*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. *E-mail: mdwei@mail.ncku.edu.tw

Outline Dual-wavelength laser Past study of our Lab Laser Phys. 21, 1039-1041 (2011) T-type cavity design Cavity loss modulator – EO PPLN Bragg modulator Optical bistability – Hysteresis loop Pattern formation Summary

Dual-wavelength laser Simultaneously emit dual-wavelength: Nd:YAlO3, Nd:YVO4, Nd:GdVO4, Nd:YAG, Nd:LuVO4......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, 475-478 (2000). 2.Cavity loss IEEE J. Sel. Top. Quant. Electr. 23, 605-612 (1987). Optical bistability : (1064 nm only) Resonator configuration Opt. Lett. 10, 232-234 (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, 545-548 (2006). Er-doped laser: nonlinear saturable absorption IEEE Photonic. Tech. L. 14, 1252-1254 (2002).

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, 1039-1041 (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)

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, S1&S2:AR@1000-1450nm PPLN: AR@1064 , QPM period(μm) 20.3/25.74 M1: HT@808nm, HR@1064&1342nm, PL OC1: PR@1342nm, R=99%, rc1=200 (mm) OC2: PR@1064nm, R=90%, rc2=150 (mm) B.S.: HT@1342nm, HR@1064nm

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

Intracavity Transmission The transmission of EO PPLN versus drive voltage at m = 0. The half-wave voltage of EO PPLN is about 507.9 V

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)

Hysteresis loop & pattern Horizontal Vertical Horizontal Vertical

Hysteresis loop V.S. pump power

Width of Hysteresis loop TL TH

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.

1064nm pattern with polarization 30 40 60 90 120 140 150 180

1342nm pattern with polarization 10 20 30 40 60 50 70 80 90 100 110 120 130 140 150 160 170 180