LD泵浦Cr4+∶YAG被动调Q锁模Nd∶Gd0.42Y0.58VO4激光器

理论和实验研究了LD泵浦Nd∶Gd0.42Y0.58VO4/Cr4+∶YAG被动调Q锁模激光器.在分析Cr4+∶YAG晶体能级结构和调Q锁模物理过程的基础上,通过数值模拟给出了Cr4+∶YAG调Q锁模的参量要求,然后进行了实验验证.实验中Cr4+∶YAG的初始透过率T0分别为86.3%、95%,输出镜的透过率T分别为10%、20%,在其他条件不变的情况下构成四种不同的组合,均实现了激光器的调Q锁模运转.实验结果表明,降低Cr4+∶YAG的初始透过率T0或提高输出镜透过率T有利于获得较好的锁模效果,与理论分析一致.     

Diode-pumped passively Q-switched and Q-switch mode-locked Nd:YVO<Subscript>4</Subscript> laser using single-wall carbon nanotube based saturable absorber

We present the performance of diode end-pumped Nd:YVO₄ laser in Q-switched and Q-switched mode-locking oscillation using a single-walled carbon nanotube based saturable absorber, which was fabricated using similar vertical evaporation technique. The average output power, repetition rate and pulse width of the Q-switched laser output were studied with different output couplers. The maximum average output power was 130 mW. For Q-switched mode-locking operation, the repetition rate of the mode-locked pulses concentrated in the Q-switched envelope was 58 MHz. The repetition rate of the Q-switched envelope maintained at 18 kHz, while the pulse width decreased along with the increasing of pump power. The maximum average output power was 53 mW.     

Q-switched mode-locking femtosecond all-fiber laser based on Er3+/Yb3+ codoped phosphate fiber

A Q-switched mode-locking femtosecond all-fiber laser based on a 2 cm long homemade Er³⁺/Yb³⁺ codoped phosphate glass fiber has been reported. By using the nonlinear polarization evolution technique, a nearly 100% modulation depth of mode-locking pulse train is achieved. At a pump power of 410 mW, the energy of each Q-switched envelope, whose width is about 220 μs, is 10 μJ, while the duration of mode-locking pulse within the Q-switched envelope is 318-fs.     

Stable passively Q-switched operation of Tm3+ doped silica fiber laser by anti-resonant Fabry-Perot saturable absorber

We demonstrate a diode-pumped passively Q-switched Tm-doped double-cladding silica fiber laser operating at wavelength of 1960 nm using an anti-resonant Fabry-Perot saturable absorber as passive modulation element. To determine a relatively preferable fiber length for stable cw Q-switched operation, three active fiber simples with the length of 1.1, 5.3, and 7.0 m were employed respectively in our experiments. With 1.1 m gain fiber, we generated Q-switched pulses with a pulse width of 245 ns and an average power of up to 2.2 W at a repetition rate of 620 kHz. For the longer two fiber samples, Q-switched operation with longer pulse duration, Q-switched mode-locking and cw mode-locking were observed, respectively.     

A diode-pumped high power Q-switched and self-mode-locked Nd:YVO4 laser with a LiF:F2- saturable absorber

Simultaneous mode-locking and Q-switching has been accomplished in a diode-pumped Nd:YVO₄/LiF:F₂ ^- laser. At an absorbed pump power of 23.6 W, the average output power was 6.0 W and the repetition rate of the Q-switched pulse was 260 kHz. A depth of mode-locking of 100% was obtained and there was no satellite pulse between mode-locked pulse trains. The mode-locked pulse inside the Q-switched pulse had a repetition rate of approximately 148 MHz and its average duration was estimated to be around 75 ps. Received: 6 February 2001 / Revised version: 23 April 2001 / Published online: 18 July 2001     

Diode-pumped simultaneously Q-switched and mode-locked Nd:GdVO<Subscript>4</Subscript>/LBO red Laser

A diode-end-pumped simultaneously Q-switched and mode-locked intracavity frequency doubled Nd:GdVO₄/LBO red laser with an acousto-optic Q-switch was realized. The maximum red laser output power of 250 mW was obtained at the incident pump power of 8.3 W and the repetition rate of 10 kHz. At 5 kHz, the maximum mode-locking modulation depth of about 80% was achieved with the Q-switched pulse width of 440 ns. The red mode-locked pulse inside the Q-switched pulse had a repetition rate of 115 MHz, its average pulse width was estimated to be about 350 ps.     

Theoretical and experimental study of single mode-locking pulse generation with low repetition rate in a dual-loss-modulated QML YVO4/Nd:YVO4 laser with EO and GaAs

Using electro-optic (EO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/Nd:YVO₄ laser at 1.06 μm is realized. The experimental results show that the number of the mode-locking pulses underneath the Q-switched envelope decreased with increasing pump power. With an output coupling of 6.5 %, the single mode-locking pulse underneath the Q-switched envelope with 1 kHz repetition rate was obtained when the pump power exceeded 4.65 W. At a pump power of 8.25 W for an output coupling of 10 %, a stable mode-locking pulse train at a repetition rate of 1 kHz was achieved with pulse energy as high as 582 μJ and pulse duration of about 580 ps, corresponding to a peak power of 1 MW. Using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled rate equations for diode-pumped doubly QML YVO₄/Nd:YVO₄ laser are given and the numerical solutions of the equations are basically in accordance with the experimental results.     

Performance of 2 μm Tm:YAP pulse laser based on a carbon nanotube absorber

We demonstrated the first use of carbon nanotube as a saturable absorber in the Q-switched and Q-switched mode-locking of a diode pumped Tm:YAP operating at 2 μm. At the incident pump power of 8.64 W, the minimum Q-switched pulse width of 255.1 ns, and the maximum peak power 53.1 W can be obtained with the corresponding repetition rate of 21.76 kHz. The performance of a diode-pumped passively Q-switched mode-locked Tm:YAP laser with high repetition rate formed with a folded cavity. As high as 780 mW average output power was produced in QML laser. The repetition rate of the mode-locked pulse inside the Q-switched envelope was 244.1 MHz. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Diode-pumped passively Q-switched mode-locked Nd:YLF laser with uncoated GaAs saturable absorber

We have demonstrated passively Q-switched mode-locked all-solid-state Nd:YLF laser with an uncoated GaAs wafer as saturable absorber and output mirror simultaneously. Q-switched mode-locking pulses laser with about 100% modulation depth were obtained. The average output power is 890 mW at the incident pump power of 5.76 W, corresponding to an optical slop efficiency of 20%. The temporal duration of mode-locked pulses was about 21 ps. At the Q-switched repetition rate of 30 kHz, the energy and peak power of a single pulse near the maximum of the Q-switched envelope was estimated to be about 1.6 μJ and 76 kW.     

Comparative study of the mode-locking of Nd:GdVO_4 and Nd:YAG lasers with semiconductor saturable absorber mirrors

Stable continuous-wave passive mode-locking of diode-end-pumped Nd:GdVO4 and Nd:YAG lasers with semiconductor saturable absorber mirrors (SESAMs) are reported. The comparative study shows that the Nd:GdVO4 crystal is efficient to decrease the Q-switched mode-locking tendency, and easier to continuous-wave (CW) mode lock than Nd:YAG.     

Switchable mode-locking states in an all-fiber all-normal-dispersion ytterbium-doped laser

Multi-operation state in an all-normal-dispersion ytterbium-doped fiber laser is obtained by introducing nonlinear polarization or hybrid mode-locking mechanism in the laser cavity. In addition to operating the laser at continuous-wave mode-locking, various operation states including continuous-wave, Q-switched mode-locking, pulse-splitting, and harmonic mode-locking can be achieved by tuning the laser pump power or an intracavity polarization controller. Insertion of a semiconductor saturable absorber mirror in the cavity helps to shorten the output pulsewidth of the hybrid mode-locked laser. When the pump power is rapidly adjusted, a strong asymmetric hysteresis behavior can be observed during the manipulation between different orders of harmonic mode-locking.     

The acousto-optic Q-switched mode-locking Nd:YVO4 laser

Q-switched mode locking (QML) has been observed in acousto-optic Q-switched Nd:YVO₄ laser that contained no mode-locking components. It was found that QML was easily realized in a long cavity and the modulation depth was observed to increase with increased cavity length. The maximum modulation depth was as high as 90%. This phenomenon is explained by the introduction of gain-related effect in the gain medium. The longitudinal modes at higher frequency, than the central frequency of the gain profile, experience positive guiding, which results in mode locking of these modes.     

Diode-pumped passively Q-switched and mode-locked Nd:GGG laser at 1.3 μm with V<Superscript>3+</Superscript>:YAG saturable absorber

Using V³⁺:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3 μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps.     

High power diode-pumped passively Q-switched and mode-locking Nd:GdVO4 laser at 912 nm

A high power diode-end-pumped passively Q-switched and mode-locking (QML) Nd:GdVO₄ laser at 912 nm was demonstrated for the first time, to the best of our knowledge. A Z-type laser cavity with Cr⁴⁺:YAG crystals as the intracavity saturable absorber were employed in the experiments. Influence of the initial transmission (T_U) of the saturable absorber on the QML laser performance was investigated. Using the T_U = 95% Cr⁴⁺:YAG, as much as an average output power of 2.0 W pulsed 912 nm laser was produced at an absorbed pump power of 25.0 W, then the repetition rates of the Q-switched envelope and the mode-locking pulse were ~ 224 kHz and ~ 160 MHz, respectively. Whereas the maximum output power was reduced to 1.3 W using the T_U = 90% Cr⁴⁺:YAG, we obtained a 100% modulation depth for the mode-locking pulses inside the Q-switched envelope.     

Passive stabilization of a passively mode-locked Nd:GdVO4 laser by inverse saturable absorption

A diode-pumped Nd:GdVO₄ laser mode-locked by a semiconductor saturable absorber and output coupler (SESAOC) is passively stabilized to suppress Q-switched mode-locking. A phase mismatched BIBO second-harmonic generation (SHG) crystal is used for passive stabilization. The continuous wave mode-locking (CWML) threshold is reduced and the pulse width is compressed. The pulse width is 6.5 ps as measured at the repetition rate of 128 MHz.     

Broad spectral pulse operation of 2 μm Tm:YAP laser based on reflection-type carbon nanotube absorber

We demonstrated the first use of reflection-type single-walled carbon nanotube (RSWCNT) as a saturable absorber in the Q-switched mode-locking (QML) of a diode pumped Tm:YAP operating at 2 μm. The spectrum of the QML laser is centered at 1.97 μm with a broad spectral region of 36 nm. At the incident pump power of 10.33 W, as high as 432 mW average output power was produced in QML laser. The repetition rate of the mode-locked pulse inside the Q-switched envelope was 158 MHz. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Q-switched and mode-locked diode-pumped Nd:YAG laser with an LT-GaAs

Simultaneous Q-switching and mode-locking (QML) is accomplished in a diode-pumped Nd:YAG laser using low-temperature GaAs (LT-GaAs) as the saturable absorber, which also acts as an output coupler at the same time. The repetition rate of the Q-switched envelope increased from 25 to 40 kHz as the pump power increased from 2.2 to 6.9 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of 714 MHz. A maximum average output power of 770 mW was obtained.     

High-power passively Q-switched mode-locking Nd:GdVO4 laser with LT-InGaAs saturable absorber

The generation of passively Q-switched mode-locking (QML) pulse has been obtained from a diode-pumped Nd:GdVO₄ laser with a LT-InGaAs wafer as saturable absorber as well as output coupler. Under the incident pump power of 10 W, an average output power of QML was 1.8 W with a Q-switched repetition rate of 280 kHz. The pulse duration of Q-switched pulse is about 160 ns and mode-locked pulse within the Q-switched envelope had a repetition rate of 410 MHz. It is indicated that the present LT-InGaAs is a very promising device in the field of mode locking solid-state laser, and we are sure that it will be complete pure cw mode locking with single beam output easily after further optimizing in the parameter such as saturation fluence, modulation depth, recovery time and damage threshold in semiconductors.     

Experimental Study of a Pulsed Ytterbium-Doped Fibre Laser with Fast and Slow Saturable Absorbers in a Linear Cavity

We present a linear-cavity stretched-pulse fibre laser and by semiconductor saturable-absorber mirrors. A with mode locking by a nonlinear polarization rotation Q-switched mode-locking cw train and a mode-locking pulse train are obtained in the experiment. We investigate the effects of the equivalent fast saturable absorber and the slow saturable absorbers in experiment. It is found that neither the nonlinear polarization evolution effect nor a semiconductor saturable absorber mirror is enough to produce the stable cw mode-locking pulses in this experiment. A nonlinear polarization evolution effect controls the cavity loss to literally carve the pulses; semiconductor saturable absorber mirrors provide the self-restarting and maintain the stability of the modelocking operation.     

Single-walled carbon nanotubes on side polished fiber as a universal saturable absorber for various laser output states

We demonstrated four different laser operational states in the same passive fiber ring laser cavity by controlling solely the polarization state in a saturable absorber. The demonstrated laser operational states were continuous wave, mode-locking, Q-switching, and Q-switched mode-locking. The saturable absorber was fabricated by spin-coating a single-walled carbon nanotubes (SWCNT)/polymer composite on a side polished fiber providing enhanced nonlinear interaction with the SWCNT. The wide tuning range of the saturable absorber allows the simple means to generate different forms of laser output from a single laser cavity.