High-power Green Laser Research Articles

Green laser pumped congruently-grown LiTaO[formula omitted] based singly-resonant optical parametric oscillator

We report a continuous wave (cw) singly-resonant, single-frequency optical parametric oscillator (SRO) using 50 mm long congruently-grown 8-mol% MgO doped periodically poled LiTaO3 (MgO:cPPLT). The SRO is pumped by a high-power green laser derived from a near-infrared (NIR) fiber laser source. The SRO is tunable in visible band from 740–755 nm (signal) and mid-infrared (MIR) band from 1810–1930 nm (idler). The MgO:cPPLT crystal is characterized by a strong optical absorption at the pump wavelength and relatively small thermal conductivity which leads to substantial rise in crystal temperature which is spatially confined in the region where the pump is present. This local rise in temperature facilitates longitudinal dephasing by virtue of a large thermo-optic coefficient for MgO:cPPLT crystal and its impact manifests through an early saturation effect in conversion efficiency. The impact of thermo-optic manifestations could be observed in the measurement of spatial beam qualities of the modes.

3.6 W compact all-fiber Pr3+-doped green laser at 521 nm

Green semiconductor lasers are still undeveloped, so high-power green lasers have heavily relied on nonlinear frequency conversion of near-infrared lasers, precluding compact and low-cost green laser systems. Here, we report the first Watt-level all-fiber CW Pr3 + -doped laser operating directly in the green spectral region, addressing the aforementioned difficulties. The compact all-fiber laser consists of a double-clad Pr3 + -doped fluoride fiber, two homemade fiber dichroic mirrors at visible wavelengths, and a 443-nm fiber-pigtailed pump source. Benefitting from > 10 MW / cm2 high damage intensity of our designed fiber dielectric mirror, the green laser can stably deliver 3.62-W of continuous-wave power at ∼ 521 nm with a slope efficiency of 20.9%. To the best of our knowledge, this is the largest output power directly from green fiber lasers, which is one order higher than previously reported. Moreover, these green all-fiber laser designs are optimized by using experiments and numerical simulations. Numerical results are in excellent agreement with our experimental results and show that the optimal gain fiber length, output mirror reflectivity, and doping level should be considered to obtain higher power and efficiency. This work may pave a path toward compact high-power green all-fiber lasers for applications in biomedicine, laser display, underwater detection, and spectroscopy.

Effect of Rosensweig instability in a ferrofluid layer on reflection loss of a high-frequency electromagnetic wave

A ferrofluid layer separates into numerous subscale crests, which is referred to as Rosensweig instability, whose shape and size depend on the field condition and the composition of the ferrofluid. A ferrofluid consisting of nanoscale magnetite particles is also used as an electromagnetic (EM) wave absorption and reflection material. For this study, oil-based and mixture ferrofluid layers that split into various shapes of crests in the presence of an external magnetic field are used to form a protruding structure to reflect and scatter the EM wave and decrease EM radiation energy. For an identical field strength, a mixture ferrofluid layer splits into more crests than an oil-based ferrofluid. A mixture crest shows a less uniform size and shape than the oil-based one. A high-power green laser light is used as a visual EM wave emitting to a crest, which has varying tip angles, and to demonstrate the reflection and scattering. The reflection loss increases as the field strength is increased to create a crest of a smaller tip angle. The reflection loss of an EM wave is significantly affected by the transmitting position on a crest and the shape of a crest. Inter-reflection arises if an EM wave is repeatedly reflected on the surfaces of crests, which contributes to a significant reflection loss. An EM wave incident at an angle of 45° on a crest resulting in a larger area of the inter-reflection zone without specular reflection in a trough gives the most significant reflection loss.

Liquid Velocity Distribution in a Flat Channel with Sudden Expansion

The experimental study of the flow structure behind the sudden expansion of the flat channel is performed. The cross section of the channel is 20×200 mm and the step height is 12 mm. Visualization of the flow structure and measurements by means of particle image velocimetry (PIV) is performed using high power green laser sheet and CCD camera. Liquid velocity profiles are measured by means of laser Doppler anemometry (LDA). Automatic position system is used. The structure of liquid flow distribution evolution behind the sudden channel expansion is shown. The data about pressure drop is presented for different liquid flow rates.

Raman Laser Spectrometer: Application to 12C/13C Isotope Identification in CH4 and CO2 Greenhouse Gases

A compact Raman laser gas spectrometer is developed. It comprises a high-power green laser at 532.123 nm as an excitation source and a specially designed gas cell with an internal volume of less than 0.6 cm3 that can withstand gas pressures up to 100 atm. The resolution of the spectrometer is ~1 cm−1. The Raman spectra of chemically pure isotopically enriched carbon dioxide (12CO2, 13CO2) and methane (12CH4, 13CH4) gases are studied. The expected limit of detection (LOD) is less than 100 ppm for the isotopologues of CO2 and less than 25 ppm for those of CH4 (at a gas pressure of 50 atm.), making the developed spectrometer promising for studying the sources of emissions of greenhouse gases by resolving their isotopologue composition. We also show the suitability of the spectrometer for Raman spectroscopy of human exhalation.

Graphene as reusable substrate for bialkali photocathodes

Bialkali photocathodes, such as cesium potassium antimonide (CsK2Sb), can generate a high-brightness electron beam using a high-power green laser. These photocathode materials have potential applications in advanced accelerators and electron microscopes. It is known that the quantum efficiency (QE) of these photocathodes is affected severely by their substrates; however, reusability of the substrates is not well known. Here, we use graphene, silicon (Si), and molybdenum (Mo) substrates to evaluate the effects of substrates on the QE of redeposited CsK2Sb photocathodes after thermal cleanings. We found that the QE of CsK2Sb photocathodes redeposited on a graphene substrate after thermal cleaning at 500 °C remained largely unchanged. On the other hand, the QE of redeposited photocathodes on Si and Mo substrates after thermal cleaning at the same temperature decreased drastically. We used x-ray photoelectron spectroscopy to quantitatively evaluate the residues of photocathodes after thermal cleaning at 400 °C and 500 °C. We found that Sb, K, and Cs are removed by thermal cleaning at 500 °C for the graphene substrate, but all or the majority of these elements remained on the Si and Mo substrates. The results were consistent with our density functional theory calculations for the case of Si, which we investigated. Furthermore, our angle-resolved photoemission spectroscopy on graphene indicated that its intrinsic electronic structure is preserved after photocathode deposition and thermal cleaning at 500 °C. Hence, we attributed the difference in the amount of photocathode residue to the unique dangling-bond-free surface of inert graphene. Our results provide a foundation for graphene-based reusable substrates for high-QE semiconductor photocathodes.

AB100. Modified techniques and clinical results of high power green laser in the treatment of benign prostatic hyperplasia.

ObjectiveTo investigate the safety and clinical efficacy of high power green laser in the treatment of benign prostatic hyperplasia (BPH).MethodsThirty cases of BPH patients accepted the lateral jet type high power green laser enucleation of prostate leaf drawing block chopped. The time of operation, bleeding volume, hemoglobin (Hb) before and after surgery, indwelling catheter time, perioperative complications, changes of IPSS, Qmax and PVR 1 month after operation were assessed.ResultsAll the operations were successfully. The average operative time was (59+16.1) min, amount of bleeding during operation was (36.3+18.5) mL, catheter time was (35.1+20.6) h. IPSS, Qmax and PVR compared with preoperative were statistically better with statistic significant (P<0.01).ConclusionsHigh power green laser enucleation of prostate leaf drawing block chopped technology is safe and reliable, the effect is satisfied.

High electro-to-optical efficiency 180 W Q-switched 532 nm laser with a pulsewidth of 70 ns

A compact straight cavity with two side-pumped Nd:YAG laser heads and a 90 degrees quartz rotator in between is presented. By intracavity-frequency-doubling with a type II LBO crystal in this cavity, an output power of 180.2 W at 532 nm with a repetition rate of 10 kHz was achieved, corresponding to an electrical-to-optical efficiency of 10.9%. To best of our knowledge, this is the highest electrical-to-optical efficiency of the high power green lasers with above 100 W output power, ever reported. The pulsewidth was 70 ns and the peak power was 257.4 kW. The beam parameter product (beam waist multiplied by half beam divergence angle) was estimated to be 4.2 mm mrad and the power fluctuation over 2.5 hours was calculated to be better than +/- 1.2%.

Continuous-wave single-frequency 532 nm laser source emitting 130 W into the fundamental transversal mode

The nonlinear effect of second-harmonic generation is an efficient way to realize high-power green laser sources. But when scaling up the harmonic power, many setups reported in the literature have been limited by conversion efficiency degradation or the fundamental laser power. Here we report on the generation of 134 W of cw laser light at a wavelength of 532 nm from a fundamental power of 149 W by second-harmonic generation in an external optical resonator comprising a lithium triborate crystal. The external conversion efficiency was 90%. The harmonic light consisted of a single spectral line. At least 97% of it was emitted into the fundamental transversal mode.

LD side-pumped intracavity frequency-doubled high power Nd: YAG green laser based on acousto-optic Q-switch

A highly efficient and high power green laser generated by intracavity frequency doubling of a diode-sidepumped Q-switched Nd: YAG laser has been demonstrated. In the simple L-shaped cavity geometry, the maximum green output power of 28.5 W was obtained with a pulse width of 95 ns at a pulse repetition rate of 10 kHz by using a LBO crystal for frequency doubling, corresponding to a conversion efficiency of 11% from diode pump power to pulse green power. At a pulse repetition rate of 1. kHz, 6.9 mJ of pulse energy, 25 ns of pulse duration and 276 kW of peak power were obtained.

SHG Lasers Over 200 W &amp; Laser Processing Applications

In recent years, the use of all solid-state high power green lasers (more than 100 W) has spread into manufac-turing lines. Especially in liquid crystal display (LCD) industries, high power green lasers are becoming highly sought after for the annealing process of amorphous-silicon (a-Si), instead of conventional eximer lasers, due to lower maintenance costs, higher stability and better results in the crystallization process. Laserfront Technologies, Inc.(LFT) has developed a very stable all solid-state high power green laser using the intra cavity second harmonic generation (SHG) technique of the Nd: YAG laser. Its maximum output power has reached 259W, which is the highest power output using the intra cavity SHG technique currently known in the world. In this paper, we report its features and demonstrate cutting copper, which is well known as being a very difficult metal to cut with infrared lasers due to very high reflectivity.

Magneto-optical recording on Pt/Co and GdFeCo/TbFeCo disks using a green laser

The authors report that the Pt/Co multilayer disk and the GdFeCo/TbFeCo double-layer disk have been investigated for high density magneto-optical recording using a low noise and high power green laser. A high carrier/noise (C/N) ratio of 45 dB at a mark length of 0.4 mu m was obtained for both disks with a track pitch of 0.9 mu m. The results show the possibility of areal densities more than three times higher than those of current ISO standard magneto-optical disks. The system noise, the short noise, and the disk noise were measured experimentally as a function of frequency in order to investigate how to improve the C/N ratio using a green laser. >

Second-Harmonic Generation Green Laser for Higher-Density Optical Disks

A laser-diode-pumped intracavity frequency-doubled Nd:YAG laser (SHG green laser) is an excellent light source for reading out higher-density optical disks because of its shot-noise-limited output and diffraction-limited beam quality. Scaling of the green laser using a bundle of fibers was successfully demonstrated to obtain more than 1 W of output power. By using the high-power green laser, generation of continuous-wave fourth-harmonic ultra-violet light for future ultrahigh-density optical memory was also demonstrated.

Hydrodynamic instability in an ablatively imploded target irradiated by high power green lasers

Time evolution of the ablation front displacement between concave and convex regions of a surface corrugated spherical target was observed by flash x-ray radiography. The results are compared with calculations based on the linearized fluid equation combined with a one-dimensional simulation to describe the ambient fluid motion. In the analysis, perturbation of the fluid is scaled up to kδ∼2π (k is the perturbation wavenumber and δ is the perturbation amplitude) for the acceleration phase with perturbation mode numbers of l=20 and 30. The practical perturbation of the target requires a relaxation time to form the nominal eigenstate of the Rayleigh–Taylor instability, which results in time delay of instability growth onset.

Design of whitelight laser based on cathode fall theory

A method is proposed to design a hollow-cathode type whitelight laser by applying the cathode fall theory. Several design examples and their oscillation characteristics are presented. The concentric-cylinder-type laser tube is found to be suitable for a long life, high power green laser, but some difficulties exist in its use as a white-light laser. The flute-type laser tube, however, appears to be suitable as a whitelight laser.

EFFECTS OF HIGH-POWER GREEN LASER RADIATION ON CELLS IN TISSUE CULTURE.

THE availability of high-power, coherent radiation at new wave-lengths, by means of non-linear optics, has made possible new experiments in the field of radiation effects on cells in tissue culture. It has been shown1,2, by exposure of melanin granules to ruby radiation at 6943 A and its harmonic at 3471 A, that injury sustained by cells in tissue culture is strongly dependent on wave-length. This confirmed the observations by Bessis et al.3 that erythrocytes were destroyed by ruby laser radiation while unstained leucocytes were not affected. Because particular cellular constituents such as pigment granules, haemoglobin and reduced cytochromes b and c show absorption at 5300 A, there was great interest in exploring the radiation effects from the second harmonic output at 5300 A of neodymium (Nd) Q-switched lasers. In the work reported here, a variety of cell types were irradiated with power density at this wave-length in the range of 0.05–100 MW/cm2 to observe their response.