1. *E-mail: mdwei@mail.ncku.edu.tw
Department of photonics, National Cheng Kung University
Hysteresis loop and pattern from the dual-wavelength competition in a Nd:YVO4 laser with an intracavity periodically-poled lithium niobate Bragg modulator
K. G. Hong1
S. T. Lin2
M. D. Wei1*
1Department of Photonics, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan. 2Department of Photonics, Feng Chia University, 100, Wenhwa Road, Seatwen, Taichung 407, Taiwan. *

2. Outline Dual-wavelength laser
Past study of our Lab Laser Phys. 21, (2011)
T-type cavity design
Cavity loss modulator – EO PPLN Bragg modulator
Optical bistability – Hysteresis loop
Pattern formation
Summary

3. Dual-wavelength laser
Simultaneously emit dual-wavelength:
Nd:YAlO3, Nd:YVO4, Nd:GdVO4, Nd:YAG, Nd:LuVO et al.
Energy competitive behavior:
4F3/2→4I11/2 : 1064 nm.
4F3/2→4I13/2 : 1342 nm.
Consume populations on the same energy level (4F3/2)
 Instability.
Reduce the competition
1.Adjusting cavity mode Appl. Phys. B 70, (2000).
2.Cavity loss IEEE J. Sel. Top. Quant. Electr. 23, (1987).
Optical bistability : (1064 nm only)
Resonator configuration Opt. Lett. 10, (1985).
4F3/2
4F5/2
4I13/2
4I11/2
4I9/2
808 nm
1064 nm
1342 nm
Nd-doped laser
Yb-doped laser:
Bistablilityinput–output hysteresis loop (1040nm&1537nm)
Residual pump Appl. Phys. B 85, (2006).
Er-doped laser:
nonlinear saturable absorption
IEEE Photonic. Tech. L. 14, (2002).

4. Hsu, C. C., Wu, S. S., Chou, C. C. and Wei, M. D.
Continuous-Wave Simultaneous Dual-Wavelength and Power-Ratio-Tunable Operation at 1064 and 1342 nm in an Nd:LuVO4 Laser
Hsu, C. C., Wu, S. S., Chou, C. C. and Wei, M. D.
Laser Phys. 21, (2011)
T-type laser cavity:
Tuning cavity mode at 1064nm only.
Three mirror configuration.
Make cavity mode varies enormously.
L1064=18.05 (cm)
L1064=16.98 (cm)

5. T-type cavity The EO PPLN is an cavity loss modulator.
F1: 1342nm bandpass filter
F2: 1064nm bandpass filter
Pump spot size at Nd:YVO4: 400 (μm)
Cooling temperature: 18 (℃)
Cavity length:
L1342=116.9 (mm)
L1064=141.8 (mm)
Nd:YVO4: Nd-doped 0.5%, c-cut, 3*3*8mm,
PPLN: , QPM period(μm) 20.3/25.74
M1: PL
OC1: R=99%, rc1=200 (mm)
OC2: R=90%, rc2=150 (mm)
B.S.:

6. EO PPLN Bragg modulator
2 mm Z Y X
20.3 μm
10 mm
15 mm θB x y z
Bragg condition: 2ΛsinθB,m = mλ0/n
m is diffraction order.
Λ=20.3 μm.
For m=1 at 1064 nm , θB=0.7∘ θB
m=0
m=1

7. Intracavity Transmission
The transmission of EO PPLN versus drive voltage at m = 0.
The half-wave voltage of EO PPLN is about V

8. Output slope efficiency
Cavity length: (T-type cavity)
L1064=141.8 (mm)
L1342=116.9 (mm), the strongest position of extracting energy
33.67%
12.29%
25.96%
3.92%
Single emission lights
(intracavity transmission T=89.05%)
Threshold
Pth,1064= 3.0 (W)
Pth,1342= 2.5 (W)
Simultaneous emission lights
(intracavity transmission T=85.75%)
Threshold
Pth,1064= 3.5 (W)
Pth,1342= 2.5 (W)

9. Hysteresis loop & pattern
Horizontal
Vertical
Horizontal
Vertical

10. Hysteresis loop V.S. pump power

11. Width of Hysteresis loopTL TH

12. Summary Nd:YVO4 & EO PPLN Bragg modulator
Slope efficiencies & thresholds based on T-type laser cavity:
1064 nm  25.96%, 3.5 W
1342 nm  3.92%, 2.5 W
The hysteresis loop region of the transmission is from 64.88% to 84.47% with pump power 9W.
The width of the hysteresis loop increased as the pump power increased.
In the hysteresis region, the polarization-dependent pattern appears that the competition of these two wavelengths could be a two-dimensional behavior.

13. 1064nm pattern with polarization30 40 60 90
120
140
150
180

14. 1342nm pattern with polarization10 20 30 40 60 50 70 80 90
100
110
120
130
140
150
160
170
180