Analysis of laser-diode end-pumped intracavity frequency-doubled,passively Q-switched and mode-locked Nd:YVO<Subscript>4</Subscript> laser

Simultaneous Q-switching and mode locking in a laser-diode end-pumped intracavity frequency-doubled Nd:YVO₄/KTP green laser using a Cr⁴⁺:YAG saturable absorber with 81% initial transmission is experimentally demonstrated. At an incident pump power of 6 W, 300 mW of average green power was obtained, which is around four times higher than the cw green power obtained without the Cr⁴⁺:YAG crystal. The repetition rate of the mode-locked green pulses was 400 MHz and the individual mode-locked pulse width was measured to be 500 ps. The repetition rate of the Q-sw itched envelope of the mode-locked pulses was 15 kHz at 6 W of incident pump power. The energy of the mode-locked pulse at the peak of the Q-sw itched envelope was estimated to be 1 J and the peak power was estimated to be 2.4 kW. The measured width and the total energy of the Q-sw itched envelope of the mode-locked pulses was 47 ns and 21 J, respectively, at the maximum incident pump power. An analysis of the system by incorporating a nonlinear loss term due to the intracavity second-harmonic generation to the general recurrence relation for the mode-locked pulses under the Q-sw itched envelope at the fundamental wavelength has been presented. Using a hyperbolic secant square function to model the mode-locked pulse, the temporal shape of a single Q-sw itched pulse at the second-harmonic wavelength has been reconstructed. The theoretical calculations of the pulse parameters like pulse energy, peak power, pulse width and pulse-symmetry factor have shown fairly good agreement with the experimental results. PACS 42.55.Rz; 42.55.Xi; 42.60.By     

Diode-pumped passively Q-switched and mode-locked Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> laser with a GaAs saturable absorber

By using a-cut Nd:Lu_0.15Y_0.85VO₄ mixed crystal as laser gain medium, a diode-pumped passively Q-switched and mode-locked (QML) laser with a GaAs saturable absorber in a Z-type folded cavity is demonstrated for the first time. The Q-switched mode-locked laser pulses with about 90% modulation depth are obtained as long as the pump power reached the oscillation threshold. The repetition rate of the passively Q-switched pulse envelope ranges from 50 to 186 kHz as the pump power increases from 0.915 to 6.520 W. Under an incident pump power of 6.52 W, the QML pulses with the largest average output power of 694 mW, the shortest pulse width of 200 ns and the highest pulse energy of 3.73 μJ are obtained. The mode-locked pulse width inside the Q-switched envelope is estimated to be about 275 ps. The experimental results show that Nd:Lu_0.15Y_0.85VO₄ is a promising mixed crystal for QML laser.     

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.     

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.     

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.     

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 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.     

Passively Q-switched mode-locking in a diode-pumped Nd:LuVO<Subscript>4</Subscript> laser with V:YAG

A passively Q-switched and mode-locked Nd:LuVO₄ laser with V:YAG at 1.34 μm was successfully demonstrated. Comparisons between c-cut and a-cut Nd:LuVO₄ lasers were experimentally made. The maximum average output power of 170 mW, the highest Q-switched pulse energy of 4.5 μJ were obtained in c-cut Nd:LuVO₄ laser. The duration of mode-locked pulse was estimated to be less than 540 ps with repetition rate of 110 MHz.     

880 nm LD pumped passive Q-switched and mode-locked Nd:YVO<Subscript>4</Subscript> laser using a single-walled carbon nanotube saturable absorber

We report a 880 nm LD pumped passive Q-switched and mode-locked Nd:YVO₄ laser using a single-walled carbon nanotube saturable absorber (SWCNT-SA). At the pump power of 7.78 W, the average out-put power of 330 mW of Q-switched and mode-locked laser with optical conversion efficiency of 4.2% was generated. The repetition rate and pulse width of the Q-switched envelope were 33 kHz and 5.6 μs, respectively. The repetition rate and pulse energy of the mode-locked pulse within the Q-switched envelope were 80 MHz and 4.1 nJ, respectively.     

Passively Q-switched and mode-locked diode-pumped Nd:YVO4 laser with LT-GaAs output coupler

We have demonstrated an efficient and compact passively Q-switched and mode-locked (QML) 1064 nm Nd:YVO₄ laser by using a low temperature grown GaAs (LT-GaAs) saturable absorber as well as an output coupler. Stable QML with envelope duration as short as 10 ns and Q-switched repetition rate of 36 kHz was obtained. It is the shortest envelope duration as far as we know, and it is so short that it can be used as Q-switching pulses directly. At 6.9 W of the incident pump power, average output power of 1.24 W was achieved and the corresponding peak power and energy of a single Q-switched pulse were 3.44 kW and 34.4 μJ, respectively. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of 780 MHz.     

Efficient graphene Q switching and mode locking of 1.34 μm neodymium lasers

We demonstrate that few-layered graphene sheets used as a saturable absorber can provide efficient Q-switching and mode-locking modulation in 1.34 μm Nd:GdVO(4) bulk lasers. The minimum Q-switched pulses were 450 ns for 260 mW average power, 43 kHz repetition rate, and 2.5 μJ pulse energy. For the mode-locked laser, an average power of 1.29 W was achieved with 11 ps pulse duration and 13 nJ pulse energy. To our knowledge, this average power is the highest yet obtained from a graphene mode-locked laser, and the corresponding optical-optical efficiency of 23% is the best result among 1.3 μm neodymium mode-locked lasers. The quality factor M(2) of the Q-switched beam was 1.4 and 1.6 in the horizontal and longitudinal planes, respectively, and the M(2) of the mode-locked beam reached 1.1 and 1.0. These results clearly indicate the advantages of few-layered graphene as a saturable absorber.     

Actively mode-locked Tm-Ho:LiYF<Subscript>4</Subscript> and Tm-Ho:BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> lasers

We report on the generation of mode-locking pulse trains with high average output powers from diode-pumped Tm-Ho:LiYF₄ and Tm-Ho:BaY₂F₈ lasers emitting at around 2 μm. The highest output power of 365 mW was obtained with the Tm-Ho:YLF₄ laser, whereas the shortest pulse duration of 120 ps and the widest tunability range of 59 nm was achieved with the Tm-Ho:BaY₂F₈ laser. PACS 42.55.Xi; 42.60.Fc; 42.72.Ai; 42.55.Rz; 42.70.Hj     

Analysis of a laser-diode end-pumped intracavity frequency-doubled passively Q-switched and mode-locked Nd:GdVO<Subscript>4</Subscript>/KTP laser with a semiconductor saturable absorber

A diode-pumped passively Q-switched mode-locked (QML) intracavity frequency-doubled Nd:GdVO₄/KTP green laser with a semiconductor saturable absorber is presented. Nearly 100% modulation depth for the mode-locked green pulses can be achieved at any pump power over 1.92 W. The width of the mode-locked green pulse was estimated to be about 150 ps. The mode-locked pulse interval within the Q-switched envelope of 320 ns and the repetition rate of 97.5 kHz were obtained, at an incident pump power of 4.4 W. The repetition rate of the mode-locked green pulses inside the Q-switched envelope was 140 MHz.     

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     

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.     

High-energy mode-locked all-fiber laser with ultralong resonator

The first experimental results on an all-fiber mode-locked ytterbium laser whose ultralong cavity has a length of 8 km are presented. An increase in the length of the laser cavity at a constant mean power of radiation makes it possible to increase the pulse energy by more than two orders of magnitude to a level of 4 μJ, which is record-high for the pulses generated by a fiber mode-locked master oscillator in the absence of Q-switching. A pulse repetition rate of 37 kHz is the record-low repetition rate for the mode-locked lasers. The numerical simulation of the lasing in the absence of extension fiber yields a possibility of a wide-range variation in the pulse duration due to the tuning of the intracavity polarization controllers. The simulation results are in qualitative agreement with the experimental data.     

Theoretical and experimental studies on the self-Q-switched and mode-locked Nd:GdVO<Subscript>4</Subscript>/KTP green laser

A diode-pumped self-Q-switched and mode-locked intracavity frequency doubled Nd:GdVO₄/KTP green laser is presented. The self mode-locking is self-starting and stable. About 100% modulation depth for the self-mode-locked green pulses has been achieved. We propose a developed rate equation model for self-Q-switched and mode-locked lasers, using the hyperbolic secant function methods and the theory of Kerr-lens mode-locking. This will consider the cascading of second-order nonlinearities of KTP crystal, the third-order nonlinearity of the laser medium, influences of the continuous pump rate, and the stimulated radiation lifetime of the active medium. With the model developed, theoretical calculations are shown to be in good agreement with experimental results. The width of the mode-locked green pulse is estimated to be about 120 ps. PACS 42.60.Fc; 42.60.Gd; 42.65.Hw     

A powerful diode-pumped laser source for micro-machining with ps pulses in the infrared, the visible and the ultraviolet

We report a ps diode-pumped Nd:YVO₄ laser system for micro-machining applications. The system consists of a passively mode-locked oscillator followed by a regenerative amplifier. It provides laser pulses at 1064 nm with a pulse duration of 10.2 ps, a repetition rate of 20 kHz and an average output power of 10.8 W. This average power corresponds to a pulse energy of 0.54 mJ. Second-harmonic generation in LBO and fourth-harmonic generation in BBO provide visible (532-nm) and ultraviolet (266-nm) radiation with pulse energies of 270 J and 75 J, respectively. Amplification in a diode-pumped single-pass Nd:YVO₄ amplifier increases the pulse energy of the fundamental 1064-nm laser pulses to 1 mJ. PACS 42.55.Xi; 42.60.Da; 42.65.Ky; 42.65.Re     

High repetition rate passive Q-switching of diode-pumped Nd:GdVO<Subscript>4</Subscript> laser at 912 nm with V<Superscript>3+</Superscript>:YAG as the saturable absorber

The character of a diode-pumped passively Q-switched Nd:GdVO₄/V³⁺:YAG 912 nm laser was demonstrated for the first time to our knowledge. With an absorbed pump power of 7.4 W, an average output power of 360 mW with a Q-switched pulse width of 328 ns at a pulse repetition rate of 163 kHz was obtained. The Q-switching efficiency was found to be 32.7%. Our work further indicated V³⁺:YAG could be an effective fast passive Q-switch for 0.9 μm radiation.     

LD-pumped passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser at 1342 nm with high initial transmission V:YAG saturable absorber

We have realized, for the first time to our knowledge, the passive Q-switching operation of an LD-pumped Nd:GdVO₄ laser at 1342 nm with V:YAG saturable absorber of initial transmission as high as 96%. This laser is investigated under different transmissions of the output coupler. The dependences of average output power, pulse width, pulse repetition rate, single-pulse energy and peak power on incident pump power are also measured. The shortest pulse width of 80 ns, the maximum single-pulse energy of 19.5 μJ and the highest peak power of 244 W are obtained with the output coupler of T = 15% and the pump power of 7.93 W. We find a special experimental phenomenon that the pulse repetition rate begins to drop after reaching the peak with the increase of the pump power. This phenomenon is analyzed and the theoretical calculations are consistent with the experimental results.