Systematic evaluation of a holmium:yttrium-aluminum-garnet laser lithotripsy device with variable pulse peak power and pulse duration

Objective:The Holmium:yttrium-aluminum-garnet(Ho:YAG)laser is the standard lithotrite for ureteroscopy.This paper is to evaluate a Ho:YAG laser with a novel effect function in vitro,which allows a real-time variation of pulse duration and pulse peak power.Methods:Two types of phantom calculi with four degrees of hardness were made for fragmentation and retropulsion experiments.Fragmentation was analysed at 5(0.5 J/10 Hz),10(1 J/10 Hz),and 20(2 J/10 Hz)W in non-floating phantom calculi,retropulsion in an ureteral model at 10(1 J/10 Hz)and 20(2 J/10 Hz)W using floating phantom calculi.The effect function was set to 25%,50%,75%,and 100%of the maximum possible effect function at each power setting.Primary outcomes:fragmentation(mm^3),the distance of retropulsion(cm);
5 measurements for each trial.Results:An increase of the effect feature(25%vs.100%),i.e.,an increase of pulse peak power and decrease of pulse duration,improved Ho:YAG laser fragmentation.This effect was remarkable in soft stone composition,while there was a trend for improved fragmentation with an increase of the effect feature in hard stone composition.Retropulsion increased with increasing effect function,independently of stone composition.The major limitations of the study are the use of artificial stones and the in vitro setup.Conclusion:Changes in pulse duration and pulse peak power may lead to improved stone fragmentation,most prominently in soft stones,but also lead to increased retropulsion.This new effect function may enhance Ho:YAG laser fragmentation when maximum power output is limited or retropulsion is excluded.

Effect of water temperature on pulse duration and energy of stimulated Brillouin scattering

The water temperature has a strong effect on the kinematic viscosity, which is inversely proportional to the phonon lifetime and the gain coefficient. The higher the temperature is, the smaller the kinematic viscosity is, and the larger the phonon lifetime is. At a low pump power and a short focal length, we can derive a single-peak stimulated Brillouin scattering （SBS） pulse. The duration of this single-peak SBS pulse depends mainly on the phonon lifetime of water. With the increase of the water temperature, the duration of such a single-peak SBS pulse will become longer, and the SBS energy will become higher for the gain coefficient, which is related to the phonon lifetime. Therefore, varying the medium temperature can lead to the changes of SBS pulse duration and SBS energy.

Influence of Input Pulse Durations on Properties of Er^(3+)/Yb^(3+) Co-doped DCFA

Based on propagation-rate equations, the influence of different input pulse durations on the properties of Er^3＋/Yb^3＋ co-doped double-clad fiber amplifier at dynamic equilibrium was analyzed. The change characteristic of output power sag with pulse duration and repetition rate was shown. Whether single or multichannel input pulses are amplified, the shorter the input pulse duration is, the smaller the power sags of output pulse will be. At low repetition rate, upper gain values（Gupper） of gain swing are almost the same for different input pulse durations, which tend to the small signal gain, but lower gain value（Glower） of short input pulse is larger than that of long input pulse. At highrepetition rate, lower gain value（Glower） approaches to upper gain value（Glower）.

Neural-network・assisted femtosecond laser pulse duration measurement using two-photon absorption

In this work,a neural network(NN)method is developed for pulse duration inferring for an erbium-doped fiber laser at 1550 nm.Experime nt ally,the interferometric autocorrelation trace is observed clearly with the use of the two-photon absorption(TPA)effect in a GaAs photodiode.The intensity autocorrelation function is curvefitted by the NN with an appropriate performance,and the measuring accuracy is consistent with a commercial autocorrelator.Compared with the Levenberg-Marquardt curve-fitting method,the NN can retrieve the intensity autocorrelation function more stably and has a certain noise reduction ability,simplifying the signal processing for a TPA photodiode-based autocorrelator.

High repetition rate actively mode-locked Er:fiber laser with tunable pulse duration

An actively mode-locked fiber laser with controllable pulse repetition rate and tunable pulse duration is presented,in which an optical delay line(ODL)is used to adjust the cavity length precisely for regulating the repetition rate,and a semiconductor optical amplifier(SOA)is introduced for enabling the pulse duration control.Experimentally,continuous tuning of the repetition rate from 2 GHz to 6 GHz is realized,which is limited by the availability of an even higher repetition rate radiofrequency(RF)source.Specifically,when the repetition rate is fixed at 2.5 GHz,the pulse duration can be tuned from 4 ps to30 ps,which is,to the best of our knowledge,the widest tuning range of pulse duration ever achieved in a gigahertz(GHz)repetition rate actively mode-locked 1.5μm fiber laser oscillator.

Determination of bulk viscosity of liquid water via pulse duration measurements in stimulated Brillouin scattering

We present a method by which to determine the bulk viscosity of water from pulse duration measurements of stimulated Brillouin scattering （SBS）. Beginning from a common model of Brillouin scattering, the bulk viscosity is shown to play an important role in Brillouin linewidth determination. Pulse durations of SBS back-reflected optical pulses are measured over the temperature range of 5-40℃. SBS linewidths are de- termined via Fourier transformation of the time-domain results, and the bulk viscosity of water is measured and derived from the obtained values. Our results show that the proposed method for measurement of pulse durations is an effective approach for determining bulk viscosity. The method can be easily extended to determine bulk viscosities of other Newtonian liquids.

Optimization of highly efficient terahertz generation in lithium niobate driven by Ti:sapphire laser pulses with 30 fs pulse duration

We systematically study the optimization of highly efficient terahertz（THz） generation in lithium niobate（LN）crystal pumped by 800 nm laser pulses with 30 fs pulse duration. At room temperature, we obtain a record optical-to-THz energy conversion efficiency of 0.43% by chirping the pump laser pulses. Our method provides a new technique for producing millijoule THz radiation in LN via optical rectification driven by joule-level Ti：sapphire laser systems, which deliver sub-50-fs pulse durations.

MEASUREMENT AND ANALYSIS OF LASER GENERATED RAYLEIGH AND LAMB WAVES CONSIDERING ITS PULSE DURATION

In this article, laser generated Rayleigh and Lamb waves are studied by taking into account its pulse duration. The physical model and theoretical solution are presented to predict the corresponding waveforms for aluminum samples under the ablation generation regime. The waveforms of the excited Rayleigh and Lamb waves by laser with selected pulse duration were measured by laser interferometer and analyzed theoretically, and the agreement between measurement and analysis is demonstrated for the validation of the theoretical model and solution. The broadening of the Rayleigh wave and the disappearing of high order Lamb wave modes can be found with the increase of the pulse duration by the laser ultrasonic technique.

Pump pulse characteristics of quasi-continuous-wave diode-side-pumped Nd:YAG laser

The influence of pumping laser pulse on the property of quasi-continuous-wave(QCW)diode-side-pumped Nd:YAG laser is investigated theoretically and experimentally.Under remaining a fixed duty cycle,the average output power increases,and the corresponding thermal focal length shorten with the increase of the pump pulse duration,which attributes to the decrease of the ratio of pulse buildup time to the pulse duration.At a pump power of 146 W,the laser output power changes from 65.1 W to 81.2 W when the pulse duration is adjusted from 150μs to 1000μs,confirming a significant enhancement of 24.7%.A laser rate equation model incorporating the amplified spontaneous emission is also utilized and numerically solved,and the simulated results agree well with the experimental data.

Statistical properties of the photoelectron energy spectrum generated by an intense laser pulse and a continuous X-ray

This study shows that the photoelectron energy spectrum generated by an intense laser pulse in the presence of a continuous X-ray has interesting and useful statistical properties. The total photoionization production is linearly propor- tional to the time duration of the laser pulse and the square of the beam size. The spectral double energy-integration is an intrinsic value of the laser-assisted X-ray photoionization, which linearly depends on the laser intensity and which quantita- tively reflects the strengths of the laser-field modulation and the quantum interference between photoelectrons. The spectral energy width also linearly depends on the laser intensity. These linear relationships suggest new methods for the in-situ measurement of laser intensity and pulse duration with high precision.

Dynamic Alignment of D2 Enhanced by Two Few-cycle Pulses

Dynamic alignment of D2 induced by two few-cycle pulses was investigated by solving the time-dependent Schr6dinger equation numerically based on a rigid rotor model. The results show that alignment of D2 can be enhanced by two few-cycle pulses compared with the level achievable by a single few-cycle pulse as long as the time delay between two pulses is chosen properly, and the pulse duration of two lasers plays an important role in the aligning process of D2 molecules.

Measurement and control for a repetitive nanosecond-pulse breakdown experiment in polymer films

In order to perform data acquisition and avoid unwanted over-current damage to the power supply, a convenient and real-time method of experimentally investigating repetitive nanosecond-pulse breakdown in polymer dielectric samples is presented. The measurement-acquisition and control system not only records breakdown voltage and current, and time-to-breakdown duration, but also provides a real-time power-off protection for the power supply. Furthermore, the number of applied pulses can be calculated by the product of the time-to-breakdown duration and repetition rate. When the measured time-to-breakdown duration error is taken into account, the repetition rate of applied nanosecond-pulses should be below 40kHz. In addition, some experimental data on repetitive nanosecond-pulse breakdown of polymer films are presented and discussed.

Numerical exploration of coherent excitation in three-level ladder systems

The technique of stimulated Raman adiabatic passage （STIRAP） is used to transfer potassium atoms from the 22p state to the 21p Rydberg state through the intermediate state 22s. The results show that complete population transfer is related to pulse duration and overlap, and occurs when the pulse duration and overlap have adequate values. At the same time, population trapping is also formed. Complete population transfer can also occurs when the two-photon resonance condition （△s = △p） is met.

Spectral energetic properties of the X-ray-boosted photoionization by an intense few-cycle laser

We report a discovery that an intense few-cycle laser pulse passing through gas leaves a fingerprint of its field en- velope on the photoelectron energy spectrum, which involves continuous X-ray radiations. The spectrum resulting from the photoionization processes includes significant quantum enhancement and interference and exhibits interesting energetic properties. The spectral cut-off energies reflect the strength, time, and interference of the laser field modulation on the photoelectron energy. These energetic properties suggest a new method for precise intense-laser-pulse measurement in situ. The method has the advantages of accuracy, simplicity, speed, and large dynamic ranges （up to many orders of intensity）.

Base Pressure Plays an Important Role for Production of Plasma Blob in Argon Plasma

Magnetic confinement of fusion plasma has a wide range of issues to be addressed. Convective transport of plasma in the scrape-off layer of magnetic confinement devices is an interesting research topic for scientists and engineers. The interest in scrape-off layer convective transport has grown in last two decades because of its effect on plasma interaction with the first wall and divertor. By increasing the particle flux into the far scrape-off layer, blobs negatively affect limiters, radio frequency antennas and the first wall. Increased convective heat transport influences core plasma confinement, at least in L-mode plasmas. Here we have reported blob formation in the absent of external magnetic field. It is observed that at low pressure -0.01 rob, transport seems to be dominated by diffusive process. At pressure 〉 1 mb, we observe convective transport in high speed imaging experiments. The role of background neutrals outside plasma boundary has the befitting answer for this phenomenon. Plasma temperature is the other key player. Another interesting observation is that at diffusive transport regime plasma life time is of the order of voltage pulse duration fed to plasma source, where as at convective transport regime plasma life time is increased appreciably.

Comparison of Nitric Oxide Concentrations in μs-and ns-Atmospheric Pressure Plasmas by UV Absorption Spectroscopy

In this paper,an absorption spectroscopy measurement method was applied on two atmospheric pressure plasma sources to determine their production of nitric oxide.The concentrations are essential for evaluating the plasma sources based on the principle of the Dielectric Barrier Discharge（DBD）for applications in plasma medicine.The described method is based on a setup with an electrodeless discharge lamp filled with a mixture of oxygen and nitrogen.One of the emitted wavelengths is an important resonance wavelength of nitric oxide（λ = 226.2 nm）.By comparing the absorption behaviour at the minimum and maximum of the spectral absorption cross section of nitric oxide around that wavelength,and measuring the change in intensity by the absorbing plasma,the concentration of nitric oxide inside the plasma can be calculated.The produced nitric oxide concentrations depend on the pulse duration and are in the range of 180 ppm to 1400 ppm,so that a distance of about 10 cm to the respiratory tract is enough to conform to the VDI Guideline 2310.

Subcycle electron emission in sequential double ionization by elliptical laser pulses

Using a classical ensemble method, we have investigated sequential double ionization (SDI) of Ar atoms driven by elliptical laser pulses. The results show that the ion momentum distribution of the Ar atoms depends strongly on the pulse duration. As the pulse duration increases, the ion momentum distribution changes from two bands to four bands and then to six bands and finally to an eight-band structure. Back analysis of double ionization trajectories shows that the variation of the band structure originates from pulse duration dependent multiple ionization bursts of the second electron. Our calculations indicate that the subcycle electron emission in the SDI could be more easily accessed by using elliptical laser pulses with a longer wavelength. Moreover, we show that there is good correspondence between the scaled radial momentum and the ionization time.

Study of the heavy ion bunch compression in CSRm

The feasibility of attaining nanosecond pulse length heavy ion beam is studied in the main ring （CSRm） of the Heavy Ion Research Facility in Lanzhou. Such heavy ion beam can be produced by non-adiabatic compression, and it is implemented by a fast rotation in the longitudinal phase space. In this paper, the possible beam parameters during longitudinal bunch compression are studied with the envelope model and Particle in Cell simulation, and the results are compared. The result shows that the short bunch 23SU2S＋ with the pulse duration of about 50 ns at the energy of 200 MeV/u can be obtained which can satisfy the research of high density plasma physics experiment.