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Speaker : Huang Chi Chung Teacher : Ja-ho Lin

Diode-pumped doubly passively Q-switched Nd:LuVO 4 laser with Cr 4+ :YAG saturable absorber and GaAs output coupler. Speaker : Huang Chi Chung Teacher : Ja-ho Lin. Outline. Introduction Experimental arrangement Experimental results Conclusions. Introduction.

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Speaker : Huang Chi Chung Teacher : Ja-ho Lin

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  1. Diode-pumped doubly passively Q-switched Nd:LuVO4 laser with Cr4+:YAG saturable absorber and GaAs output coupler Speaker : Huang Chi Chung Teacher : Ja-ho Lin

  2. Outline Introduction Experimental arrangement Experimental results Conclusions

  3. Introduction The advantages of diode-pumped passively Q-switched lasers Inherent simplicity Good frequency stability High efficiency High peak power Nd-doped vanadate laser crystal, Such as Nd:YVO4 ,Nd:GdVo4 High thermal conductivity Large absorption and Stimulated emission cross sections Nd-LuVO4 (It has attracted attention recently) Has excellent thermal property 7.882 (W/m/K) at [100]direction(a-cut) 9.629 (W/m/K) at [001]direction(c-cut) k: the thermal conductivity A : the total cross sectional area of conducting surface ΔT: temperature difference x : the thickness of conducting surface

  4. Passive Q-switched techniques are simple and convenient require minimum optical element no external driving devices depend on availability of saturable absorbers Such as Cr4+:YAG, Cr4+:Mg2SiO2, Cr4+:YSO, GaAs The advantage of Cr4+:YAG high damge threshold large thermal conductivity The advantage of GaAs thermal stabilities large optical nonlinearity which is related to the two-photon absorption The uncoated GaAs can be used as not only a saturable absorber but also an output coupler The passively double Q-switches using the both Cr4+:YAG and GaAs saturable absorber can obtain a symmetric pulse shape in comparison with single saturable absorber .

  5. Experiment arrangement M1: a concave mirror (radius of 200 mm) AR-coated at 808 nm on its outside surface HR-coated at 1064 nm on its inside surface. GaAs: the output coupler (580 μm thickness , OC and SA) Cr4+:YAG: saturable absorber (T0= 71% and 81%) a-cut Nd:LuVO4: the gain medium (dimensions: 3×3×2.5 mm3 ) Nd-doping concentration of 0.5 at.%. AR-coated at 808 nm and 1064 nm on one surface AR-coated at 1064 nm on the other surface Cavity length :6.5cm between M1 and GaAs 6.5cm Figure 1

  6. Experiment arrangement The pump source is a fiber-coupled laser-diode (FAP-I system, Coherent Inc.,USA) center wavelength: 808 nm. The diameter of fiber: 800 μm, is focused into the laser crystal with a spot of about 440 μm in diameter at focal plane by a focusing optics. The distance between Cr4+:YAG and GaAs is 1 cm. As an output coupler, GaAs has a transmission of 36.7% at 1.06 μm. The distance between M1 and GaAs is 6.5 cm. The EPM 2000 Energy/Power Meter (Molectron Detector Inc., USA) used to measure the output powers TED 6208 digital oscilloscope (500-MHz bandwidth, Tektronix Inc., USA) are used to measure the pulse widths of the laser.

  7. Experiment results The average output power PAversus incident pump power The pulse width of the pure GaAs Q-switched laser versus incident pump power The pulse repetition rate Fandthe pulse peak powers versus incident pump power The comparison of temporal profiles of single pulse Single-pulse temporal profile

  8. Average output power PA with different T0 The bigger the T0 at a certain incident pump power obtain the higher the average output power. At the incident pump power =11.23 W, the maximum average output power PA At T0 = 0.71 PA= 1.15 W At T0 = 0.81 PA= 1.31 W Slope efficiency at T0=0.71 is 11% at T0=0.81 is 12.2% Incident pump power, W • Fig. 2.

  9. The pulse width of the pure GaAs Q-switched laser At the incident pump power of 11.23W, the shortest pulse width 4.18ns at T0 = 0.71 5.42 ns at T0 = 0.81 At the incident pump power of 12.7 W, An et al. used much short cavity lengthof 4cm and have been obtained the pulse width of 3.8 ns with the peak power of 482 W For the stability of the laser, Doubly passively Q-switched laser can generate the shorter pulse width compared with single GaAs Q-switched laser.

  10. The pulse repetition rate F andthe pulse peak powers versus incident pump power Single-pulse energy Eand peak power P are obtained using the equations E = PA/Fand P =E/W Ddoubly passively Q-switched laser obtains much higher single-pulse peak power than the pure GaAs Q-switched laser.

  11. The comparison of temporal profiles of single pulseat pump power of 9.8 W Fig. (a) reveal the pulse with pure GaAs, Fig.(b) and (c) reveal the doubly passively Q-switched lasers with T0 = 0.81 and T0 = 0.71 With the same incident pump power of 9.8 W, pulse width are 8.85 ns at Fig.(a), 7.34 ns at Fig. (b), 5.72ns at Fig. (c) , Doubly passively Q-switched laser generates much narrower and more symmetric pulse shape than single GaAs Q-switched laser.

  12. Single-pulse temporal profile at pump power of 11.23 W The doublypassivelyQ-switched Nd:LuVO4 laser T0 = 0.81 pulse width= 5.42 ns It is almost absolutely symmetric.

  13. Conclusion We have successfully presented a diode-pumped doubly passively Q-switched Nd:LuVO4 laser with Cr4+:YAG saturable absorber and GaAs output coupler. For the stability of the laser, our doubly passively Q-switched laser has the cavity length of 6.5 cm, can obtain more symmetric pulse shape and higher peak power than single GaAs Q-switched laser. Nd:LuVO4 has been proved a promising gain medium for diode pump doubly passively Q-switched lasers through the experimental results.

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