Largest Pulse Energy Research Articles

Numerical Simulation of the Micro-explosion during Ho:YAG laser lithotripsy

The micro-explosion during Ho:YAG laser lithotripsy may cause calculus fragmentation and migration. It plays an important role to the surgery. A numerical simulation of the micro-explosion during Ho:YAG laser lithotripsy has been developed. The explosion problem in water environment was solved by the Euler algorithm and the piecewise parabolic method (PPM) was selected in the calculation. This simulation investigated the explosion dynamics evolution in the lithotripsy area. The pressure and intensity of the calculus surface were calculated for different laser pulse energy and different distance between calculus and fiber tip. The calculation results indicate that the micro-explosion's properties are determined by the pulse energy, pulse duration and the water distance. Though Short pulse duration and large pulse energy cause high ablation efficiency, it mains more calculus retropulsion at the same time. The ideal surgery results need property laser parameters.

Large Energy Pulse Generation Modulated by Graphene Epitaxially Grown on Silicon Carbide

Graphene grown by thermal decomposition of a two-inch 6H silicon carbide (SiC) wafers surface was used to modulate a large energy pulse laser. Because of its saturable absorbing properties, graphene was used as a passive Q-switcher, and because of its high refractive index the SiC substrate was used as an output coupler. Together they formed a setup where the passively Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal laser was realized with the pulse energy of 159.2 nJ. Our results illustrate the feasibility of using graphene as an inexpensive Q-switcher for solid-state lasers and its promising applications in integrated optics.

Spectral characterization and laser performance of a mixed crystal Nd:(Lu_xY_1-x)_3Al_5O_12

An Nd-doped Lu(1.5)Y(1.5)Al(5)O(12) (Nd:LuYAG) crystal was obtained by Czochralski method. Absorption and emission spectra were recorded at low and room temperature. Continuous wave (CW) and passively Q-switched laser operations of Nd:LuYAG crystal were, to our knowledge, demonstrated for the first time. A CW output power of 1.67 W with slope efficiency of 39.8% was obtained. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 9.6 ns, 61.7µJ, and 6.4 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers.

Starting dynamics of dissipative-soliton fiber laser

We study the starting dynamics of an all-normal-dispersion Yb-doped fiber laser experimentally and compare them to an existing stochastic model of starting from quantum noise. The laser reaches mode locking 10 to 100 times faster than a soliton laser with similar parameters. According to the model, the fast starting can be attributed to the large pulse energy in the normal-dispersion laser. We also report direct observations of starting from relaxation oscillations and discuss that process in light of the theory.

Diode-end-pumped passively Q-switched 133 µm Nd:Gd_3Al_xGa_5-xO_12 laser with V^3+: YAG saturable absorber

We demonstrated the 1.33 microm laser performance with Nd:Gd(3)Al(x)Ga(5-x)O(12) (x = 0.94) (Nd:GAGG) laser crystals for the first time. Continuous-wave (cw) output power of 2.45 W was obtained with the optical-optical conversion efficiency of 21.8% and slope efficiency of 23.3%. In the passive Q-switching regime, the highest output power, the shortest pulse width, largest pulse energy and highest peak power were achieved to be 326 mW 18.2 ns, 36.3 microJ and 2.0 kW, respectively, with V(3+):YAG crystal as the saturable absorber.

Efficient triwavelength laser with a Nd:YGG garnet crystal

We demonstrate a laser-diode pumped efficient triwavelength laser at about 1.06microm with a Nd-doped yttrium gallium garnet crystal for the first time, to our knowledge. Continuous wave output power of 7.15W was achieved under an absorbed pump power of 14.1W, corresponding to the slope efficiency of 52.7%. With Cr:YAG as the saturable absorber, passive Q-switching performance was obtained. The shortest pulse width, largest pulse energy, and highest peak power were obtained at 3.1ns, 153.8microJ, and 46.6kW, respectively. The laser spectrum was found to be a triwavelength, with respective wavelengths of 1062.1, 1060.3, and 1058.9nm, and three laser transitions were assigned.

Pulse Delay Measurements in Cascaded Quantum-Well Gain and Absorber Media

A tunable delay of ultrashort laser pulses in semiconductor waveguide structures are demonstrated in cascaded amplifying and absorbing semiconductor waveguides and compared with a single sectioned waveguide. The single sectioned waveguide shows a low transmission at the maximum delay. This is effectively avoided with the cascaded waveguide configuration, where it is demonstrated viable achieving a net pulse delay while maintaining a transmission of unity. For both types of devices, a pulse advancement is observed, at large pulse energies, that existing models are unable to account for.

A lidar for water vapour measurements in daytime at Lampedusa, Italy

ENEA is planning to develop a lidar system for measurement of the vertical profi le of water vapour mixing ratio in daytime at a remote site, the Station for Climate Observations located in Lampedusa, Italy. The Raman lidar technique has been retained because of its experimental simplicity with respect to DIAL, and the UV spectral range has been chosen because Raman cross-sections and detector effi ciencies are larger. For a wavelength larger than ~ 300 nm the signal is limited in daytime by sky background, but extinction is acceptable, and the aims of the system can be reached with a strong laser source. The 355 nm wavelength of a frequency-tripled Nd:YAG laser has been retained as this laser source permits to reach a large pulse energy while keeping the system simple to operate. Geometrical form factor calculations need to be performed to evaluate the near-range overlap between the laser beam and the fi eld-of-view of the receiver. Among several options, a dual-receiver system has been retained to account for the several orders of magnitude expected in the backscattered signal intensity: a smaller receiver, with a primary mirror of 200 mm diameter for the 0.2-1 km range, and a larger 500 mm receiver for the 1-3 km range.

Passively Q-switched Nd:YAG ceramic laser towards large pulse energy and short pulse width

A large pulse energy and high peak power passively Q-switched ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG) laser has been demonstrated with Cr4+:YAG crystals as the saturable absorbers. By employing a continuous wave (CW) laser-diode (LD) as the pump source, as high as 11.3 W CW output power of 1064 nm was obtained under the pump power of 21.6 W, with an optical conversion efficiency of 52.3%. Inserting different initial transmissions Cr4+:YAG as saturable absorbers, under the incident pump power of 15.6 W, the largest pulse energy, shortest pulse width, and highest peak power are measured to be 188 µJ, 3.16 ns, and 59.5 kW, respectively. As we has known, this is the best passively Q-switched results ever reported by Nd:YAG ceramic material.

A benchtop, ultrafast infrared spectroscopic imaging system for biomedical applications

We discuss the potential biomedical applications for a novel infrared spectroscopic microimaging system. A tunable, table top solid-state laser has been coupled to a commercial infrared microscope, fitted with a modified high resolution infrared camera, to create a unique tool for midinfrared imaging. The system is capable of performing broadband imaging at a diffraction-limited spatial resolution, as is demonstrated here by spatially resolved spectroscopy of polymer test samples with a spectral resolution of 20 cm(-1). The large pulse energies (tens of microjoules) offer previously unobtainable combinations of high signal-to-noise levels and rapid data collection times which are superior to current stand-alone laboratory instruments by many decades. Coupled with the short (100 ps) short pulse duration, these characteristics promise to make a wide range of time-resolved and reflection mode imaging experiments possible with live biological systems.

Continuous-wave and passively Q-switched laser performance with a disordered Nd:CLNGG crystal

We demonstrated efficient high-power continuous-wave (cw) and passively Q-switched disordered Nd:CLNGG laser performance. In cw operations, the output power was obtained to be 3.81 W with a slope efficiency of 30.3%. To our knowledge, they are the highest cw power and efficiency with Nd:CLNGG as the gain medium and a laser-diode (LD) as the pump source. Recorded with a spectrum analyzer, no splitting was found in the Nd:CLNGG laser, which is different with that of its isomorph Nd:CNGG. The LD pumped passively Q-switched Nd:CLNGG laser was obtained for the first time to our knowledge. The shortest pulse width, largest pulse energy and highest peak power were achieved to be 12.3 ns, 199.1 microJ and 16 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers.

Large energy mode locking of an erbium-doped fiber laser with atomic layer graphene

We report on large energy pulse generation in an erbium-doped fiber laser passively mode-locked with atomic layer graphene. Stable mode locked pulses with single pulse energy up to 7.3 nJ and pulse width of 415 fs have been directly generated from the laser. Our results show that atomic layer graphene could be a promising saturable absorber for large energy mode locking.

High-power dual-wavelength laser with disordered Nd:CNGG crystals

We demonstrate the high-power dual-wavelength laser output with disordered Nd:CNGG laser crystals. Continuous-wave output power of 4.03 W was obtained under the incident pump power of 15.62 W. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 12.9 ns, 173.16 microJ, and 12.3 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers. By spectral analysis, the output lasers were found to have dual wavelengths. We believed that the passively Q-switched dual-wavelength laser should be possible to be used as a source for the generation of terahertz radiation.

Giant-chirp oscillators for short-pulse fiber amplifiers.

A new regime of pulse parameters in a normal-dispersion fiber laser is identified. Dissipative solitons exist with remarkably large pulse duration and chirp, along with large pulse energy. A low-repetition-rate oscillator that generates pulses with large and linear chirp can replace the standard oscillator, stretcher, pulse-picker, and preamplifier in a chirped-pulse fiber amplifier. The theoretical properties of such a giant-chirp oscillator are presented. A fiber laser designed to operate in the new regime generates approximately 150 ps pulses at a 3 MHz repetition rate. Amplification of these pulses to 1 microJ energy with pulse duration as short as 670 fs demonstrates the promise of this new approach.

Passively Q-switched laser performance of c-cut Nd:Gd 0.63Y 0.37VO 4 crystal

Passively Q-switched c-cut Nd:Gd 0.63Y 0.37VO 4 laser performance at 1.06 μm was demonstrated with Cr 4+:YAG as saturable absorbers for the first time to our knowledge. This c-cut mixed crystal was found to have large energy storage capacity. The shortest pulse width, largest pulse energy, and highest peak power were obtained to be 6.6 ns, 201.7 μJ, and 30.6 kW, respectively.

Growth and passively self-Q-switched laser output of new Nd^3+,Cr^5+:GdVO_4 crystal

A new passively self-Q-switched Nd, Cr:GdVO(4) laser crystal was grown by Czochralski method for the first time to our knowledge. Polarized absorption spectra were measured at room temperature. The absorption bands display polarization character and an absorption band of Cr(5+) ions at 1110 nm enables the crystal to be a self-Q-switched laser material at 1.06 mum. In the passive self-Q-switching operation, the maximum output power, shortest pulse width, and largest pulse energy were obtained to be 265 mW, 230 ns, and 1.12 microJ, respectively.

Continuous wave and passively Q-switched laser performance of a Nd-doped mixed crystal Nd:Lu0.5Gd0.5VO4

The authors reported continuous wave (cw) and passively Q-switched laser performances of Nd:Lu0.5Gd0.5VO4 crystal at 1.06μm. cw output power of 6.65W was obtained under the incident pump power of 13.75W with slop efficiency of 51%. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 6.2ns, 192.5μJ, and 31.06kW, respectively, with Cr4+ doped yttrium aluminum garnet crystals as the saturable absorbers.

Theoretical investigation of feasibility of Yb:YAG as laser material for nanosecond pulse emission with large energies in the Joule range

The long fluorescence lifetime of the upper laser level of Yb:YAG seems to make it an attractive material for the realization of Q-switched pulses with large pulse energy. The consequences of the spectroscopic parameter set of Yb:YAG for the feasibility of a large pulse energy laser, which emits pulses with nanosecond duration, are addressed on the basis of a rate equation model. The rate equations are analytically solved and applied to the optical side pumping of Yb:YAG rods. The thermal population of the lower laser level and the saturation of the laser material are discussed in specific.

CW and Q-switched laser output of LD-end-pumped 1.06μm c-cut Nd:LuVO_4laser

The continuous-wave (cw) and pulsed laser performances of laser-diode (LD)-end-pumped c-cut Nd:LuVO(4) at 1.06 mum were achieved for the first time. Maximum cw output of 2.35W was obtained. Compared with the cw laser output of a-cut Nd:LuVO(4) crystal, the efficient emission cross-section of the c-cut crystal has been calculated to be 3.24x10(-19)cm(2). The largest pulse repetition rate, shortest pulse width, largest pulse energy and highest peak power were measured to be 20 kHz, 12 ns, 84.93 muJ and 7.02 kW, respectively, by using Cr(4+):YAG crystals as the saturable absorbers in the passive pulsed laser output experiments.

Stress wave emission and cavitation bubble dynamics by nanosecond optical breakdown in a tissue phantom

Stress wave emission and cavitation bubble dynamics after optical breakdown in water and a tissue phantom with Nd: YAG laser pulses of 6 ns duration were investigated both experimentally and numerically to obtain a better understanding of the physical mechanisms involved in plasma-mediated laser surgery. Experimental tools were high-speed photography with 50000 frames s, and acoustic measurements. The tissue phantom consisted of a transparent polyacrylamide (PAA) gel, the elastic properties of which can be controlled by modifying the water content. Breakdown in water produced a purely compressive stress wave. By contrast, in stiff PAA samples and for sufficiently large pulse energies, the compression wave was followed by an intense tensile wave, similar to the behaviour previously observed in cornea. The elastic/plastic response of the medium led to a significant decrease of the maximum size of the cavitation bubble and to a shortening of its oscillation period which was found to be related to the generation of the tensile stress wave upon breakdown. For increasing elastic modulus of the PAA, both the amplitudes of the bubble oscillation and of the stress wave emitted during bubble collapse decreased until the bubble oscillation was so strongly damped that no collapse stress wave was emitted. Numerical simulations were performed using a spherical model of bubble dynamics which includes the compressibility and elastic/plastic behaviour of the medium, viscosity, density and surface tension. The calculations revealed that consideration of the elastic/plastic behaviour of the medium surrounding the bubble is essential to describe the experimentally observed bipolar shape of the stress wave emitted upon optical breakdown. Water is a poor tissue model because the shape of the emitted stress waves and the bubble dynamics differ strongly for both materials. The mechanical properties of PAA were also found to be quite different from those of tissues. Experimental and numerical results provided evidence that the dynamic mechanical properties relevant for optical breakdown in PAA and tissue differ by as much as two orders of magnitude from the static values. The discovery of a tensile stress wave after optical breakdown in tissue-like media is of great importance for the assessment of collateral damage in laser surgery because biological tissues are much more susceptible to tensile stress than to compressive stress.