Pulse train and dual-wavelength dynamics depended on mode competitions in Neodymium-doped solid-state lasers

Abstract

The dual-wavelength Neodymium-doped laser with mode competition and pulse train behavior has been investigated Dual wavelengths at 1 06 ?m and 1 34 ?m corresponding to two transitions of 4F3/2→4I11/2 and F3/2→4I13/2 have been implemented simultaneously emissions in a single laser gain medium on a T-type cavity configuration which was able to independently control the cavity parameters of single laser wavelength for balancing the competition In dual-wavelength pulsed laser a method for generating a dual-wavelength dual pulse Nd:GdVO4 laser at 1 06 ?m and 1 34 ?m is proposed When the 1 34-?m spiking threshold is less than the 1 06-?m Q-switched threshold the generation of a 1 34-?m spiking pulse leads a 1 06 μm Q-switched pulse resulting in a dual-wavelength laser With a pump power of 11 W the pulse widths are 89 5 and 427 8 ns for 1 06 and 1 34 μm respectively with a 36 5-KHz repetition frequency To analyze modes competition in dual-wavelength and bipolarized laser we experimentally demonstrate polarization bistability in a dual-wavelength Nd:YVO4 laser at 1 06 μm and 1 34-?m by using an intra-cavity electro-optic periodically poled lithium niobate (EO PPLN) Bragg modulator to control the loss at 1064 nm An inverse hysteresis switch was observed between 1064 nm and 1342 nm lasers with orthogonal polarizations by increasing and reducing the loss induced by the EO PPLN The size of the hysteresis increased with increasing pump power This dissertation provides an explanation based on cross-gain saturation for the bistable behavior of polarization Moreover the mode competition between ordinary and extraordinary rays can be reduced into single mode oscillation to further generate a cylindrical vector beam based on the optical path difference in birefringence laser crystal when the system was operated in the edge of laser stable region We have proposed a mode-locked Nd-vanadate laser with azimuthal polarization with a semiconductor saturable absorber mirror On the basis of the birefringence of the laser crystal inducing different equivalent lengths for ordinary and extraordinary rays beams were azimuthally polarized around the edge of a stable cavity region In Q-switched mode-locking with cavity length approximate 32 cm at a pump power of 9 W the repetition rate and width for the Q-switched envelope were 318 kHz and 0 91 μs and the mode-locked pulse repetition rate and pulse width were 455 MHz and 65 ps respectively The degree of polarization was controllable up to 95 4 ± 1 4% In continuous wave mode-locking with cavity length approximate 118 5 cm the repetition rate and pulse width for the continuous-wave mode-locked pulse were 125 MHz and 77 ps respectively at a pump power of 11 W The degree of polarization was 90 0% ± 1 9% Comparing to the method based on the thermal induced birefringence the continuous wave mode-locked threshold in our study was sufficiently less than that in the previous studies with about the one-tenth ratio

Date of Award	2016 Jun 21
Original language	English
Supervisor	Ming-Dar Wei (Supervisor)