YAG Solid-state Laser Research Articles

Output Characteristics of Q-switched Solid-State Lasers Using Intracavity MEMS Micromirrors

The output behavior of a Nd:YAG solid-state laser actively Q-switched by a MEMS scanning micromirror is presented. Using a gold-coated micromirror, maximum average output powers of 50mW and pulse durations as short as 120ns were obtained with a dual beam output. This output pattern originates from a pulse emission when the micromirror is at an angle from the cavity axis. The temporal and spatial behavior of this laser was experimentally characterized and then modelled using a numerical simulation of the laser rate equations. Finally, prospects for power-scaling this MEMS-based Q-switch technique are demonstrated using a dielectric-coated micromirror, which led to average output powers of up to 650mW and pulse energies above 40μJ.

Analytical investigation of thermal stress in enamel and dentin under CW and pulse Er:YAG solid-state laser

The aim of this work is to evaluate thermal stress of Er:YAG laser radiation on enamel and dentin of the dental. The transient state heat conduction equation for pulse wave laser regime with energy of 100 mJ, 300 mJ and steady state heat conduction equation for CW regime with powers of 1 W, 5 W was solved analytically. Then, the thermally induced stress was investigated following the calculation of the temperature distribution. Using the thermo-mechanical characteristics of the dentin and the enamel, all components of stress were obtained. The thermal stress of Er:YAG laser radiation on the enamel and the dentin calculated in this work may be useful for clinical applications.

Large-energy, narrow-bandwidth laser pulse at 1645 nm in a diode-pumped Er:YAG solid-state laser passively Q-switched by a monolayer graphene saturable absorber

Nonlinear transmission parameters of monolayer graphene at 1645 nm were obtained. Based on the monolayer graphene saturable absorber, a 1532 nm LD pumped 1645 nm passively Q-switched Er:YAG laser was demonstrated. Under the pump power of 20.8 W, a 1645 nm Q-switched pulse with FWHM of 0.13 nm (without the use of etalon) and energy of 13.5 μJ per pulse can be obtained. To the best of our knowledge, this is the highest pulse energy for graphene-based passively Q-switched Er:YAG laseroperating at 1645 nm, suggesting the potentials of graphene materials for high-energy solid-state laser applications.

真空条件下不同波长固体激光烧蚀单晶硅的实验研究

Lasers with wavelengths of 532 nm,355 nm and 266 nm are obtained using harmonic generation of a Nd∶ YAG solid-state laser by nonlinear optical crystal. The relationship between the absorption of single crystal silicon and the laser wavelength and ablation characteristics of single crystal silicon by 3 different wavelength lasers under vacuum condition are studied. The results show that single crystal silicon has a good absorption of ultraviolet laser in the wavelength range of 100- 370 nm,and under the same conditions,the minimum single pulse energy for 532 nm laser ablation of silicon is 30 μJ and the minimum single pulse energy for 355 nm or 266 nm laser ablation of silicon is 15 μJ. The ablation threshold values of 532 nm,355 nm and 266 nm laser ablation of silicon are different,which become smaller with the decrease of wavelength.

Numerical Study of Transient Temperature Distribution in Passively Q-Switched Yb:YAG Solid-State Laser

In this work, the thermal characterization of continuously pumped passively Q-switched laser is quantitatively represented. The system under investigation is end-pumped Yb:YAG passively Q-switched by Cr4+:YAG as saturable absorber. The rate equations describing the dynamics of laser action are numerically solved simultaneously with the temperature conductivity heat equation to depict the transient temperature distribution. The study has been performed in the cylindrical coordinates to characterize the temperature distribution in the axial and radial directions. The thermal transient time in both directions as well as the thermal focal length are calculated. The temporal behavior of the temperature distribution has been illustrated in a 3-dimensional diagram.

99 W mid-IR operation of a ZGP OPO at 25% duty cycle

We have demonstrated the highest reported output power from a mid-IR ZGP OPO. The laser is a cascaded hybrid system consisting of a thulium fibre laser, Ho:YAG solid state laser and a Zinc Germanium Phosphide parametric oscillator. The system produces 27 W of output power in the 3-5 μm wavelength range with an M(2) = 4.0 when operating in a repetitively q-switched mode, and a modulated peak output power of 99 W at a reduced duty cycle of 25%.

Passively Q-switched diode-pumped Er:YAG solid-state laser

We demonstrated laser operation of a passively Q-switched diode-pumped Er:YAG solid-state laser emitting at 1645 or 1617 nm depending on the initial transmission of the Cr:ZnSe saturable absorber. The crystal emitted up to 10 W at 1645 nm and up to 8 W at 1617 nm in CW mode while pumped with 65 W of incident pump power at 1533 nm. In passive Q-switched mode with 40 W of incident power, a Cr:ZnSe saturable absorber with initial transmission of 85% led to 330 μJ pulse energy, 61 ns pulse duration at a repetition rate of 1460 Hz at 1645 nm. An 80% initial transmission Cr:ZnSe sample led to 510 μJ energy pulses, 41 ns pulse duration at a repetition rate of 820 Hz with a central wavelength change from 1645 to 1617 nm. This is the first reported passively Q-switched diode-pumped Er:YAG laser operating on the (4)I(13/2)→(4)I(15/2) transition.

3 μm CW lasers for myringotomy and microsurgery.

This paper describes the development and implementation of 3 μm lasers for myringotomy and microsurgery. Two different lasers were investigated. The first, an Er-doped, CW zirconate glass fiber laser optically pumped by a 970 nm diode laser, emitted > 1 W of CW power at 2.76 μm with concomitant green incoherent emission that served as a convenient visible illumination beam. The second, a 1 W CW Er:YAG solid-state laser also optically pumped by a 970 nm diode laser, emitted > 1 W of CW power at 2.94 μm, coincident with the strongest infrared water absorption peak. Running CW, both lasers are expected to avoid the loud acoustical shocks associated with pulsed lasers. Myringotomies were carried out with the Er:YAG laser on anaesthetized guinea pigs and the effects of the laser were documented. Laser ablated samples of tympanic membrane, soft tissue and bone were histologically examined. Histology results indicated that the CW Er:YAG laser is a potential candidate for a new myringotomy tool and possibly for otologic microsurgery, but deliverable power levels need to be increased to the 2 W (or higher) level. This work was funded under NIH SBIR Grant No. 5R44DC004899.

Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere

Abstract. The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange (68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the new pure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution is 150 m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements, the aerosol extinction coefficient and the aerosol backscatter coefficient at 532 nm can be measured independently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 km height), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratosphere with daylight capability.

Nanosecond pulsed laser micromachining of PMMA-based microfluidic channels

This paper reports an investigation into the effects of nanosecond laser processing parameters on the geometry of microchannels fabricated from polymethylmethacrylate (PMMA). The Nd:YAG solid-state pulsed laser has a wavelength of 1064nm and a measured maximum power of 4.15W. The laser processing parameters are varied in a scanning speed range of 400–800pulses/mm, a pulse frequency range of 5–11Hz, a Q-switch delay time range of 170–180μs. Main effects plots and microchannel images are utilized to identify the effects of the process parameters for improving material removal rate and surface quality simultaneously for laser micromachining of microchannels in PMMA polymer. It is observed that channel width and depth decreased linearly with increasing Q-switch delay time (hence average power) and increased non-linearly with higher scanning rates and not much affected by the increase in pulse frequency.

Laser annealing effect on optical and electrical properties of Al doped ZnO films

Aluminum doped ZnO (AZO) thin films were prepared by RF magnetron sputtering on quartz substrates at room temperature, and then annealed by a Nd:YAG solid-state laser with wavelength 1064nm under different power densities in the air. The characteristics of films were systematically analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectroscopy, spectroellipsometry and Hall measurement at room temperature. The XRD patterns showed that all the films were well crystallized along with c-axial (002). The SEM analysis illustrated obvious grain boundary and non-damage on the surface of films. The grain boundary would result in a decreasing resistivity and a decreasing optical band-gap of the AZO films, which were demonstrated by Hall measurement and UV–vis spectroscopy. The refractive index, the extinction coefficient, and the real and imaginary components of dielectric constant are calculated by spectroellipsometry. The resistivity and transmittance significantly improved when the samples were annealed at 27.8W/mm2.

Study of End Surfaces’ Deformation and Thermal Stress in Solid State Laser

High power solid state lasers have wide applications; they have extensively attracted many attentions. When laser pumped, a lot of heat produces in it causes thermal effects such as stresses end effect and variations of refraction index. In this paper, we analytically study the thermal effects in an Nd: YAG solid state laser crystal which is pumped in longitude with a second order Gaussian (super Gaussian) profile. In this survey we neglect z derivatives of temperature distribution and also consider a statement in which thermal condition of cooler system is much more than thermal condition of laser crystal. Then we apply proper boundary conditions to probe thermal distribution function and related thermal effects. It will be shown that use of second order Gaussian profile for output beam of diode lasers is a better approximation for calculating the thermal distribution and estimating the thermal lensing than the Gaussian profile.

Multi-kW-class 164 μm Er^3+:YAG lasers based on heat-capacity operation

This paper discusses the spectroscopic fundametals, the scaling properties and experimental results of quasi-three-level resonantly diode-pumped Er3+:YAG solid-state heat-capacity laser (SSHCL) technology. With an output power of 4650 W and output energies in excess of 440 J this laser is currently the most powerful ”eye-safe” SSHCL. Due to a moderate crystal temperature rise of only 56.7 K/s at 11.3 kW of pump power and a temperature-related power drop of 8.8 W/K the laser shows strong potential for further upscaling.

Design and construction of a 110 W green laser for medical application

In this paper, the design and the construction of a high-power side-diode-pumped Nd:YAG solid-state laser at repetition rates of 6 and 10 kHz has been presented. Second harmonic of the Nd:YAG laser with green light at 532 nm, with an average power of 111.5 W at 10 kHz repetition rate, and with 90 ns pulse duration, has been obtained by the nonlinear crystal of KTP with 59% conversion efficiency and 12% diode-to-green optical–optical efficiency in the linear resonator. Beam spot size and divergence is 4 mm and 8 mrad, respectively. The laser stability is about 97%. As a medical application of this laser, investigation of degree of effectiveness and penetration depth of laser on adenomas of resected prostate after open prostatectomy has been done.

High-efficiency multi-kilowatt Er^3+:YAGsolid-state heat-capacity laser

First results on a diode-pumped multikilowatt-class Er(3+):YAG solid-state heat-capacity laser (SSHCL) are reported. The laser achieves an output power of 4650 W and output energies in excess of 440 J. A moderate crystal temperature increase due to crystal heating of 56.7 K/s is measured at 11.3 kW of pump power and the temperature-related power drop is determined to 8.8 W/K. The presented work is believed to be the first multi-kilowatt-class resonantly diode-pumped Er(3+):YAG laser.

Effects of laser-induced recovery process on conductive property of SnO2:F thin films

In this study, we developed a laser annealing process to enhance the electrical properties of SnO2:F (FTO) films. It is already known that in contrast to indium oxides or zinc oxides, the carrier mobility of FTO films is relatively lower. Thus, improving the mobility is a direct way to enhance the conductivity of FTO films. Furthermore, improving the crystal quality of the thin films is in turn a direct way to enhance the mobility effectively. Contrary to the high working temperatures of traditional annealing processes, the laser annealing process, with its focusing character, enables us to modify the crystal quality of oxide films on substrates with low-melting points. Using a self-built laser system, which consists of a Nd:YAG solid-state laser with a wavelength of 1064 nm and a beam shaper lens, we carried out a series of experiments to achieve the optimal laser annealing process. Hall, SEM, and XRD measurements were used to characterize the opto-electrical as well as the structural properties. As experimental results show, the tin oxide crystallites recovered well during the laser annealing process. By using a suitable beam profile and a proper laser intensity, the film resistivity was reduced from 7.19 ± 0.55 × 10−3 Ω cm to 6.70 ± 0.20 × 10−3 Ω cm while the carrier mobility was enhanced from 11.18 ± 0.29 cm2/V s to 11.71 ± 0.34 cm2/V s.

Fast and stable enhancement of the far-field peak power by use of an intracavity deformable mirror

We demonstrate that an intracavity deformable mirror (DM) is capable of compensating for the aberrations of a continuous-wave (CW) Nd:YAG solid-state laser and improving its far-field peak power fast and stably. The deformable mirror is controlled by a stochastic parallel gradient descend (SPGD) algorithm. Experimental results reveal that high-order-like transverse modes can be transformed into Gaussian-like modes quickly without any pinhole added in the laser cavity. At the same time, the far-field peak powers are also increased to different extents.

A high power hybrid mid-IR laser source

An efficient hybrid mid-IR laser system comprising a thulium fibre laser, Ho:YAG solid state laser and a zinc germanium phosphide optical parametric oscillator is presented. A 790 nm diode pumped 1908 nm thulium fibre laser operating at 30 W pumps an RTP q-switched Ho:YAG laser emitting 17 W at 40 kHz and 2090 nm. The zinc germanium phosphide optical parametric oscillator efficiently converts this into the 3–5 μm region producing 10.1 W with 59% optical conversion efficiency and an M 2 = 1.5.

Automatic laser beam characterization of monolithic Nd:YAG nonplanar ring lasers

A detailed beam characterization of continuous-wave single-frequency Nd:YAG solid-state ring lasers at a wavelength of 1064 nm is presented. The power noise, frequency noise, beam pointing fluctuations, spatial beam quality, and other properties of eight lasers of the same model were measured with a compact diagnostic instrument based on an optical ring resonator. One of the eight lasers was automatically characterized over a period of 3.5 months to investigate the long-term behavior. The results show that these lasers are highly stable laser sources, that the variations between different samples are rather small, and that these lasers are ideally suited for high precision optical experiments.

First investigations on an Er3+:YAG SSHCL

First results on a diode-pumped Er3+:YAG solid-state heat-capacity laser (SSHCL) are reported. The laser achieves an output power of >70 W and could be operated for >2 s, currently limited by the available pump power with respect to the temperature dependent threshold. The experimental results are in good agreement with the spectroscopically expected performance, predicting high-power kW-class operability of an Er3+:YAG SSHCL. The presented work is believed to be the first Er3+:YAG SSHCL investigated.