Simulation of Diode-Pumped Q-Switched Nd:YAG Laser Generating Eye-Safe Signal in IOPO Environment

Numerical simulation of diode-pumped Q-switched Nd:YAG laser leading to the generation of eye-safe signal in singly resonant Intracavity Optical Parametric Oscillator (IOPO) is presented. Starting from rate equations, the time dependent laser equations have been solved numerically, whereas the space-dependent OPO equations analytically. Our results show that 1.4 J diode laser (810 nm) pulse with 200 msec width, delivers 30 mJ Nd:YAG laser (1064 nm) pulse with 5 n-second width. This Nd:YAG laser further generates 9 mJ eye safe signal (1570 nm) pulse with 2.5 n-second width.

Femtosecond laser fabrication of 3D templates for mass production of artificial compound eyes

Compound eyes are unique optical imaging systems that consist of numerous separate light-sensitive units(ommatidia).Attempts have been made to produce artificial compound eyes via advanced 3 D nanotechnologies.Among them,femtosecond laser direct writing(FsLDW)technology has emerged as an effective strategy due to its distinct advantages in 3 D designable and high precision fabrication capability.However,the point-by-point scanning process results in a very low fabrication efficiency,limiting the practical applications of the FsLDW technology.To solve this problem,we propose a high-efficiency method for the mass production of 3 D artificial compound eyes using a photopolymer template fabricated by FsLDW.The resultant 3 D SU-8 compound eye templates could be used to replicate polydimethylsiloxane(PDMS)compound eyes many times(over 50 times)with a highly improved efficiency(nearly 20 times higher than the efficiency of direct fabrication using the point-by-point FsLDW).The PDMS replicas showed good focusing and imaging performances.We anticipate that this method may serve as an enabler for the mass production of 3 D artificial compound eyes and promote their practical applications in the near future.

Selective laser trabeculoplasty in pseudophakic and phakic eyes:a prospective study

AIM：To compare the efficacy of selective laser trabeculoplasty（SLT） in replacing medical therapy in pseudophakic and phakic eyes.METHODS：Subgroup of a prospective randomized clinical trial including patients with primary open angle glaucoma or ocular hypertension controlled with medication.Of 38 pseudophakic eyes were matched with 38 phakic eyes.SLT was offered as a way to decrease medication while maintaining the same low eye pressure.SLT was performed over 360°,at 3ns,spotsize 400 μm,100 spots.Data [intraocular pressure（IOP）,number of medications needed] were measured at 1h,1wk,1,3,6 and 12 mo.An independent-samples t-test was performed to compare baseline characteristics of the phakic and the pseudophakic group and differences in evolution of mean IOP and number of used medications.Chi-squared analysis was performed to investigate proportions of fast,slow and non-responders.RESULTS：The mean IOP measurement was 13.00± 2.88 mm Hg in the phakic group（38 eyes） and 13.51±3.06 mm Hg in the pseudophakic group（38 eyes）（P〉0.05）.This changed little after SLT and IOP lowering effect was comparable between the two groups.Main aim however was to lower the amount of medication needed.In the phakic group medication lowered from 1.29±0.62 at baseline,to 0.15±0.46 after 12mo;a reduction of 88.37%.In the pseudophakic group,used medication changed from 1.71±1.04,to 0.41±0.61;a 76.02% reduction.The differences were not statistically significant at any time point（P〉0.05）.IOP lowering occurred slightly faster in thepseudophakic group（50% of patients after one week） than in the phakic group（68% of patients after more than 4wk）.The difference was not significant（P〉0.05）.CONCLUSION：IOP lowering effect of SLT is comparable between phakic and pseudophakic eyes.

POTENTIAL SAFE TERMINATION BY LASER ABLATION OF HIGH Z IMPURITY IN THE HL-1M TOKAMAK

A preliminary experiment for triggering a plasma current quench by high Z impurities has been performed on the HL1M tokamak.Using injection of impurity with the higher charge of the nuclei allows us to increase the radiation cooling.It can be a simple and potential approach for decreasing significantly the plasma thermal energy before a disruption and for safe termination of the plasma.

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave （CW） tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode （LD） end-pumped CW 1064 nm Nd：YVO4 laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401 1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.

Corneal neuromediator profiles following laser refractive surgery

Laser refractive surgery is one of the most commonly performed procedures worldwide.In laser refractive surgery,Femtosecond Laser in Situ Keratomileusis and Refractive Lenticule Extraction have emerged as promising alternatives to microkeratome Laser in Situ Keratomileusis and Photorefractive Keratectomy.Following laser refractive surgery,the corneal nerves,epithelial and stromal cells release neuromediators,including neurotrophins,neuropeptides and neurotransmitters.Notably,nerve growth factor,substance P,calcitonin gene-related peptide and various cytokines are important mediators of neurogenic inflammation and corneal nerve regeneration.Alterations in neuromediator profiles and ocular surface parameters following laser refractive surgery are attributed to the surgical techniques and the severity of tissue insult induced.In this review,we will discuss the(1)Functions of neuromediators and their physiological and clinical significance;(2)Changes in the neuromediators following various laser refractive surgeries;(3)Correlation between neuromediators,ocular surface health and corneal nerve status;and(4)Future directions,including the use of neuromediators as potential biomarkers for ocular surface health following laser refractive surgery,and as adjuncts to aid in corneal regeneration after laser refractive surgery.

Comparison of the femtosecond Laser and mechanical microkeratome for flap cutting in LASIK

· AIM: To compare refractive results, higher-order aberrations(HOAs), contrast sensitivity and dry eye after laser in situ keratomileusis(LASIK) performed with a femtosecond laser versus a mechanical microkeratome for myopia and astigmatism.·METHODS: In this prospective, non-randomized study,120 eyes with myopia received a LASIK surgery with the Visu Max femtosecond laser for flap cutting, and 120 eyes received a conventional LASIK surgery with a mechanical microkeratome. Flap thickness, visual acuity, manifest refraction, contrast sensitivity function(CSF) curves,HOAs and dry-eye were measured at 1wk; 1, 3, 6mo after surgery.·RESULTS: At 6mo postoperatively, the mean central flap thickness in femtosecond laser procedure was113.05 ±5.89 μm(attempted thickness 110 μm), and148.36 ±21.24 μm(attempted thickness 140 μm) in mechanical microkeratome procedure. An uncorrected distance visual acuity(UDVA) of 4.9 or better was obtained in more than 98% of eyes treated by both methods, a gain in log MAR lines of corrected distance visual acuity(CDVA) occurred in more than 70% of eyes treated by both methods, and no eye lost ≥1 lines of CDVA in both groups. The difference of the mean UDVA and CDVA between two groups at any time post-surgery were not statistically significant(P 】0.05). The postoperative changes of spherical equivalent occurred markedly during the first month in both groups. The total root mean square values of HOAs and spherical aberrations in the femtosecond treated eyes were markedly less than those in the microkeratome treated eyes during 6mo visit after surgery(P 【0.01). The CSF values of the femtosecond treated eyes were also higherthan those of the microkeratome treated eyes at all space frequency(P 【0.01). The mean ocular surface disease index scores in both groups were increased at 1wk, and recovered to preoperative level at 1mo after surgery. The mean tear breakup time(TBUT) of the femtosecond treated eyes were markedly longer than those of the microkeratome treated eyes at postoperative 1, 3mo(P 【0.01).·CONCLUSION: Both the femtosecond laser and the mechanical microkeratome for LASIK flap cutting are safe and effective to correct myopia, with no statistically significant difference in the UDVA, CDVA during 6mo follow-up. Refractive results remained stable after 1mo post-operation for both groups. The femtosecond laser may have advantages over the microkeratome in the flap thickness predictability, fewer induced HOAs, better CSF,and longer TBUT.

Disruption mitigation using laser ablation of high-Z impurities in HL-1M tokamak

A preliminary experiment triggering a plasma current quench by laser ablation of high-Z impurities has been performed in the HL-1M tokamak. The injection of impurities with higher electric charges into tokamak plasmas can increase the radiation cooling of the plasma. Resistive, highly radiating plasma formed prior to the thermal quench can dissipate both the thermal and magnetic energies, which is possibly a simple and potential approach to reducing significantly the plasma thermal energy and magnetic energy before a disruption thereby a safe plasma termination is obtained.

Effect of Laser in situ Keratomileusis on Accommodation

The accommodative function before and after laser in situ keratomileusis （LASIK） was observed, and the effect of LASIK on accommodation was investigated. In a prospective clinical trial, 48 myopic patients （96 eyes） subject to bilateral LASIK in Refractive Surgery Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology （China） from March 2006 to June 2006 were selected and studied. Refractions, accommodative range, amplitude of accommodative response and high frequency component （HFC） of accommodative microfluctuations were measured with NEDIK-730A before and one week and 30 days after operation. Dominant and non-dominant eyes were determined by hole-in-card method. It was found that all of the operative eyes showed an uncorrected visual acuity of 0.8 or better one week postoperatively, and 1.0 or better 30 days postoperatively. Compared with those preoperatively, accommodative range and HFC had no significant difference at first week and 30th day after operation in both dominant eyes and non-dominant eyes （P〉0.05）, but there was a significant difference in the amplitude of accommodative response/accommodative stimulus ratio （A/S） after operation （P〈0.01）, and no significant difference was found in accommodation between one week and 30 days postoperation. No ocular dominance＇s change was noted. There was no significant difference in accommodative function between dominant eyes and non-dominant eyes. It was suggested that LASIK produced no significant effect on accommodation.

Human eye ocular component analysis for refractive state and refractive surgery

AIM： To analyze the clinical factors influencing the human vision corrections via the changing of ocular components of human eye in various applications; and to analyze refractive state via a new effective axial length.METHODS： An effective eye model was introduced by the ocular components of human eye including refractive indexes, surface radius（r1, r2, R1, R2） and thickness（t, T） of the cornea and lens, the anterior chamber depth（S1） and the vitreous length（S2）. Gaussian optics was used to calculate the change rate of refractive error per unit amount of ocular components of a human eye（the rate function M）. A new criterion of myopia was presented via an effective axial length.RESULTS： For typical corneal and lens power of 42 and 21.9 diopters, the rate function Mj（j=1 to 6） were calculated for a 1% change of r1, r2, R1, R2, t, T（in diopters） M1=＋0.485, M2=-0.063, M3=＋0.053, M4=＋0.091, M5=＋0.012, and M6=-0.021 diopters. For 1.0 mm increase of S1 and S2, the rate functions were M7=＋1.35, and M8=-2.67 diopter/mm, respectively. These rate functions were used to analyze the clinical outcomes in various applications including laser in situ keratomileusis surgery, corneal cross linking procedure, femtosecond laser surgery and scleral ablation for accommodation.CONCLUSION： Using Gaussian optics, analytic formulas are presented for the change of refractive power due to various ocular parameter changes. These formulas provide useful clinical guidance in refractive surgery and other related procedures.

Navigation technology/eye-tracking in ophthalmology:principles,applications and benefits-a narrative review

Navigation technology in ophthalmology,colloquially called“eye-tracking”,has been applied to various areas of eye care.This approach encompasses motion-based navigation technology in both ophthalmic imaging and treatment.For instance,modern imaging instruments use a real-time eye-tracking system,which helps to reduce motion artefacts and increase signal-to-noise ratio in imaging acquisition such as optical coherence tomography(OCT),microperimetry,and fluorescence and color imaging.Navigation in ophthalmic surgery has been firstly applied in laser vision corrective surgery and spread to involve navigated retinal photocoagulation,and positioning guidance of intraocular lenses(IOL)during cataract surgery.It has emerged as one of the most reliable representatives of technology as it continues to transform surgical interventions into safer,more standardized,and more predictable procedures with better outcomes.Eye-tracking is essential in refractive surgery with excimer laser ablation.Using this technology for cataract surgery in patients with high preoperative astigmatism has produced better therapeutic outcomes.Navigated retinal laser has proven to be safer and more accurate compared to the use of conventional slit lamp lasers.Eye-tracking has also been used in imaging diagnostics,where it is essential for proper alignment of captured zones of interest and accurate follow-up imaging.This technology is not routinely discussed in the ophthalmic literature even though it has been truly impactful in our clinical practice and represents a small revolution in ophthalmology.

Influence of transverse mode on retinal spot size and retinal injury effect:A theoreticalan alysis on 532-nm laser

The fundamental transverse mode(TEM00)is preferable for experimental and theoretical study on the laser-induced retinal injury effect,for it can produce the minimal retinal image andestablish the most strict laser safety standards.But actually lasers with higher order mode werefrequently used in both earlier and recent studies.Generally higher order mode leads to largerretinal spot size and so higher damage threshold,but there are few quantitative analyses on thisproblem.In this paper,a four-surface schematic eye model is established for human and macaque.The propagation of 532-nm laser in schematic eye is analyzed by the ABCD law of Gaussianoptics.It is shown that retinal spot size increases with laser transverse mode order.For relativelower mode order,the retinal spot diameter will not exceed the minimum laser-induced retinallesion(25~30μm in diameter),and so has little effect on retinal damage threshold.While forhigher order mode,the larger'retinal spot requires more energy to induce injury and so the damage threshold increases.When beam divergence is lowered,the retinal spot size decreasescorrespondingly,so the efect of mode order can be compensated.The retinal spot size of macaqueis slightly smaller than that of human and the ratio bet ween them is independent of mode order.We conclude that the laser mode order has significant influence on retinal spot size but limitedinfluence on the retinal injury ffect.

Diode Laser Cyclophotocoagulation in the Management of Pain and Intraocular Pressure Control in Patients with Terminal Glaucoma--Six Years’Experience

Objective: This study aims to describe the experience with diode laser cyclophotocoagulation in the control of intraocular pressure and resolution of pain in patients with refractory glaucoma. Methods: Retrospective study. 64 eyes of 60 patients who underwent cyclophotocoagulation between January 2008 and March 2014. Evaluation of the pre- and post-operative intraocular pressure, the control of ocular pain, the number of anti-glaucoma drugs used in pre- and post-intervention, the rate of complications and the success rate. Results: There was an overall success rate of 81.3%, with 9 eyes needing a second intervention. There was a mean reduction of 52.6% of the preoperative mean intraocular pressure of 41.25 to 19.56 mmHg at 12 months observation (p < 0.001). There was also a statistically significant reduction in the number of anti-glaucoma drugs used from 3.19 to 2.01 per eye and the resolution of pain in 75% of patients. Conclusions: cyclophotocoagulation is an effective procedure, with an expected positive impact on quality of life of patients as a result from the decreased number of anti-glaucoma drugs, sustained intraocular pressure reduction and resolution of pain.

Measuring Method of Radius of Curvature Based on Dual-Frequency Laser Interferometer

In order to achieve high-accuracy measurement of radius of curvature of optical sphere, ultra-high accuracy radius of curvature testing device is developed by dual-frequency laser interferometer and Fizeau interferometer based on cat’s eye and confocal method. Through analyzing the error source models of radius of curvature testing, optical configuration of the testing device has been optimized. Precise environment control and real-time monitoring system is also established to reduce the errors caused by environment. Through the above processes, the radius of curvature measurement relative accuracy is better than 2 ppm. One optical sphere, R88.5 mm, test aperture 59 mm, has been tested. Testing result is 88499.465 ± 0.176 μm, meeting the design requirement. The method has high accuracy and practical advantages.

脉冲激光测距光源进展

简要介绍用于激光测距的各种光源 :Nd∶YAG激光器、CO2 激光器、Er∶glass激光器、喇曼频移Nd∶YAG激光器、OPO激光器和半导体激光器 ,并对它们的研究进展和应用前景进行了阐述。

人眼安全1.57μm OPO激光测距机

研制成功人眼安全 1.57μmOPO激光测距机 ,并进行了室外测距实验 ,在能见度V约10km时测到 70 50m远处的烟囱 ,测距精度± 5m ,重复频率达 2 0 pps。该测距机采用紧凑小型的水冷灯泵电光调Q (Ce ,Nd)∶YAG激光器泵浦磷酸钛氧钾 (KTP) 1.57μm单谐振OPO器件 ,输出12mJ ,脉宽～ 6ns。接收元件选用铟镓砷 (InGaAs)PIN探测器。

1.57μm内腔光学参量振荡器研究

对内腔光学参量振荡器的工作机理进行了简要分析 ,报道了一种高效、紧凑的 1.5 7μm人眼安全内腔光学参量振荡器的实验结果。它的泵浦源为水冷闪光灯泵浦KD P电光调Q (Ce ,Nd) :YAG激光器 ,采用KTPⅡ类非临界相位匹配 ,输出信号光脉冲能量最高达 87.7mJ ,脉宽约7ns ,重复频率为 10Hz ,总电光效率最高达 5 .8‰ ,器件外形尺寸为 4 10mm× 130mm× 80mm。

高速公路车辆防追尾碰撞系统的设计与控制研究

针对汽车追尾碰撞事故频发和事故中驾乘人员头颈部易受损伤等问题,利用激光雷达测距和机电控制相结合的技术,提出了一种车辆防追尾碰撞系统,对高位制动灯和主动式头枕进行控制。首先利用激光雷达和本车状态信息对行车环境进行预测;接着对后车分液压和气压两种制动形式进行行车安全车距的分析,推导出临界安全车距的计算公式;最后通过AT89C51单片机系统预设的程序,将实际行车间距与临界安全车距进行比较,并据此控制高位制动灯的开闭和主动式头枕控制系统的执行。所提出的方法有较好的工程实用性。

Nd:GYSGG/YVO_4双波长人眼安全波段内腔拉曼激光器

以Nd:GYSGG晶体为激光增益介质,a切割YVO4晶体为拉曼增益介质,利用Nd:GYSGG晶体的双波长激光运转特性实现声光调Q 1.5μm人眼安全波段双波长内腔拉曼激光器。为克服Nd:GYSGG晶体严重的热透镜效应对激光器功率的限制,实验确定其同带泵浦吸收峰位置及吸收系数,采用同带泵浦方式减轻热效应。吸收882.9 nm泵浦光功率17.1 W时,在20 k Hz的脉冲重复频率下获得1.44 W的1.5μm双波长输出,转换效率8.4%,光束质量因子M2=2.4;棱镜分光测得其中1 497 nm和1 516 nm功率分别为0.55 W和0.89 W,二者脉冲宽度相近,均为15.3 ns左右。与808 nm传统泵浦相比,同带泵浦方式下激光器的输出功率及光束质量均得到明显提升。

人眼安全的生物气溶胶短程遥测系统

建立了满足激光辐照人眼安全要求的便携式生物气溶胶短程遥测系统,用于实现有人员活动区域生物战剂气溶胶的实时预警监测。以高频调制的405nm半导体激光器为激发光源,200mm口径的卡塞格林望远系统为信号光收集系统,搭建了基于伪随机调制的便携型生物气溶胶激光雷达短程遥测系统。该系统具备平行偏振散射、垂直偏振散射光探测,以及450nm和530nm两个波段荧光探测等四个同步探测通道。以枯草芽孢杆菌、金黄色葡萄球菌和酵母菌为样本对该激光雷达系统进行了初步测试。外场试验表明,该生物气溶胶遥测系统的空间分辨率为1.5m,荧光通道的探测距离为100m;3种被测生物气溶胶种类识别的回代误报率分别为9%、11.5%和14.5%,交叉误报率为11.3%。该遥测系统的激光能量低于激光辐照人眼安全标准的要求,基本实现了生物气溶胶的甄别。