High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with...
Transcript of High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with...
![Page 1: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/1.jpg)
High Power Operation of Cryogenic Yb:YAG
K. F. Wall, B. Pati, and P. F. MoultonPhotonics West 2007
San Jose, CAJanuary 23, 2007
![Page 2: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/2.jpg)
Outline
• Early work on cryogenic lasers• MPS laser technology• Recent program on high-power cryogenic Yb:YAG
![Page 3: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/3.jpg)
Early Cryogenic Laser Technology
![Page 4: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/4.jpg)
Reasons for Cryogenic Cooling
of Solid State Lasers
• Thermal– Increased thermal conductivity of host crystal at low
temperatures• Reduced heat rise inside crystal, reduced thermal gradient• Reduced stress, allowing higher power output/unit volume
– Reduced thermo-optic distortion in crystal
• Spectroscopic– Reduced population in lower level for 3½-level lasers– Increased upper-laser-level lifetime for laser transitions that
are thermally quenched– Stability of laser-active ion (for color-center lasers)
![Page 5: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/5.jpg)
Bowness Patent: Liquid Nitrogen Cooled Ruby Laser (1963)
![Page 6: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/6.jpg)
McMahon Patent on Cryo-Cooled Ruby (1969)
![Page 7: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/7.jpg)
McMahon apparatus
![Page 8: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/8.jpg)
First Broadly Tunable Lasers were Cryo-Cooled (1963)
![Page 9: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/9.jpg)
Doehler and Solin system (1972)
![Page 10: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/10.jpg)
Back and Gurs Cryo-Cooled cw Ho:YAG Laser (1975)
![Page 11: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/11.jpg)
Work on Cryogenic Lasers Extends Back to 1978
Publications (at MIT/LL)
P.F. Moulton, A. Mooradian and T.B. Reed, "Efficient cw Optically Pumped Ni:MgF2
Laser," Opt. Lett. 3, 164 (1978).
P.F. Moulton and A. Mooradian, "Broadly Tunable CW Operation of Ni:MgF2
and Co:MgF2
Lasers," Appl. Phys. Lett. 35, 838 (1979).
P.F. Moulton, "Pulse-Pumped Operation of Divalent Transition-Metal Lasers," IEEE J. Quantum Electron. QE-18, 1185 (1982).
P.F. Moulton, "An Investigation of the Co:MgF2
Laser System," IEEE J. Quantum Electron. QE-21, 1582 (1985).
Products (at Schwartz Electro-Optics, now Q-Peak)
CW Co:MgF2
lasers (5 W power) built and shipped to Northwestern University and White Sands Missile Range, NM (circa 1990)
![Page 12: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/12.jpg)
Cryogenic Laser Designs at MIT/LL
![Page 13: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/13.jpg)
Average Power Levels in the 7-10 W range were Obtained, Limited by the Pump Source
Pulsed Ni:MgF2
laser pumped by Nd:YAP laser at 1.34 um (MIT LL Solid State Research 1982:1)
CW Ni:MgO laser pumped by Nd:YAG laser at 1.065 um (MIT LL Solid State Research 1981:1)
Both lasers operated in the TEM00 mode, because of the high thermal conductivity of the laser crystals at liquid nitrogen temperature
![Page 14: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/14.jpg)
Photos of Cryogenic Lasers at MIT/LL (1978-1985)
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Yb:YAG Cryogenic Laser Technology
![Page 16: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/16.jpg)
Diode Pumps have Enabled Yb:YAG lasers
Energy levels in Yb:YAG
968 nm
10679 cm-1
1062410327
785612565
0
1030 nm941 nm
2F7/2
2F5/2
Ener
gy
Yb:YAG absorption spectrum, 77 and 300 K
900Abs
orpt
ion
Coe
ffici
ent (
cm-1
)
Wavelength (nm)
0
2
4
6
8
10
920 940 960 980 1000 1020 1040
Laser
Wavelength
77 K
300 K
![Page 17: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/17.jpg)
General Issues for High-Power Solid State Lasers
Distortion (OPD) Depolarization
h
fractional thermal load thermal conductivity
thermal expansiondn/dT
change in refractive index with temperature
FOMd
=
/ [h
dn/dT] FOMb
=
/ h
• Larger material FOM’s give less distortion, stress-induced birefringence• Key material properties (, , dn/dT) expected to scale favorably at lower
temperature in bulk single crystals• FOMb
is irrelevant in birefringent media since there will be no depolarization (unless propagating down optical axis)
• Assumes equal laser efficiency
Courtesy: T.Y. Fan, MIT/LL
![Page 18: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/18.jpg)
Cryo-cooled Yb:YAG has Greatly Enhanced Potential High-Power Performance
• FOMb
and FOMd
>30X larger in 100 K Yb:YAG compared with 300 K Nd:YAG– ~ >12X larger than 300 K Yb:YAG (assuming equal optical efficiencies)
• Broad absorption band maintained at low temperature– Sharpening of absorption features at low temperature does not drive pump
wavelength control requirements
Courtesy: T.Y. Fan, MIT/LL
![Page 19: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/19.jpg)
MIT/LL Cryo
Yb:YAG Laser Technology
Pump Diodes
Polarizers
• Breadboard features– Yb:YAG cryogenically cooled in LN2
cryostat– Efficient end-pumping with high-brightness diode pump lasers – Yb:YAG crystal indium soldered to copper mount for heat-sinking– Large beam radius (~ 1 mm) resonator to avoid optical damage
Laser Output
AOM Q-Switch
Beam Profile
Output
Coupler
LN2
Dewar
Yb:YAG Crystal
![Page 20: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/20.jpg)
MIT/LL has Shown Steady Progression of Power
Proof-of-principle demonstration at MIT LL in 1997 40 W: Fan et al, Proc SPIE, v 3381, 200 (1998)165 W: Ripin et al, Opt. Lett, v 29, 2154 (2004)300 W: Ripin et al., IEEE JQE, v 41, 2174 (2005)
MIT now planning to build cryo Yb:YAG modules for possible insertion into ABL
![Page 21: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/21.jpg)
David Brown’s paper, 2005
![Page 22: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/22.jpg)
Q-Peak’s Approach to Cryogenically Cooled Yb:YAG Lasers
![Page 23: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/23.jpg)
Q-Peak’s MPS DPSSL Design Obtains High Efficiency, High Beam Quality with Side-Pumping
Multi-Pass Slab (MPS)Materials: Nd:YLF, Nd:YVO4
Yb:S-FAP, Yb:YAG, Tm:YLF, Er:YLF“Gain Module”
![Page 24: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/24.jpg)
MPS Nd:YLF CW oscillator performance
scales with pump lasers
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70 80
Pump Power (W)
Out
put P
ower
(W)
40 W, MM30 W, MM30 W, TEMoo20 W, TEMoo
M2
= 1.05
![Page 25: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/25.jpg)
Goals of Newest Cryo
Laser Program at Q-Peak
• Design a side-pumped breadboard 250-W Q-switched Yb:YAG laser, with the capability of cooling to cryogenic temperatures.
• Construct the 250-W Yb:YAG laser and measure the multimode, multi-
passing, and repetitively Q-switched performance, at cryogenic temperatures.
• Achieve a goal for the laser beam quality of M2
≤
2 and a goal for the Q-switch repetition rate of 5 kHz without optical damage.
Program funded by AFRL Phase II Contract # FA9451-04-C-0151
![Page 26: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/26.jpg)
Cryo Yb:YAG crystal is a 4-mm-thick slab
• Crystal is 2% doped and 28 x 10 x 4 mm in size.
• Two pump diode laser arrays are offset on the opposite sides of the slab.
• Heat is removed from the two large faces of the crystal.
![Page 27: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/27.jpg)
Model thermal distribution in Yb:YAG crystal
The maximum temperature occurs at the pump faces and is 25º higher than the faces in contact with the heat sinks.
![Page 28: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/28.jpg)
Crystal Mount Achieves Effective Cooling
![Page 29: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/29.jpg)
Sectional View of Model Temperature Distribution
• Temperature of the center of the crystal is ~ 129 °K .
• Crystal surface-temperatures at the interfaces of the base and clamp plates are 90 °K and 101 °K respectively.
• Heat removal from the crystal mount is only from the base plate.
• Bottom surface at 100 K• Uniform heat deposition of 360 W in the crystal.• Perfect contact between the crystal and heat sinks. Also,
perfect contact between the base and clamp plates.
Assumptions:
![Page 30: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/30.jpg)
Schematic of TEM00
Resonator Design (Under Construction)
![Page 31: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/31.jpg)
Calculated Beam Sizes of Cavity
•Assumes weak thermal lensing
•Stable, but very sensitive to mirror misalignment
![Page 32: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/32.jpg)
Nuvonyx Diode Arrays are High-Power Side Pumps
![Page 33: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/33.jpg)
Pump Focusing Design Uses Simple Optics
Top view
Sideview
![Page 34: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/34.jpg)
Pump Beam at Crystal Face
•Imaged at the plane of crystal surface
•Intensity of the beam was reduced by operating the laser in pulse mode
•Beam size 10 X 2 mm
•CCD camera and Spiricon beam analyzer.
![Page 35: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/35.jpg)
Experimental Setup of Cryo
System uses Large Dewar for long run times
![Page 36: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/36.jpg)
Multi-Mode Resonator Design used for Initial Demo
• The laser was multi-mode in the horizontal plane and nearly diffraction limited in the vertical plane.
• 98% of pump power was incident on the crystal and 98% was absorbed.
50-cm cc HR
Yb:YAG
Flat OC
18 cm
12 cm
![Page 37: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/37.jpg)
High-efficiency Multimode Lasing is Obtained
• Maximum output power was 400 W with a total pump power of 720 W.
• With 80%-reflective output coupler, the slope efficiency was 62% and optical-to-optical efficiency was 56%.
0
100
200
300
400
500
0 200 400 600 800
Pump power (W)
Out
put p
ower
(W)
![Page 38: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/38.jpg)
Measured Temperatures at Crystal Base and Clamp Plates Show Heat Load Lasing, Non-Lasing
• Compared with the lasing condition, in the non-lasing condition, the temperatures of the clamp and base plates were 26 °K and 11 °K higher respectively.
Non-lasing condition Lasing condition
70
80
90
100
110
120
130
0 200 400 600 800
Pump power (W)
Tem
pera
ture
(K) Base plate
Clamp plate
70
80
90
100
110
0 200 400 600 800
Pump power (W)Te
mpe
ratu
re (K
) Base plate
Clamp plate
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Measured Probe-Beam Deflection in the Crystal
• Thermal wedging due to the temperature difference between the top and bottom of the crystal.
• Camera was 1 m away from the crystal.
• Beam deflection is prominent in the vertical plane
• Calculated thermal wedging in the vertical plane is ~ 0.7 mrad
-0.5
0
0.5
1
1.5
0 200 400 600 800
Pump power (W)
Bea
m d
efle
ctio
n (m
m)
Horizontal
Vertical
![Page 40: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/40.jpg)
Preliminary 5-Pass Measurements
0
100
200
300
400
0 200 400 600 800
Pump power (W)
Out
put p
ower
(W)
• We are still working on optimizing the cavity design
![Page 41: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/41.jpg)
Measured Energy per Pulse and Pulse Width as a Function of Repetition Rate
0
10
20
30
40
50
60
70
0 5 10 15 20
Repetition rate (kHz)P
ulse
wid
th (n
s)
The laser was QCW pumped at 25% duty cycle.
0
5
10
15
20
25
0 5 10 15 20
Repetition rate (kHz)
Ener
gy (m
J)
![Page 42: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/42.jpg)
Laser Pulse and Beam Profile at 18-kHz Repetition Rate.
The laser was QCW pumped at 50% duty cycle.
![Page 43: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/43.jpg)
Future (?) Improved Cryo
Cooling System
• Continuous LN2
pumping through the base and clamp plate of the crystal.
![Page 44: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/44.jpg)
Pump Lasers
• Fiber coupled sources are available in a variety of configurations
• Up to 750 W in a 400 um core fiber (NA = 0.22), with further improvements in power expected in the future
![Page 45: High Power Operation of Cryogenic Yb:YAG 2007 Cryo Yb_YAG.pdfJan 23, 2007 · Laboratory with Yb:YAG systems • We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.](https://reader034.fdocuments.in/reader034/viewer/2022051606/601679a79daff2191d088c5e/html5/thumbnails/45.jpg)
End-pumped Cryo
Yb:YAG could be Seed Oscillator for High-Power System
Mirrors
HR at 1.03 µm
HT at 0.94 µm
Yb:YAG
in Dewar
940-nm
Pump
Radiation
Optical
Fiber
= 2.2 mm
NA = 0.12
1.03 µm
Output
R = 75%
Drawing courtesy: T.Y. Fan, MIT/LL
Fan et al, Proc. SPIE
v 3381, 200 (1998)
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Q-switched Cryo
Yb:YAG
Estimates
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35 40
Cavity length (cm)
Puls
ewid
th (n
s)
10X
20X
Ratio over threshold
0
10
20
30
40
50
60
70
80
90
100
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11
Cavity mode radius (cm)Po
wer
out
put (
W)
Pulsewidths from 5-60 ns are Possible at 5-kHz Pulse Rates
Average Powers from Cryo Yb:YAGDepend on Achievable Mode Size
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Conclusions
• Q-Peak has returned to the development of cryogenic laser technology, following on the recent efforts at MIT Lincoln Laboratory with Yb:YAG systems
• We have demonstrated a 400 W, cw, cryogenically cooled Yb:YAG laser.
• We obtained a slope efficiency of 62% and optical-to-optical efficiency of 56% in a side-pumped slab geometry, in good agreement with our estimates.
• The laser is multi mode in the horizontal plane and nearly diffraction limited in the vertical plane.
• Beam quality will be improved by multi passing the laser in the crystal –
experiments underway, along with Q-switching.