristics
Operate inconveniently,
difficult at high power
CW operation
5.1@40W High power, compact,
electric driving, high
• 50W Fiber Laser of Toptica 7.9@10W reliability, etc
s-pulse operation
• 50W SSL of Fasor
• 20W SSL of MIT/UC
8.1@10W
• 100W SSL of TIPC
6.5@25W
CW 40W in Fasor
CW 20W in Toptica
s-pulse 30W in TIPC10
1. Introduction of Sodium Laser Guide Star
 Advantage of a s-pulse sodium laser system
The SNR(Signal Noise Ratio) of the light wavefront is higher
because the s-pulse sodium LGS could be gated. 105km
 To eliminate the Rayleigh backscatter
effect and fratricide effect between the
multiple guidestars (Fig.1)
 To reduce LGS elongation when the
LLT at the side of the telescope (Fig.2)
Sodium
LGS
85km
Sodium LGS
images
Rayleigh
backscatter
Rayleigh
backscatter
Fig.1
Sodium
beacon
Fig.2
Rayleigh
backscatter
Launch telescope 11
1. Introduction of Sodium Laser Guide Star
 Advantage of a s-pulsed sodium laser system
Eliminate the Rayleigh backscatter noise by tracking the laser pulse signal.
The pulse width is 50-550s to reduce the sodium layer absorption saturation.
Transit time 1-2ms
Laser pulse
Photo return
Rayleigh return
Sodium return
Clear CCD frame
Integrate on WFS CCD
Read out WFS CCD
Scheduling of AO system operation
From Prof. Edward Kibblewhite
12
2. Development of TIPC sodium laser system
- 2006, TIPC began to develop the s-pulse sodium laser system
- 2009, output power of 13W in lab achieved, to cooperate with TMT
- 2010-2011, output power of 33W in lab achieved for the laser
prototype 1#, sodium LGS of V=8.2 generated in Lijiang site
- 2012-2013, output power of 53W in lab achieved for the laser
prototype 2#, sodium LGS of V=6.5@25W generated in Lijiang
site and 260-300 photons-m2/s/W/ion generated in UBC site
- 2014, output power of 102W in lab achieved, which is the highest
power in the world as reported.
33W in 2010
53W in 2012
102W in 2014
13
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
 It is difficult to find a spectrum line to generate
589nm by frequency-doubling solid-state laser
 Coincidentally, 589nm light can be achieved by
sum-frequency mixing 1064nm and 1319nm
Nd:YAG laser. However, it is difficult to
generate high power 1319nm laser for the
1319nm line is very weak.
Pump band
808nm
4
Upper level
R2
F3/2
R1
1319nm
1064nm
4
X6
X5
X4
X3
X2
I15/2
X1
4
I13/2
Lower level
Y6
Y5
Y4
Y3
4
I11/2
4
Nd:YAG fluorescence spectrum
I9/2
Y2
Y1
Ground
level
Nd:YAG spectrum 14
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
High power, high beam quality, narrow linewidth, exactly tunable
 Laser oscillator
It is difficult to generate high power 1064nm or 1319nm output with high
beam quality and narrow linewidth only by one oscillator
 high power→high gain→many longitudinal modes→linewidth expanding
 high power→much waste heat→beam quality decreasing
 MOPA – Master oscillator power amplifier
It is good method to generate high power 1064nm or 1319nm output with high beam
quality and narrow linewidth
 Seed laser：low power with high beam quality and narrow linewidth
 Power amplifier: to achieve high power, beam quality and linewidth
1064nm Nd:YAG MOPA Laser
1319nm Nd:YAG MOPA Laser
SFG＝>589nm output
15
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
 Schematic of the laser system
1319nm
seed laser
Beam
expander
Wavelength & temperature controller
1064nm
seed laser
Beam
expander
1319nm
Amplifier I
Beam
shaping
Beam
shaping
1319nm
Amplifier II
1064nm
Amplifier I
Beam
shaping
Beam
expander
Wavelength & temperature controller
Collector
Waveleng Feedback
589nm
Beam
EOM system
expander
Shutter
Beam
expander
Temperature controller
Beam
expander
SFG system
Beam
Combiner
 The seed laser is unidirectional ring oscillator to generate Watt-level TEM00
1064nm&1319nm beam with a narrow linewidth & high beam quality.
 The amplifier is used to achieve high power for 1064nm&1319nm laser.
 The 589nm light is obtained by extra-cavity sum-frequency mixing of
1064nm&1319nm laser with a nonlinear crystal.
16
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
 The 1064nm MOPA system
1064nm MOPA system
LH1
TP1
1064nm
Beam
Isolator
master-oscillator
forming
g
1064nm output
Specifications of 1064nm laser:
 Output power：80 W
 Beam quality：M2 ~ 1.6
 Linewidth：~ 0.2 GHz
 Wavelength tuning：48 GHz
 Polarization: > 99%
 Repetition rate: 600 Hz
 Pulse width: ~ 120 s
QR1
LH2 QW1
M1
Beam
forming
g
Rod module
 Diode-pumped module is used to achieved
uniform & high-power gain distribution
 Beam shaping optics is used to match the
gain medium
 Imaging relay optics is used to reduce the
Fresnel diffraction
 Synchronous controller is used to achieve
pulse synchronization between the 1064nm
laser seed pulse and the diode-pumped pulse
17
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
 The 1319nm MOPA system
1319nm MOPA system
1319nm
master-oscillator
Isolator
LH3
TP2
Beam
forming
g
Beam
forming
g
TP3
LH5
 Output power：62 W
 Beam quality：M2 ~ 1.8
 Linewidth：~ 0.4 GHz
 Wavelength tuning：24 GHz
 Repetition rate: 600 Hz
 Pulse width: ~ 100 s
LH4
QW2
M2
Beam
forming
g
Specifications of 1319nm laser:
 Polarization: > 99%
QR2
QR3
LH6
1319nm output
Slab module
 Diode-pumped module is used to achieved
uniform & high-power gain distribution
 Two amplifiers to increase the output power
 Beam shaping optics is used to match the
gain medium
 Imaging relay optics is used to reduce the
Fresnel diffraction
 Synchronous controller is used to achieve
pulse synchronization between the 1319nm
laser seed pulse and the diode-pumped pulse18
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
Numerical simulation
 The 589nm extra-cavity SFG system
The SFG can be described with three coupling wave equations
dA3
i3

 d eff A1 A2 e ikz
dz
Cn3 
Gaussian beam wz   w0
dA1
i1

 d eff A3 A2* e ikz
dz
Cn1 
dA2
i 2

 d eff A3 A1* e ikz
dz
Cn 2 
589nm
  
L 
M 2  1 
z



2
2
n

w

0 

2
Phase matching：k=0
The equations are solved by using the improved
Euler method
1064nm
1319nm
Nonlinear crystal
Schematic of SFG model
19
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
Beam parameters are optimized to achieve high SFG efficiency
O-O efficiency (%)
30
20
10
0
0.0
0.1
0.2
0.3
Beam waist (mm)
Optical-to-optical conversion efficiency Optical-to-optical conversion
as a function of 1064nm&1319nm power efficiency as a function of beam waist
30
O-O efficiency (%)
O-O efficiency (%)
30
20
10
0
0
10
20
30
Crystal length (mm)
40
50
25
20
15
0
1
2
3
4
1064nm output power vs 1319nm
Optical-to-optical conversion efficiency Optical-to-optical conversion efficiency as a
as a function of nonlinear crystal length function of 1064nm&1319nm power ratio20
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
 The 589nm extra-cavity SFG system
Beam
1064nm
 Output power : 53W@500Hz /
42W@600Hz / 32W@800Hz /
26W@1000Hz
 Wavelength : Na D2a line
 Linewidth : ~ 0.6 GHz
 Beam quality: M2 ~ 1.5
 Polarization: 99%
 Pulse width: ~ 120 s
shaping
1319nm
laser
Beam
shaping
M22
M24
Sum-freq
uency
generator
L14
LBO
 Beam parameters are optimized to achieve high
SFG efficiency
 Beam shaping optics are used to achieve beam
match between 1064&1319nm lasers
 Synchronous controller is used to achieve pulse
synchronization between the 1064nm laser
pulse and 1319nm laser pulse
laser
Synchronous
controller
TC3
M25
L15
Wavelength
controller
M25
HW3
TP5
EOM
QW3
Shutter
589output
21
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
Beam quality of M2 ~1.5 measured by
the beam quality analyzer
Linewidth of 0.6GHz measured by the
scanning interferometer
s-pulse: 500Hz, 120s
Wavelength of 589.159nm measured by
the wavelength meter
Pulse train measured by the detector
and the oscillograph
22
2. Development of TIPC sodium laser system
 50W level s-pulse solid-state sodium laser system
Wavelength calibration and control for laser system using a Na vapor
Na resonant fluorescence by CCD
1319nm seed
1319nm amplifier
1064nm seed
1064nm amplifier
Server
Controller
o-e
detector
Sum-fre
quency
Sodium
vapor
Wavelength controller
Wavelength meter
589nm output
Normal fluorescence intensity
1.00
0.95
0.90
0.85
508.844
508.846
508.848
508.850
508.852
Laser frequency (Hz)
Wavelength calibration and control
Na fluorescence intensity vs laser frequency
23
2. Development of TIPC sodium laser system
 The s-pulse sodium laser prototype 2#
Water chiller
Laser head
Power driver
Temperature controller
Master controller
Wavelength
controller
32W @500Hz
26W @600Hz
21W @700Hz
18W @800Hz
Computer
Schematic of the laser prototype
Engineering drawing
Laser prototype 2#:
150kg, 1.4m×0.72m×0.22m
24
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on UBC LZT
01-08-2013, the laser was shipped to UBC
10-08-2013, the setup of the laser with the BTO
and the LLT and the receiver telescope
12-08 to 05-09-2013, the laser on-sky tests
Launch
telescope
Laser
prototype
Beam transfer
optics
The laser with the BTO and the LLT
On-sky test team
TIPC
Prof. Bo Yong,
Dr. Zuo Junwei,
Dr. Xie Shiyong
NAOC & IOE
UBC
TMT
Prof. Hu JingYao
Dr. Feng Lu
Prof. Paul Hickson
Ronald Gagné
Dr. Angel Otá rola
Supported by
Prof. Xue Suijian
Dr. Brent
Ellerbroek
Dr. Corinne Boyer
Mr. Bill Tyler
25
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on UBC LZT
~100km
UBC
LZT
Lab
Laser
Lab
Sodium laser
system+BTO
Sodium
LGS
Rayleigh
backscatter
Launch
telescope
Receiver(0.3m) &
imaging system
Schematic of on-sky test setup
26
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on UBC LZT
The coupling efficiency with the mesospheric sodium layer was 260-300
photons-m2/s/W/ion at output power of 20W@600Hz which was more
than the TMT requirement of 130photons-m2/s/W/ion by optimizing
the wavelength, the beam spot, the polarization and so on. However, the
LGS spot was 9’’ which was bigger than the TMT requirement of 1’’
Return vs Beam spot
Return vs Wavelength
Rayleigh
backscatter
Sodium
LGS
Return vs polarization
LGS image
measured by CCD
27
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on Lijiang observatory
08-10-2013 to 22-04-2014, the on-sky tests of the laser prototype 2#
on Lijiang observatory using the 1.8m telescope by IOE & TIPC, CAS
1.8m
telescope
Of IOE
Sodium
laser of
TIPC
The Telescope with the laser prototype photo
28
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on Lijiang observatory
 Na D2b line repump
• The photon return is improved more
than 2 times if Na D2b line was
repumped (Simulation by TMT)
• The D2b repumping was achieved by
E-O modulator in the laser prototype.
Return simulation with Na D2b repumping by TMT
Na D2a and D2b pumping
The laser spectrum measured
29
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on Lijiang observatory
The launch telescope was improved from D200mm to D300mm. The
sodium LGS spot size of 3.5 arc sec was achieved and the photo return
increased by ~ 2 times when the Na D2b was repumped at 15W@500Hz
LGS spot size of 3.5 arc sec achieved
Photo return with Na D2b repumping
30
2. Development of TIPC sodium laser system
 The on-sky tests of the laser prototype 2# on Lijiang observatory
The photon return of 16.6x106 ph/m2/s was measured at output power
of 25W@600Hz, corresponding to V=6.5
Star NO. HIP43964, V=8.18, image on J band, resolution of 1.7 DL
was achieved with the sodium LGS when the AO loop is closed
Photo return of 16.6x106 ph/m2/s
measured at 25W@600Hz
The image of HIP43964 by CCD
31
2. Development of TIPC sodium laser system
 100W sodium laser system







Output power : 102 W
Wavelength : Na D2a line
Linewidth : ~ 0.3 GHz
Beam quality: M2 = 1.4
Polarization: 99%
Repetition rate: 1000Hz
Pulse width: ~ 115 s
The measured laser pulse
The measured beam quality of M2=1.40
The measured wavelength and linewidth
32
3. Summary
 Sodium laser system is one of the key device
for large ground-based telescopes to
improve high image qualities.
 Development of TIPC sodium laser system
 More than 100W output power s-pulse laser
system was developed by TIPC
 The sodium LGS of V=6.5 was generated in
on-sky tests.
 AO closed-loop images were achieved by using
the sodium LGS AO system by IOE & TIPC.
33
Thanks！
34

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