Tm- and Ho-based femtosecond lasers for 2-µm region *

University of
St Andrews
Tm- and Ho-based femtosecond lasers
for 2-µm region
A.A. Lagatsky,* and W. Sibbett
School of Physics and Astronomy, University of St Andrews, St Andrews, Fife,
Scotland KY16 9SS, UK
*[email protected]
Outline
University of
St Andrews
 2-m ultrashort-pulse laser sources and their possible applications
 Tm/Ho laser operational schemes and the prospects of ultrashort-pulse
generation
 Experimental results
- SESAMs design and characteristics
- Ultrashort pulse Tm,Ho co-doped KYW and NaYW lasers around 2 m
- In-band pumped Ho:YLF mode-locked laser
- Broadly tunable femtosecond operation in Tm:KYW
- Tm:Sc2O3: a novel medium for femtosecond pulse generation at 2.1 µm
 Conclusions
2-m femtosecond sources and their possible applications
University of
St Andrews
Molecular “fingerprint” region (2-5 µm)
© HITRAN database
Absorption line strength, 10-20 cm2/molecule·cm,
Vis.-Near-IR
Mid-IR
Wavelength
0.7-2 µm
2-5 µm
CO2
0.3
3000
CO
0.02
300
CH4
1
100
C2H2
10
200
H2O
20
200
NH3
5
10
NO
0.04
0.3
2-m femtosecond sources and their possible applications
University of
St Andrews
2-µm ultrafast
oscillator
Mid-IR
supercontinuum
Optical Fiber
2-µm ultrafast
oscillator
λi4-10 µm
 High detection sensitivity
 Broad detection range
 High-resolution
 Short acquisition time
OPO
 Mid-IR Fourier transform spectroscopy
 Real-time monitoring of atmospheric pollution;
remote chemical sensing; industrial control.
 Detection of medically important molecules, toxic
gases, drugs and explosives
 Calibration of astrophysical spectrographs
2-m femtosecond sources and their possible applications
University of
St Andrews
 3-D microstructuring of semiconductor materials
2-µm femtosecond oscillator
 Highly-localized surgery with a femtosecond 2-µm laser ?
- femtosecond pulse regime  Reduction in the shock wave
range and cavitation bubble size
Ultrafast lasers around 2m
University of
St Andrews
10000
>1nJ, >1kW
Average output power (mW)
Tm-fiber CPA
1000
Er-fiber/Raman/Tm-fiber
Tm:KLuW
Tm,Ho:YAG
(CNT)
(SESAM)
Tm-fiber
(NPE)
100
Tm:YLF (CNT)
Tm,Ho-fiber
GaSb-SDL
(SESAM)
(CNT)
Tm:GdLiF4
Tm:Lu2O3
(CNT)
(SESAM)
10
Tm,Ho-fiber
Tm-fiber
(SESAM)
(SESAM)
1
favorable
directions
Tm-fiber
(NPE)
0.1
100
1000
10000
Pulse duration (fs)
100000
Tm fiber laser with carbon nanotube absorber
University of
St Andrews
 M.A. Solodyankin, et al. Opt. Lett. 33, 1336 (2008)
92pJ, 1.32ps, 3.4mW
 Saturable absorber assisted mode-locking.
- All-fiber system
- Stable operation
- Risk of absorber damage at high energies
Tm3+-fiber laser and Tm-CPA systems
University of
St Andrews
 M. Engelbrecht, et al. Opt. Lett. 33, 690 (2008)
 F. Haxsen, et al. Opt. Express 16, 20471 (2008)
 F. Haxsen, et al. Opt. Express 18, 18981 (2010)
 F. Haxsen, et al. Opt. Lett. 35, 2991 (2010)
Chirped-pulse Tm-fiber
Amplifier
7W
25W
151 nJ, 256 fs, 5.7 W
5.4nJ, 216fs, 180mW
 NPE: nonlinear polarisation evolution mode-locking.
- Complicated design which requires a combination of fiber and
bulk optics
- Less environmentally stable
Tm3+ and Ho3+ laser operational schemes
University of
St Andrews
Tm
AlGaAs LD
 800nm
Tm,Ho
 2-2.1 m
Ho
 2-2.1 m
Tm
Ho
AlGaAs LD
 800nm
Tm-laser
 1.9-2 m
or
Tm-laser
Tm and Ho codoped laser
In-band pumped Ho laser
InGaAsSb/P
 1.9-2 µm
AlGaAs LD
 800nm
 2-2.1 m
Intra-cavity pumped Ho laser
Tm3+ and Ho3+ energy schemes
University of
St Andrews
Tm3+
25
Ho3+
ET
1
5
G4
20
4
3F
ET
4
Pump
800nm
3H
6
3
CR
Energy, 10 cm
3H
Ho3+
5I
7
Lasing
5I
8
NR
ET
-1
Tm3+
15
5
F5
3
F2,3
5
I4
3
H4
10
5
I5
UC2
CR
3
H5
5
I6
ET
3
UC1
F4
5
5
I7
Pump
Laser
3
5
H6
0
I8
Intensity, a.u.
14
 Up-conversion losses in the Tm or
Tm-Ho systems could prevent highpower operation
3
F2, K8
F3
5
5
S2, F4
5
5
5
S2- I8 (Ho)
Ppump=1.2W
12
1% OC
2% OC
4% OC
no lasing
10
8
6
1
3
G4- H6 (Tm)
4
5
5
F3- I8 (Ho)
5
5
F5- I8 (Ho)
3
3
F2,3- H6 (Tm)
2
0
400
450
500
550
600
Wavelength, nm
650
700
Tm3+ vs Ho3+ for ultrafast lasers
University of
St Andrews
 Ho3+ (4f10 electronic configuration) features optical absorption and emission bands with
the usual sharpness of most trivalent lanthanides (i.e., those with 4fN N<11 electronic
configurations)
 Tm3+ : 4f12 electronic configuration - inhomogeneous broadening of electronic transitions
Ho3+:KYW
Tm3+:KYW
3.0
5
2
cm
3
2
1
0.5
0.0
1600
4
-20
1.0
EllNm
E ll Nm
em, x10
2
-20
1.5
cm
2.0
em, x10
2.5
1700
1800
1900
2000
Wavelength, nm
FWHM 170nm
2100
2200
0
1900
1950
2000
Wavelength, nm
FWHM  15 nm
2050
Water vapor transmission around 2m
University of
St Andrews
1.0
Transmission
0.8
0.6
0.4
1mm H2O
0.2
0.0
1.8
1.9
2.0
2.1
2.2
Wavelength, m
 Water vapor absorption could prevent continuous tunability and broadband
modelocking in a Tm/Tm,Ho laser system
 OH- containing liquids are prone to bleaching effects on nanosecond time scale initiating
Q-switching instabilities in a solid-state laser system
Tm-Ho codoped KYW laser
University of
St Andrews
Tm(5at%), Ho(0.5at%):KYW, EllNm, L=1.5mm
2
1
0
-1
-2
-3
-4
1880
1920
1960
2000
2040
Wavelength, nm
2080
450
400
350
300
250
200
150
100
50
0
1850
Ppump=1.2 W
1% OC
140
120
100
80
60
40
20
1900
1950
2000
2050
-1
 = Ne/Nt
Water absorption, cm
3
 = 0.1
 = 0.2
 = 0.3
 = 0.4
 = 0.5
 = 0.6
 = 0.7
Tm,Ho:KYW tunability
Output power, mW
Gain cross-section, x10
-20
cm
2
Gain spectra
0
2100
Wavelength, nm
A.A. Lagatsky et al, “Spectroscopy and efficient continuous wave
operation of Tm,Ho:KYW near 2 m”, Appl. Phys. B 97, 321 (2009).
SESAM structures design
University of
St Andrews
Low-finesse A-FPSA (SBR structure)
0.4
102
0.3
4.4
0.2
4.0
0.1
3.6
0.0
3.2
20xGaSb/AlAsSb BDR
2.8
-0.1
0
500 1000 1500 2000 2500 3000
Thickness (nm)
Reflectivity (%)
+
2xInGaAsSb QWs
Refractive index
E-field (a.u.)
4.8
N ion implantation
100
98
96
12
94
92
90
1900
-2
5x10 cm
12
-2
2.1x10 cm
12
-2
1x10 cm
as grown
1950
2000
2050
2100
Wavelength (nm)
Absorber structure
10nm
GaSb protective cap
41nm
Al0.24Ga0.76As0.021Sb0.979
5.5nm In0.4Ga0.6As0.14Sb0.86
20nm
QW
Al0.24Ga0.76As0.021Sb0.979
5.5nm In0.4Ga0.6As0.14Sb0.86
QW
50.85nm Al0.24Ga0.76As0.021Sb0.979
0.61nm GaSb protective layer
A0=0.5-2% @ 2000-2100 nm
QW PL peak = 2100 nm
2150
Experimental set-ups:
(Tm,Ho:KYW, NaYW and Tm:KYW)
La ser ca vity
Pump configura tions
Ti:S Pump
1.2 W @ 800 nm
University of
St Andrews
OC 1%
Tm,Ho:NaYW, KYW
63mm
M1
FS
TLD Pump
1.2 W @ 802 nm
75mm
M2
AL
SESAM
CL
wpumpwcavity = 28 m; wSESAM=80-140 m
M1 and M2: HT@800nm & HR@1800-2100nm, r=-100mm
FS: IR-grade fused silica prisms
Single prism insertion: GVD  -114 fs2
Tip-to-tip prisms separation:  8 cm (double pass GVD -1200 fs2)
Femtosecond Tm,Ho:KYW laser
University of
St Andrews
120
ML,thr
FSESAM =42.7 J/cm
sech
2
100
80
Intensity, a.u.
ML Output power, mW
140
ML threshold
60
Q-ML
40
0.8
=7.9 nm
2
0.8
p=570 fs
=0.32
0.4
0.4
CW
20
0.0
0.0
0
0
200
400
600
800
1000
Absorbed pump power, mW
1200
-2
0
Delay, ps
2
2040
2060
2080
Wavelength, nm
Stable ultrashort-pulse operation was observed when the fluence on the SESAM exceeded 42.7 J/cm2.
Pulses as short as 570 fs were generated at average output power of 130 mW and pulse repetition
frequency of 118 MHz, this corresponded to 1.1 nJ of the pulse energy and 1.9 kW of the peak power.
A.A. Lagatsky et al, “Femtosecond pulse operation of a Tm,Ho cocodoped crystalline laser near 2 m”, Opt. Lett. 35, 172-174 (2010).
Tetragonal double tungstates
University of
St Andrews
Ho3+ drawback
Ho3+ (4f10 electronic configuration) features optical absorption and emission
bands with the usual sharpness of most trivalent lanthanides (i.e., those with 4fN
N<11 electronic configurations)
~ 10-15 nm for KYW
Partial solution: locally disordered crystals
MT(XO4)2 : (M= Li+, Na+); (T= La3+, Gd3+, Lu3+ or Y3+); (X=Mo6+ or W6+)
NaY(WO4)2: Czochralski growth method
Yb3+ - ~ 50 fs pulses [A. García-Cortés, et al. IEEE J. Quant. Electron. 34, 758 (2007)]
Tm3+ - 1850-2070 nm tunability [M. Rico, et al. in Advanced Solid-State Photonics,
2009, WB27]
CW Tm,Ho codoped NaYW lasers
University of
St Andrews
Tm(5at%),Ho(0.25at%):NaYW
300
 - polarisation
Pabs=1 W
200
100
FWHM 142 nm
0
1850 1900 1950 2000 2050 2100
Wavelength, nm
L=3.8 mm,
Output power (mW)
Output power, mW
L=3.8 mm,
Tm(5at%),Ho(0.25at%):NaYW
350
300
250
200
150
100
50
0
 - polarisation
Pabs=0.95 W
FWHM=130 nm
1850 1900 1950 2000 2050 2100
Wavelength (nm)
Modelocked Tm,Ho:NaYW (-pol.)
24.8nm
=0.33
17.6nm
=0.32
160
Q-switching
Modelocking
140
258 fs
120
100
588 fs
80
Intensity (a.u.)
1.0
Tm,Ho:NaYW
luminescence
0.5
191 fs
60
0.0
2000
40
20
500 fs
2040
2080
2120
Wavelength (nm)
0
0
200
400
600
800
1000
p=191 fs
1.0
p=258 fs
Absorbed pump power (mW)
PRF=144 MHz
Ep=1.08 nJ, P=4.2 kW
FSESAM=80-190 J/cm2
Intensity (a.u.)
Average output power (mW)
University of
St Andrews
2
sech fit
0.5
0.0
-1.0
-0.5
0.0
0.5
1.0
Delay (ps)
A.A. Lagatsky et al, “Femtosecond (191-fs) NaY(WO4)2 Tm,Hocodoped laser at 2060 nm”, Opt. Lett. 35, 3027-3029 (2010).
Modelocked Tm,Ho:NaYW (-pol.)
University of
St Andrews
600
D=-2100 fs
500
-7
=2.95x10 W
400
-7
=7.8x10 W
300
dp/dlDl=0.111 fs
2
Pulse duration, fs
Pulse duration (fs)
440
-1
-1
400
-1
Ep=107.5 nJ
360
320
280
200
240
20
30
40
50
60
70
80
90
100
-3500
Intracavity pulse energy (nJ)
 p  1.7627

2

n2
Lg
Aeff
D, fs
d p
2D
  Ep
-3000
dD
-2500
-2000
2
 1.7627
2
  Ep
n2=16.4x10-16 cm2/W @ 2060 nm
n2=30x10-16 cm2/W @ 820 nm [A. García-Cortés, et al. Appl. Phys. B 91, 507 (2008)]
TLD pumping of Tm,Ho codoped KYW and NaYW
University of
St Andrews
farfield position
beamwaist position
Eagleyard Photonics GmbH
Pout=2 W @ 802 nm
M2 ~ 5, PCL=80%
Tm,Ho:KYW, Pout=200mW
1.0
=675 fs
sech
0.5
=0.32
=0.32
1.0 =355 fs
=6.7 nm
2
0.5
0.0
-2
0
Delay, ps
2
0.0
2020 2040 2060 2080
Wavelength, nm
Intensity, a.u.
Intensity, a.u.
1.0
Tm,Ho:NaYW, Pout=120mW
1.0
sech
0.5
2
=12.6 nm
0.5
0.0
0.0
-1
0
Delay, ps
1
2000
2050
2100
Wavelength, nm
In-band pumped Ho:YLF ultrafast laser
University of
St Andrews
N. Coluccelli, A.A. Lagatsky et al, “Passive mode locking of in-bandpumped Ho:YLiF4 laser at 2.06m”, Opt. Lett. 36, 3209 (2011).
In-band pumped Ho:YLF ultrafast laser
University of
St Andrews
1%OC
4%OC
Pout=1.7W (4% OC), PRF=122 MHz, Ep=13.9 nJ
Efficient and broadly tunable Tm:KYW laser
University of
St Andrews
700
Output power, mW
600
Tm(5at%):KYW, L=2mm
Epump ll Nm, kpump ll Ng
Free lasing
1% and 2% OCs
500
400
Lyot filter
FWHM=172 nm
300
200
FS prism
T=1%
Pin=1.2 W
100
277 nm
0
1850
1900
1950
2000
2050
Wavelength, nm
2100
2150
=73% (82% theoretical
limit) @ 1940 nm
=48% @ 2060 nm
Tunable Mode-locking of Tm:KYW
University of
St Andrews
FS
63 mm M1
Knife
edge
Tm:KYW
OC
Ti:sapphire
P = 1.2 W
M2
SESAM
wpumpwcavity = 28 m; wSESAM=142 m
M1 and M2: HT@800nm & HR@1800-2100nm, r=-100mm; OC – 1% output coupler
FS: IR-grade fused silica prisms (GVD=-114fs2/mm)
Single prism insertion  6 mm (double pass GVD  -1370 fs2)
Tip-to-tip prisms separation: 9 cm (double pass GVD -1800 fs2)
Broadly tunable ML with a single prism
1200
Intensity, a.u.
1350
SESAM#2
1050
900
750
1.0
sech
2
0.5
-2
400
360
320
280
240
200
1980
p=549 fs
0.0
600
Intensity, a.u.
Average power, mW
Pulse duration, fs
University of
St Andrews
2000
2020
2040
Wavelength, nm
2060
2080
0
Delay, ps
2
1.0 FWHM=8 nm
0.5
0.0
1960 1970 1980 1990 2000 2010
Wavelength, nm
Tunability: 1985nm (549fs, 410 mW) – 2074nm (1.32ps, 210mW)
Pulse energy: 3.9 nJ
Peak power: 7.1 kW
A.A. Lagatsky et al, “Broadly tunable femtosecond mode-locking in a
Tm:KYW laser near 2µm”, Opt. Express 19, 9995 (2011).
Optimised pulse duration
900
1.0
800
SESAM#2
700
SESAM#1
Intensity, a.u.
1.0
600
500
p=386 fs
11.14 nm
0.5
0.5
0.0
0.0
400
-2
240
210
180
150
120
90
1980
2000
2020
2040
Wavelength, nm
2060
RF power density, dBm
Average power, mW
Pulse duration, fs
University of
St Andrews
0
Delay, fs
2
2000 2040 2080
Wavelength, nm
-40
-60
-80
69 dBc
Span 50 kHz
RBW 300 Hz
-100
-120
97.36 97.37 97.38 97.39 97.40
Frequency, MHz
 p=386 fs, Average power: 235 mW; Pulse energy: 2.4 nJ (peak power 6.2 kW)
 Modelocking thresholds: 252 J/cm2 and 227 J/cm2 on the SESAMs #1 and #2
Mode-locking stability in Tm:KYW
University of
St Andrews
Pulse duration, fs
1350
Q-switching instabilities
1200
1050
Q-switching
or CW
900
750
600
400
0.8
360
320
0.6
280
0.4
240
200
1900
0.2
1920
1940
1960
1980
2000
Wavelength, nm
2020
2040
2060
2080
Transmission
Average power, mW
1.0
Tm-doped sesquioxides (Sc2O3, Lu2O3, Y2O3)
University of
St Andrews
 P. Koopmann, et al, “Long wavelength laser operation of Tm:Sc2O3 at 2116 nm
and beyond”, ASSP 2011, paper ATuA5.
Gain spectra of Tm:Sc2O3
k=16.5 W/m·K (11 W/m·K for YAG)
 Tm:Sc2O3 cw laser
Pout=26W (70W pump @ 796nm)
Tm:Sc2O3 femtosecond laser
University of
St Andrews
Experimental set-up
OC
SWPF
-100mm
2.6W @ 796nm
FS
Dual wavelength operation
Tm:Sc2O3
SWPF
12
600
2115.5 nm
-100mm
10
1998 nm
8
400
6
300
200
4
100
2
0
1950
0
2000
2050
Wavelength, nm
2100
2150
Transmission, %
SESAM
Intensity, a.u.
500
Tm:Sc2O3 femtosecond laser
University of
St Andrews
250
600
200
500
ML
150
QS-ML
400
100
CW
50
300
0
200
0
200
400
600
800
1000
1200
Absorbed pump power, mW
1400
1600
Pulse duration, fs
700
Intensity, a.u.
T=2.3%
300
Output power, mW
1.0
800
p=218 fs
PRF=118.8 MHz
TBP=0.32
2
0.5
sech
0.0
-0.8
-0.4
0.0
0.4
0.8
Delay, ps
1.0
Intensity, a.u.
350
P=210 mW
=2107nm
=21.7 nm
0.5
0.0
2040
2080
2120
Wavelength, nm
 p=218 fs, Average power: 325 mW; Pulse energy: 2.6 nJ (PRF=123 MHz)
 Modelocking threshold: 32.4 J/cm2 of intracavity fluence on the SESAM
2160
2200
Ho and Tm crystalline femtosecond lasers
University of
St Andrews
𝑷𝒎𝒂𝒙
𝒂𝒗 , mW
𝝉𝒎𝒊𝒏
𝒑𝒖𝒍𝒔𝒆 , fs
Tm,Ho:KYW
130
570
1.1
2055
-
Tm,Ho:NaYW
155
191
1.08
2058
2016-2066
Ho:YLF
1700
1100
13.9
2064
-
Tm:KYW
410
386
3.9
2029
1985-2074
Tm:Sc2O3
325
218
2.6
2107
-
Laser
Epulse , nJ λc, nm
Tunability, nm
Ho and Tm crystalline femtosecond lasers
University of
St Andrews
10000
Tm-fiber CPA
Tm-fiber CPA
Output power, mW
Ho:YLF
1000
Tm:Sc2O3
Tm:KYW
Tm-fiber
100
Tm,Ho:KYW
Tm,Ho:NaYW
10
100
1000
Pulse duration, fs
Acknowledgements
University of
St Andrews
 James Gupta
Institute for Microstructural Sciences, National Research Council of Canada, Ottawa,
Canada
 Stephane Calvez
Institute of Photonics, University of Strathclyde, Glasgow, UK
 Viktor Kisel and Nikolai Kuleshov
Institute for Optical Materials and Technologies, Belarus National Technical
University, Minsk, Belarus
 Carlos Zaldo
Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones
Científicas, Madrid, Spain
 Nicola Coluccelli and Paolo Laporta
Dipartimento di Fisica - Politecnico di Milano and Istituto di Fotonica e
Nanotecnologie - CNR, Milano, Italy,
 Philipp Koopmann and Günter Huber
Institute of Laser Physics, University of Hamburg, Hamburg, Germany