Nd:YAG laser terminal level relaxation time direct evaluation and its considering at picosecond pulse amplification

1.

Nd:YAG laser terminal level relaxation time
direct evaluation and its considering
at picosecond pulse amplification
V.B. Morozov
A.N. Olenin
D.V. Yakovlev
Physics Faculty
of M.V.Lomonosov Moscow State University
Moscow, Russia
LHPHYS’
ICLO 2024
2017
July
July1–5
17-21
StPetersburg
Kazan

2.

Nd:YAG : 1064 nm laser transition
I.E.Geusic, H.M.Marcos, L.G.Van Uitert.
Appl.Phys.Lett.,4(10) 182-184 (1964)
Classical 4-level scheme
Simplified level structure
Fluorescence lifetime:
tFL= 230ms
Stimulated emission cross
section:
s = 2,8×10-19 cm2

3.

Nd:YAG: 1064 nm and other laser transitions
Simplified level structure
4F
4F
4
3/2- I11/2
1064 nm
4-level
4
3/2- I13/2
1320 nm
4-level
946 nm
3-level
4F
4
3/2- I9/2

4.

Nd:YAG: picosecond pulse generation
Fluorescence lifetime:
tFL= 230ms
Stimulated emission cross section:
sF = 2,8×10-19 cm2
Transition bandwidth (FWHM):
Passive mode-locking
Dn0 /c = 4,3 cm-1 или Dn0 =130∙109 c-1
4,95
Г
For a Lorentzian line:
t
PML
p ,min
6 ps
For pulsed Nd:YAG
lasers typically:
t
PML
p
25...30 ps
Active mode-locking
14
t
AML
p
gl 0
3,3
M
1
F Г
70...150 ps
Herman A.Haus, Mode-Locking of Lasers.
IEEE J.Sel.Top.QE, 6(10) 1173-1185, 2000
g L
g L0
2 0
1
Г
2
Г 2 Dn 0
F 2 n F 2 Trt c L

5.

Applications of high-peak and average power
picosecond lasers
А
Time-resolved and time-domain
spectroscopy
1
2
Cold laser ablation
А
Machining of thermally sensitive materials
Satellite laser ranging
Lunar laser ranging
0
density , Amagat
-2
-4
6.6x10
-4
Photocathode laser drivers
-6
lg(Wa(t)/Wa
norm
)
2.6x10
-3
-8
OPO pumping
-3
8x10
-10
0.025
-12
0.05
-14
0.1
0.2
-16
0.4
3
-18
8
-20
20
0
1
2
4
6
8
time delay, ns
10
12
14
etc.

6.

Applications of high-peak and average power
picosecond lasers
Time-resolved and time-domain
spectroscopy
Cold laser ablation
Machining of thermally sensitive materials
Satellite laser ranging
Lunar laser ranging
Photocathode laser drivers
OPO pumping
etc.

7.

Applications of high-peak and average power
picosecond lasers
Time-resolved and time-domain
spectroscopy
Cold laser ablation
Machining of thermally sensitive materials
Satellite laser ranging
Lunar laser ranging
Photocathode laser drivers
OPO pumping
etc.

8.

Applications of high-peak and average power
picosecond lasers
Time-resolved and time-domain
spectroscopy
Cold laser ablation
Machining of thermally sensitive materials
Satellite laser ranging
Lunar laser ranging
Photocathode laser drivers
OPO pumping
etc.

9.

Conception for energy effective pulsed
picosecond laser of high peak and average power
Simple and energy effective approach for practical high peak-power systems
based on Nd-doped laser crystal design
• Master oscillator with necessary characteristics (active/passive mode-locked laser, or
passively Q-swiched microchip laser, or gain-swiched laser diode etc.);
• Regenerative amplifier from pico/nano/microJoule to milli-Jole level;
• End-amplifying up to multi-milli-Joule level using linear amplifier stages;
• Near saturation regime at output amplifier stages;
• Double-pass amplifying schemes;
• Effective diode-pumping schemes;
• End-pumping geometry etc.
Saturation fluence
FS
h n L
sE
Nd:YAG:
FS ≈ 0.67 J/cm2
1 … >10 mJ
1…5 mJ
pJ/nJ/μJ
ps Master
Oscillator
Achievable output pulse energy:
Saturation fluence × Mode cross section
~ 0.5 J/cm2 × 0.2 mm2 ~ 1 mJ
Regen
Amp
Linear
Amps

10.

Picosecond laser with active-passive mode-locking,
regenerative amplifier and two linear amplifiers
Picosecond Nd:YAG laser PL-PDP-3114SH
Wavelength:
1064 / 532 nm
Pulse length:
25 ps
Single pulse energy:
PUMPING
to Master
oscillator
to Reg
amplifier
to Amp 1
to Amp 2
5.0 mJ / 2.5 mJ
Repetition rate:
1 kHz
Beam quality M2
within 1.2

11.

Picosecond laser with active-passive mode-locking,
regenerative amplifier and two linear amplifiers
Picosecond Nd:YAG laser PL-PDP-3114SH
Wavelength:
1064 / 532 nm
Pulse length:
25 ps
Single pulse energy:
5.0 mJ / 2.5 mJ
Repetition rate:
1 kHz
Beam quality M2
within 1.2
Principal optical scheme of end-pumped amplifier
Pump beam
condenser
From regenerative amplifier
Laser crystal
l/4
Pump
Convex
mirror
Telescope
to output
Calcite
polarizing prism

12.

Simplified diagram of two-pass amplifier operation
at picosecond pulse amplification
t : upper level lifetime
t : laser pulse duration
t : terminal level relaxation time
FL
P
P

13.

Energy levels of Nd3+ ions in YAG matrix at 300K
etc.
G.M.Zverev, Yu.D.Golyaev, E.A.Shalaev, A.A.Shokin.
Neodymium dopped yttrium aluminum garnet lasers, 1985

14.

Characeristic radiative and nonradiative times of
Nd3+ ions in YAG matrix at 300K
b3j is luminescence
branching factor
G.M.Zverev, Yu.D.Golyaev, E.A.Shalaev, A.A.Shokin.
Neodymium dopped yttrium aluminum garnet lasers, 1985

15.

Results on low laser level evaluation in Nd:YAG
G.M.Zverev et
al.
A.A.Zlenko et
al.
A.A.Zlenko et
al.
V.P.Gapontse
v et al.
T.Kushida et
al.
V.V.Grigor’ya
nts et al.
J.Cruz et al.
Lifetime
(ns)
~500
<300
<30
Reference
Sov.Phys.JETP
33(497)1971
Sov.J.Quant.El.
2(474)1973
ibid
Experimental
methods
Gap Law (4G7/2
lifetime)
Gain recovery
Other
~10
In Proc. Las. (STS,
McLean, Va.) p.63,
1981
Other
<10
Sol.St.Com.
44(1363)1982
Sov.J.Quant.El.
12(1010)1983
Opt.Lett.
15(282)1990
In Adv. Solid-state
Lasers, OSA
Proc.Ser.
10(358)1991
In Adv. Solid-state
Lasers, OSA
Proc.Ser. 15(78)1991
Gap Law (4G7/2
lifetime)
Other
IEEE J.QE
28(39)1992
JOSA B
12(1981)1995
2007
2011
Gain recovery
<10
0.47
T.T.Basiev et
al.
0.37
K.Palombo et
al.
<5
F.E.Hovis et
al.
C.Bibeau et
al.
<11
0,1750,225
Gap Law (4G7/2
lifetime)
Gap Law (4G7/2
lifetime)
Gain recovery
Pump-probe
The issue of the terminal level relaxation time
periodically has attracted attention from many groups.
The results are distributed quite widely
Generally, it should be noted that all measurements are
based anyway on the results of indirect rather than
direct measurements.
It should also be noted that the values ​were gradually
refined towards their decrease.

16.

Results of C.Bibeau et al. (1995)
on low laser level evaluation in Nd:YAG
Nd:YAG 1064 nm line terminal level relaxation time
tTL= 170 ± 55 ps
C.Bibeau, S.A.Payne, and H.T.Powell. JOSA B 12(10) 1981-1992 (1995)

17.

Double-pass amplifier modelling
E
hn12
nonradiative
N2
N1, t10
N0
LA LR
LA
LR
12
11
6,5
10
6,0
5,5
9
5,0
8
0
100
200
300
0
20
40
60
80
100
delay length 2LR, mm / time delay, ps
output pulse energy, mJ
two-pass gain coefficient
7,0
LA=3 mm
T=1 ps
T=50 ps
T=100 ps
T=500 ps
LA=53 mm
T=1 ps
T=50 ps
T=100 ps
T=500 ps
Nd:YAG
Wst=12 mJ
rP=rL=0.6 mm
WL=0.6 mJ
Fin/Fsat=8%
Calculations according to
4,5 L.M.Frantz and J.S.Nodvik model,
modified taking into account the
terminal level relaxation

18.

Nd:YAG laser terminal level relaxation time direct
observation
Measurements provide direct diagnostics of the gain
recovery dynamics as a response to a high-power
picosecond pulse saturating the gain medium.
Experimental scheme
etc. scheme
Experimental

19.

Pulse energy in the probe beam channel
The gain is maximum if the test pulse is ahead of the saturating one and drops
sharply when they are coincided.

20.

Experimental results and theoretical modelling
Calculations according to
L.M.Frantz and J.S.Nodvik model,
modified taking into account the
terminal level relaxation
Pulse energy, arb. units
1,0
0,8
0,6
Exp
Prob_with_pump_normalized (ser1)
Prob_with_pump_normalized (ser2)
0,4
0,2
0,0
-400
Based on the time dependence of gain recovery,
the terminal level lifetime can be evaluated as
tTL= 70 ± 15 ps
-200
0
200
400
Delay time, ps
600
800
Sim
W2out 30 ps
W2out 60 ps
W2out 100 ps
W2out 180 ps
W2out 300 ps
1000

21.

Popular Nd-doped laser crystals. Main parameters
Passive mode-locking
t pPML
,min
Active mode-locking
14
4,95
Г
t
gl 0
3,3
M
AML
p
1
F Г
Pulse amplification with saturation effect
Fin
Fout Fs ln 1+ exp
1
exp
s
nl
F
s
Emission
wavelength
λl, nm
Fluoresc
ence
lifetime τ,
µs
Pump
wavelength
λP, nm
Emission
cross
section
σ,
‐19
x10 cm2
Spectral
width
Dn0 /c ,
cm-1
Saturation
fluence Es,
J/cm2
Nd:YAG
1064
230
808
2.8
4.3
0.67
Nd:YLF
π: 1047
σ: 1.053
485
793, 798, 804
π: 1.8
σ: 1.2
13
π: 1.1
σ: 1.6
Nd:YVO
1064
90
808.5
12
11.3
1.5
Laser
induced
damage
threshold
(30 пс)
ELIDT, J/cm2
~1.1*

22.

Conclusions
Such experimental scheme allows direct observation of the
gain recovery dynamics on the transition under investigation
which corresponds to the terminal laser level depopulation
Low level lifetime value of Nd:YAG laser transition 1.064 µm
is estimated as 70±10 ps
Similar study could be reasonable for other neodymium
doped crystalline and glass matrices

23.

Conclusions
Thank you for your attention !