Two-micron （thulium） laser resection of the prostate- tangerine technique： a new method for BPH treatment

Two-micron （thulium） laser resection of the prostate-tangerine technique （TmLRP-TT） is a transurethral procedure that uses a thulium laser fiber to dissect whole prostatic lobes off the surgical capsule, similar to peeling a tangerine. We recently reported the primary results. Here we introduce this procedure in detail. A 70-W, 2-um （thulium） laser was used in continuous-wave mode. We joined the incision by making a transverse cut from the level of the verumontanum to the bladder neck, making the resection sufficiently deep to reach the surgical capsule, and resected the prostate into small pieces, just like peeling a tangerine. As we resected the prostate, the pieces were vaporized, sufficiently small to be evacuated through the reseetoscope sheath, and the use of the mechanical tissue morcellator was not required. The excellent hemostasis of the thulium laser ensured the safety of TmLRP-TT. No patient required blood transfusion. Saline irrigation was used intraoperatively, and no case of transurethral resection syndrome was observed. The bladder outlet obstruction had clearly resolved after catheter removal in all cases. We designed the tangerine technique and proved it to be the most suitable procedure for the use of thulium laser in the treatment of benign prostatic hyperplasia （BPH）. This procedure, which takes less operative time than standard techniques, is safe and combines efficient cutting and rapid organic vaporization, thereby showing the great superiority of the thulium fiber laser in the treatment of BPH. It has been proven to be as safe and efficient as transurethral resection of the prostate （TURP） during the 1-year follow-up.

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold（LIDT） of the mitigated site is tested using 355 nm laser beam with a small spot（0.23 mm 2） and a large spot（3.14 mm 2）,separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.

Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

Photoacoustic imaging,an emerging biomedical imaging modality,holds great promise for preclinical and clinical researches.It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission.In order to generate photoacoustic signal e±-ciently,bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization.As an alternative,the miniaturized semiconductor laser system has the advantages of being inexpensive,compact,and robust,which makes a signi¯cant e®ect on production-forming design.It is also desirable to obtain a wavelength in a wide range from visible to nearinfrared spectrum for multispectral applications.Focussing on practical aspect,this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

Design of NO2 photoacoustic sensor with high reflective mirror based on low power blue diode laser

An NO2 photoacoustic sensor system with a high reflective mirror based on a low power blue diode laser is developed in this work. The excitation power is enhanced by increasing the number of reflections. Comparing with a traditional photoacoustic system, the pool constant is improved from 300.24(Pa·cm)/W to 1450.64(Pa·cm)/W, and the signal sensitivity of the photoacoustic sensor is increased from 0.016 μV/ppb to 0.2562 μV/ppb. The characteristics of temperature and humidity of the new photoacoustic sensor are also obtained, and the algorithm is adjusted to provide a quantitative response and drift of the resonance frequency. The results of this research provide a new method and concept for further developing the NO2 photoacoustic sensors.

Development of a hybrid photoacoustic and optical monitoring system for the study of laser ablation processes upon the removal of encrustation from stonework

In the context of this work,a prototype hybrid photoacoustic(PA)and optical system for the on-line monitoring of laser cleaning procedures is presented.The developed apparatus has enabled the detection of MHz frequency range acoustic waves generated during the laser ablation process.The intrinsically generated PA signals combined with high resolution optical images provide the opportunity to follow the cleaning process accurately and in real time.Technical mock-ups have been used to demonstrate the potential of this novel technique with emphasis given to applications that refer to the restoration of Cultural Heritage(CH)surfaces.Towards this purpose,the real time monitoring of the laser assisted removal of unwanted encrustation from stonework has been achieved using IR and UV wavelengths.This novel approach has allowed for the precise determination of the critical number of laser pulses required for the elimination of the encrustation layer,while highlighting the dominant ablation mechanisms according to the irradiation wavelength.The promising results obtained using the prototype hybrid PA and optical system can open up new perspectives in the monitoring of laser cleaning interventions,promoting an improved restoration outcome.

Fiber laser technologies for photoacoustic microscopy

Fiber laser technology has experienced a rapid growth over the past decade owing to increased applications in precision measurement and optical testing,medical care,and industrial applications,including laser welding,cleaning,and manufacturing.A fiber laser can output laser pulses with high energy,a high repetition rate,a controllable wavelength,low noise,and good beam quality,making it applicable in photoacoustic imaging.Herein,recent developments in fiber-laser-based photoacoustic microscopy(PAM)are reviewed.Multispectral PAM can be used to image oxygen saturation or lipid-rich biological tissues by applying a Q-switched fiber laser,a stimulated Raman scattering-based laser source,or a fiber-based supercontinuum source for photoacoustic excitation.PAM can also incorporate a single-mode fiber laser cavity as a high-sensitivity ultrasound sensor by measuring the acoustically induced lasing-frequency shift.Because of their small size and high flexibility,compact head-mounted,wearable,or hand-held imaging modalities and better photoacoustic endoscopes can be enabled using fiber-laser-based PAM.

Techniques trend analysis of propagating laser beam quality measurement

Different methods of measuring a propagating laser beam quality are summarized.The disadvantages in traditional way in measuring a laser beam quality is analyzed and the insufficiencies of the Shack-Hartmannin method which is commonly using wave front technique at present is pointed out.Finally,the transmission intensity equation based(TIE-based)measuring way in a laser beam quality evaluation and the corresponding advantages are discussed,which is believed to be a deve-l oping trend in laser beam evaluation.

Improvement in resolution of fiber-laser photoacoustic tomography based on a virtual-point concept

In this study,a virtual-point concept was introduced into fiber-laser photoacoustic tomography to improve the elevational image resolution.The flexible fiber laser was bent into an arc shape to conform to the ultrasound wavefront,which formed an ultrasound focus at the center of the arc.The synthetic aperture focusing technique was utilized to reconstruct the images;as a result,the elevational resolution particularly within the out-of-focus region was considerably improved compared to the resolution of an image retrieved by multiplexing the PA time-resolved signals with sound velocity.The all-optical fiber-laser photoacoustic tomography system with a high spatial resolution has potential for various applications,including biomedical research and preclinical/clinical diagnosis.

High-speed high-resolution laser diode-based photoacoustic microscopy for in vivo microvasculature imaging

Laser diodes(LDs)have been considered as cost-effective and compact excitation sources to overcome the requirement of costly and bulky pulsed laser sources that are commonly used in photoacoustic microscopy(PAM).However,the spatial resolution and/or imaging speed of previously reported LD-based PAM systems have not been optimized simultaneously.In this paper,we developed a high-speed and high-resolution LD-based PAM system using a continuous wave LD,operating at a pulsed mode,with a repetition rate of 30 kHz,as an excitation source.A hybrid scanning mechanism that synchronizes a one-dimensional galvanometer mirror and a two-dimensional motorized stage is applied to achieve a fast imaging capability without signal averaging due to the high signal-to-noise ratio.By optimizing the optical system,a high lateral resolution of 4.8μm has been achieved.In vivo microvasculature imaging of a mouse ear has been demonstrated to show the high performance of our LD-based PAM system.

Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques

The aim of this work was to evaluate the corrosion resistance of AuPdAgIn alloy, submitted to laser beam welding, in 0.9% NaCl solution, using electrochemical techniques. Measures of the open circuit potential (OCP) versus time were applied to electrochemical experiments, as well as potentiodynamic direct scanning (PDS) and electrochemical impedance spectroscopy (EIS) on AuPdAgIn alloy, submitted to laser beam welding in 0.9% NaCl solution. Some differences observed in the microstructure can explain the results obtained for corrosion potential, Ecorr, and corrosion resistance, Rp. EIS spectra have been characterized by distorted capacitive components, presenting linear impedance at low frequencies, including a non-uniform diffusion. The area of the laser weld presented corrosion potential slightly superior when compared to the one of the base metal. The impedance results suggest the best resistant corrosion behavior for laser weld than base metal region. This welding process is a promising alternative to dental prostheses casting.

New Laser-cladding Technique for Welding of Bridge Wires in Detonators

The laser-cladding technique for welding of bridge wires is reported for the first time.The essen- tial feature of this technique different from the cur- rent methods is the realization of mutual melting of workpieces.Thus the stability of products is im- proved in an order of magnitude.The main points of the technique and the microanalyses of the weld- ing spot and other features are given.The technique presented is a novel method of welding between tiny piece and workpiece of different sizes and proper- ties.

High-speed directly modulated distributed feedback laser based on detuned loading and photon-photon resonance effect

A monolithic integrated two-section distributed feedback(TS-DFB)semiconductor laser for high-speed direct modulation is proposed and analyzed theoretically.The grating structure of the TS-DFB laser is designed by the reconstructionequivalent-chirp(REC)technique,which can reduce the manufacturing cost and difficulty,and achieve high wavelength controlling accuracy.The detuned loading effect and the photon-photon resonance(PPR)effect are utilized to enhance the modulation bandwidth of the TS-DFB laser,exceeding 37 GHz,while that of the conventional one-section DFB laser is only 16 GHz.When the bit rate of the non-return-to-zero(NRZ)signal reaches 55 Gb/s,a clear eye diagram with large opening can still be obtained.These results show that the proposed method can enhance the modulation bandwidth of DFB laser significantly.

Wind Velocity Measurement of Multi-Laser Beams Measurement System Based on Peak Delay Technique

Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high precision detection of wind field based on optical scintillations and small perturbation theory was proposed and verified. According to the fluctuation intensity of laser backscatter received by two detectors, peak delay technique was adopted to determine the velocity of wind flow. Detailed procedure to deal with backscatter signals was also presented. Then, practical experiments and measurement results showed high precision of the proposed system for wind measurement with a relative error as 3.21%. Consequently, the MLBM system possesses obvious potential application in engineering project.

Characteristics of selective oxidation during the fabrication of vertical cavity surface emitting laser

Taking into account oxidation temperature, N2 carrier gas flow, and the geometry of the mesa structures this paper investigates the characteristics of selective oxidation during the fabrication of the vertical cavity surface emitting laser （VCSEL） in detail. Results show that the selective oxidation follows a law which differs from any reported in the literature. Below 435℃ selective oxidation of Al0.98Ga0.02As follows a linear growth law for the two mesa structures employed in VCSEL. Above 435℃ approximately increasing parabolic growth is found, which is influenced by the geometry of the mesa structures. Theoretical analysis on the difference between the two structures for the initial oxidation has been performed, which demonstrates that the geometry of the mesa structures does influence on the growth rate of oxide at higher temperatures.

NONCONTACT MEASUREMENT OF ULTRASONIC VELOCITY IN LIQUID USING PULSED PHOTOACOUSTIC TECHNIQUE

Based on the theory of the pulsed photoacoustic signal in liquid generated by a pulsed laser, a novel, optically noncontact, fast and accurate method for temperature-dependent ultrasonic velocities for ethanol and water has been demonstrated. The experiment results are in good agreemerit with literature values.

Numerical investigation of multi-beam laser heterodyne measurement with ultra-precision for linear expansion coefficient of metal based on oscillating mirror modulation

This paper proposes a novel method of multi-beam laser heterodyne measurement for metal linear expansion coefficient. Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by temperature variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain the value of linear expansion coefficient of metal by the calculation. This novel method is used to simulate measurement for linear expansion coefficient of metal rod under different temperatures by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.4%.

Application of Nd:YAG Laser Welding to Implantable Neuro-Stimulator

It is difficult to weld the material and structure of implantable neuro-stimulator such as pure medical titanium and irregular outside shield by conventional arc welding methods.Currently there are few reports on the neuro stimulator sealing technology,and none of them have simultaneously considered the quality control methods.In order to develop the sealing procedure and quality control methods,an investigation of applying Nd：YAG laser welding to implantable neuro-stimulator components is carried out.Firstly,the automatic Nd：YAG laser welding system equipped with proper fixture configuration is introduced.A special fixture structure is illustrated and the key point for the device is to reduce the fit-up gap between the two shields.Then,a novel welding process technique is proposed to satisfy the engineering requirements.The optimized process parameters for titanium shell,feedthrough and fastener are provided and concluded by an orthogonal experiment.Finally,different quality control measures such as visual inspection,X-ray detecting and leakage testing,are presented on the final products.The results show that the Nd：YAG laser welding applied on the implanted neuro-stimulator under optimized parameters can prevent welding defects and improve the weld joints quality.Combination of various quality control methods will guarantee the sealing performance and mechanical properties of the products.It is confirmed that the processing procedure and quality methods can not only resolve the process technology on welding ultra-thin structure of medical device,but also provide the reference for other implantable device.