Growth And Properties Of Nd:CNGG And Nd:CLNGG Disordered Laser Crystals

Diode-pumped solid-state ultrashort pulse lasers have important applications in thefields of controlled nuclear fusion, plasma physics, remote sensing, chemical andphysical dynamics, biology, high speed imaging, optical communications, spectroscopy,holography, nonlinear optics etc. Mode-locking technology is an efficient way to obtainultrashort lasers. The pulse duration is inversely proportional to the oscillationbandwidth by the mode-locking modulation, which is determined by the net gainbandwidth. That is to say, the pulse duration was determined by the gain bandwidth oflaser media. If the laser media have broad gain bandwidth, the short pulses are expected.Although rare earth active ions in glasses possess broad fluorescence spectra, theapplication in high-power or high repetition rate systems is limited by their smallthermal conductivity. Just restricted by the ordered crystal lattice, their fluorescencelines are too narrow to generate ultrashort pulse. Between the two regimes, there is aclass of materials called disordered crystals which have broad absorption and emissionspectra like glasses and excellent thermal properties like single crystals. They are thepromising laser media for high-power and high repetition rate ultrashort laser.Nd:CNGG and Nd:CLNGG laser crystals investigated in this dissertation are twotypical disordered laser crystals. The main contents include:1. The equipment and technology of Nd:CNGG and Nd:CLNGG for growth are introduced. The factors influenced on the crystal quality are also discussed. Large dimension and high quality Nd:CNGG and Nd:CLNGG crystals were successfully grown by the Czochralski method.2. Thermal property of Nd:CLNGG was systematic measured for the first time to our knowledge. It has been found that its thermal conductivity was higher than glasses. The absorption and fluorescence spectra were also measured for both Nd:CNGG and Nd:CLNGG crystals, which showed broader than 10 nm lines. So it has promising application in the ultrashort pulse regime.3. With a laser-diode (LD) as the pump source, continuous-wave(CW) laser performance at 1.33μm of Nd:CNGG and Nd:CLNGG crystals was demonstrated for the first time to our knowledge. The respective maximum powers of 158 mW and 141 mW for Nd:CNGG and Nd:CLNGG lasers were obtained with corresponding optical conversion efficiencies of 1.3% and 1.5%, and slope efficiencies of 2.0% and 2.9%.4. High-power dual-wavelength laser output with disordered Nd:CNGG crystal was demonstrated. CW output power of 4.03 W was obtained with a slope efficiency of 31%. With Cr⁴⁺:YAG as saturable absorber, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 12.9 ns, 173.16μJ, and 12.3 kW in passively Q-switched operations.5. High-power efficient LD pumped Nd:CNGG laser was also demonstrated. A maximum of 3.81 W with a slope efficiency of 30.3% was obtained in the CW laser operation. The passively Q-switched laser has been obtained for the first time to our knowledge. The shortest pulse width, largest pulse energy and highest peak power were determined to be 12.3 ns, 265.3μJ and 20.8 kW with Cr⁴⁺:YAG crystal as saturable absorber.6. With SESAM as saturable absorber, dual-wavelength synchronously mode-locked Nd:CNGG laser was demonstrated with dispersion compensation. The fundamental mode locked pulse train has a repetition rate of 88 MHz and pulse duration of 5 ps, with an average output power of about 90 mW. Autocorrelation measurements show that each of the synchronously mode-locked pulses consists of a train of quasi-periodic beat pulses with a 660 fs pulse width and a 0.63 THz repetition rate.7. The passive mode-locked Nd:CLNGG laser was also demonstrated as same as Nd:CLNGG laser. 900 fs CW mode-locked pulses was generated at the center of 1061 nm wavelength with a maximum average output power of 486 mW and a slope efficiency of 26%.