Theoretical model of CO2 laser ablation of soft-tissue phantoms

Summary A model of thermal laser ablation of soft tissues is developed taking into consideration two mechanisms: evaporation and liquid moving, due to vapour pressure gradient. Usually a soft tissue is modelled as a single-component material with thermal and optical properties very similar to those of water. We examined the non-stable kinetics of the evaporation process, for short-pulse infrared laser ablation of soft tissues, and we also calculated the average liquid velocity and the ablation rates under vapour pressure gradient. The theoretical results are in good agreement with previous reported experimental data on gelatin and polyacrylamide tissue phantoms The authors of this paper have agreed to not receive the proofs for correction     

A raman spectroscopic study of the interactions of 13 GHz microwave irradiation with dipalmitoylphosphatidylcholine dispersions

Summary In order to clarify the effect of 13 GHz microwave irradiation upon model membranes, vibrational Raman spectroscopy was performed for multilamellar dispersions of dipalmitoylphosphatidylcholine, before and after irradiation. Raman spectra of the phospholipid dispersions were recorded for the C−H ((2800⊢3100)cm⁻¹) and the C−C ((1050⊢1150)cm⁻¹) stretching modes, above the transition temperatureT _m of the phospholipid, before and after microwave irradiation. An intensity comparison between the irradiated and nonirradiated sample revealed an increase in the intensity ratioI ₂₉₃₀/I ₂₈₈₀ and a small perturbation in the C−C stretching region, induced by microwaves. It seems reasonable to assume that microwave irradiation brings about a change in lateral chain-chain interactions, which is possibly due to induced changes at bilayer curvature.     

Laser Keratectomy for correction of presbyopia

Summary We suggest that even an elementary analysis of a traditional model (Gullstrand) for the human eye is suitable for programming correction of the presbyopia by laser keratectomy: indeed, the application of our simple calculations was successful in simulations as well as in subsequent operations in hospital.     

Multiple beam scattering effects in biological tissues exposed to laser radiation

Summary A mathematical model is presented for the computation of intensity of radiation in biological tissues irradiated by laser. The time-independent transport radiative equation is solved in terms of a Neumann series. Each term of the series is associated with a different order of magnitude of the internal-scattering effect. The importance of these effects has been recognized during the irradiation by ion-argon and ND: YAG laser used as coagulting or cutting instruments in surgery applications. Agreement is found with the single-scattering picture.

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Riassunto Si presenta un modello matematico per calcolo dell'intensità della radiazione nei tessuti biologici esposti a radiazione laser. L'equazione del trasporto radiativo indipendente dal tempo è risolta con la serie di Neumann. Ogni termine della serie rappresenta ordini di grandezza differenti dell'effetto di scattering interno. Questi effetti divengono importanti durante l'irraggiamento con laser ad argon e ND: YAG utilizzati in applicazioni mediche per la coagulazione e l'incisione. Il modello è in accordo al primo ordine con il termine di scattering singolo.

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Резюме Предлагается математическая модель для вычисления интенсивности излучения в биологических тканях, подверженньх лазерному облучению. С помощью рядов Неймана решается не зависящее от времени уравнение переноса излучения. Каждый член ряда связан с различным порядком величнины эффекта внутреннего рассеяния. Определяется важность эффектов многократного рассеяния при облучении ион-аргоновым лазером и ND: YAG лазером, которые ирользуются как инструменты коагуляции или резания в хирургии. Показывается, что процесс взаимодействия соответствует картине однократного рассеяния.

     

Biostimulation of HeLa cells by low-intensity visible light. V. Stimulation of cell proliferationin vitro by He−Ne Laser irradiation

Summary Autoradiographic experiments, performed with monolayer HeLa cells, show that the irradiation with He-Ne laser (D=100 J/m²) causes an increase in the number of S-phase cells connected with enhanced G₁-S transition of a part of the population, as well as an increase in the grain count on the labelled nuclei connected with an enhancement of DNA synthesis in Sphase cells. The irradiation influences the proliferation rate of various subpopulations not in equal degree, as shown analysing the clone size distribution after the irradiation (D=10, 10², 10³J/m²). The stimulative effect of irradiation is most noticeable on the proliferation activity of the slowly growing subpopulations.

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Riassunto Esperimenti autoradiografici, attuati su un monostrato di cellule HeLa, mostrano che l’irraggiamento con un laser He-Ne (D=100J/m²) causa l’aumento del numero delle cellule in fase S connesso con un aumento della transizione G₁-S di una parte della popolazione, nonché l’aumento dei granuli nei nuclei marcati, connesso con un aumento della sintesi del DNA nelle cellule in fase S. L’irraggiamento influenza la velocità di proliferazione di varie sottopopolazioni non in misura uguale a quella mostrata analizzando la distribuzione delle dimensioni del clone dopo l’irraggiamento (D=10, 10², 10³J/m²). L’effetto stimolatorio dell’irraggiamento si nota di piú sull’attività proliferativa delle sottopopolazioni in crescita lenta.

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Резюме Авторадиографические эксперименты, проведенные с монослоем клеток HeLa показали, что облучение He-Ne лазером (D=100 ДжМ²) приводит к увеличению количества клеток вS-фазе, связанному с ускорением перехода части популяции изG ₁ вS-фазу. Также отмечено увеличение количства зерен в меченых ядрах, связанное с ускорением синтеза ДНК в клеткахS-фазы. Облучение влияет на скорость пролиферации различных субппопуляций в разиой степени как показал анализ распределения размеров клонов после облученияD=10, 10², 10³ Дж/М². Эффект стимуляции пролиерации наиболее заметен в случае медленно растуших субпопуляций.

     

Fluorine absorption in dental enamel assisted by UV irradiation

Summary A new method of dental fluorine prophylaxis based on the chemical reaction induced by UV irradiation in dental enamel has been presented. Fluorine ions from a gel topic can be retained to the dental apatite in the lamp-irradiated samples at about 70% and in the laser-irradiated samples at about 80% of the maximum deposited value. The¹⁹F(p,α)¹⁶O nuclear reaction was used to measure the fluorine concentrations in the first 3 μm of the enamel of healthy teeth before and after the gel topic applications with and without UV irradiation. This method of dental prefenction resolves the problem of the traditional fluorine prophylaxis which brings fluorine in the enamel without binding the apatite. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

大功率TEA CO2激光器系统中电磁干扰的抑制

大功率TEA CO2激光器系统产生的强电磁干扰主要来源于激光器主放电回路、脉冲火花开关和电源。这种强电磁干扰使大功率TEA CO2激光器控制子系统出现数据混乱、显示屏帧频滚动及功率模块损坏等电磁兼容问题。对大功率TEA CO2激光器系统中产生强电磁干扰的部位和干扰途径进行了测试及分析。通过调整放电回路的参数降低电磁干扰强度,采用埋入式同轴高压电连接器专利技术对主放电回路进行屏蔽,控制子系统选用PLC为控制核心及屏蔽滤波,软件中输入及输出程序的抗干扰设计等措施,有效地抑制了干扰电磁波在系统内外的传播,解决了大功率TEA CO2激光器系统电磁兼容问题。结果表明:主动降低电磁干扰强度和对电磁干扰源进行屏蔽,提高控制子系统硬件抑噪能力等措施,是抑制电磁干扰,保证激光器控制子系统硬件不受损坏的主要手段。软件抗干扰,是硬件抑制电磁干扰措施的补充和延伸,能使激光器系统具有很高的可靠性。     

具有同空间特性的双波长可调谐TEACO2激光器

研制成功一种新型双波长TEACO2激光器,激光器在一对横向放电电极之间设置两个空间部分重叠的光栅_平面腔,两光栅沿腔轴一前一后放置,且在空间上交叠,两个腔相互利用,能够输出含有两种波长成分的激光脉冲。输出的同一激光脉冲中两波长激光场在空间上部分重叠,重叠程度和两种波长激光场的能量比均可通过调整前面光栅的水平横向位置加以控制,通过调节两光栅的角度选择所需支线,波长调谐方便且调谐范围较宽。该激光器在分离硼同位素的实验中得到了初步成功的应用。     

管状预电离可调谐TEA CO2激光器.

研制了一种新型的预电离结构--管状预电离器,并将其应用于可调谐TEA CO2激光器.利用光栅选线方案,采用光栅谐振腔,实现了激光的调谐输出.在输出耦合率为50%、气压为40 kPa的条件下,10P(20),10R(20),9P(20),9R(20)四条谱线获得的最高电光转换效率,分别为9.5%,9.7%,9.8%,9....     

高功率TEA CO2激光器两波长激光切换输出技术

 以TEA CO₂激光器通常采用的平-凹光学稳定腔为基础,提出了一种新的波长选支方法——输出窗口镀膜选支方法。利用一台高平均功率TEA CO₂激光器进行了选支实验研究,结合现有光学镀膜技术,得到了中心波长为9.3 μm的激光单谱线输出,其单脉冲能量及平均功率与激光器原中心波长10.6 μm单谱线输出的相应参数基本相当。研究发现,以相同单脉冲能量激光照射热敏纸时,中心波长9.3 μm激光光斑与中心波长10.6 μm的明显不同。同时,还设计出两波长窗口密闭免调切换装置,在一台激光器上实现了10.6,9.3 μm两个中心波长激光同等功率水平的免调切换输出,切换位置误差小于5″,密封性能满足使用要求。     

Time-resolved spatial structure of TEA CO2 laser pulses

The evolution of the intensity profile of TEA CO₂ laser pulses along the pulse length is investigated both analytically and experimentally. A simple scalar model of the pulse amplitude is introduced, which gives the loaded-cavity modes as a linear combination of bidimensional Hermite-Gauss functions. According to this model a number of equations are derived which link the time-varying spatial structure of the pulse to its time-resolved second-order intensity moments, namely, the beam width and the M² parameter.     

一种新型TEA CO2激光器的实验研究

设计了一种新型结构的激光器———双通道放电激励折叠腔TEA CO2激光器。该激光器通过提高脉冲能量输出水平来增加激光输出谱线数目和激光差分吸收雷达可探测的气体种类。它在增大激光器放电时间长度的同时保证了较小的激光器体积,更好地满足了激光差分吸收雷达光源体积小,重量轻,输出能量高的要求。得到激光器输出能量与气体工作气压的关系曲线,获得了激光器内工作气压与输出脉宽关系曲线,发现脉冲宽度大约在50~70ns之间变化,研究了气体压强对激光器输出脉冲峰值功率的影响。     

紫外预电离TEA CO2激光器放电特性的实验研究

横向激励大气压（transversely excited atmospheric,TEA）CO2激光器的放电稳定性是决定该类型激光器应用效果的关键因素。通过对采用电感充放电电路的紫外预电离激光器的实验研究,得到了激光器放电动态过程的规律,并发现残余振荡是主放电后发生弧光放电的主要原因。实验中采用不同配比的气体,并对电感充放电电路与改进后的硅堆充放电电路进行了比较。实验结果表明：增加充电电感值可以降低主放电结束后储能电容上的残余电压;而采用硅堆放电电路在主放电后仅有相对幅值很低的稳定残压,两种方案都大幅度抑制了弧光放电的形成,有效地提高了激光单脉冲能量。     

TEA CO2激光器非对称电极系统的电场分布

 设计了一种非对称电极,这种非对称电极的阳极是Chang电极或Ernst电极,阴极是由直线和圆弧构成的简单电极。通过比较和分析非对称电极和对称电极的特点发现,非对称电极系统中简单电极的边缘电场起伏最大。采用有限元方法计算了非对称电极系统中的简单电极取不同的直线长度和弧线半径时,非对称电极系统的电场分布,给出了选择非对称电极系统中的简单电极参数的依据。结果表明：这种非对称电极系统结合了解析电极和简单电极的优点,通过选择非对称电极系统的简单电极参数,它可以在TEA CO₂激光器中产生边缘电场起伏小于0.06,且满足电极表面均匀场面积宽度要求的电场。     

TEA CO2激光器几种放电电极的比较

 从均匀场电极理论出发，计算并讨论了近似Rogowski电极、Chang电极(含紧凑式Chang电极)和Ernst电极的形状、理论电场分布和实际电场分布。对实验室所用的几种电极进行了脉冲放电实验，从而获得了TEA CO₂激光器的放电参数与输出特性，并对这些结果进行了比较和分析。计算表明，在基本参数相同的情况下，Ernst电极具有最紧凑的外形和最佳的均匀电场分布。实验表明，采用近似Rogowski电极的TEA CO₂激光器具有最大放电辉光范围和44 kV的最小放电击穿电压；采用Ernst电极的TEA CO₂激光器具有25 J的最高单脉冲能量和最大17.2%的斜率效率。最后提出了TEA CO₂激光器主电极的选择建议。     

TEA CO2激光器几种放电电极的比较

从均匀场电极理论出发,计算并讨论了近似Rogowski电极、Chang电极(含紧凑式Chang电极)和Ernst电极的形状、理论电场分布和实际电场分布。对实验室所用的几种电极进行了脉冲放电实验,从而获得了TEA CO2激光器的放电参数与输出特性,并对这些结果进行了比较和分析。计算表明,在基本参数相同的情况下,Ernst电极具有最紧凑的外形和最佳的均匀电场分布。实验表明,采用近似Rogowski电极的TEA CO2激光器具有最大放电辉光范围和44 kV的最小放电击穿电压;采用Ernst电极的TEA CO2激光器具有25 J的最高单脉冲能量和最大17.2%的斜率效率。最后提出了TEA CO2激光器主电极的选择建议。     

TEA CO2激光器序列带的输出特性

采用双光栅谐振腔和增长放电增益区,进行了TEA CO2激光器弱线输出特性研究。在CO2,N2,He气体体积比为0.16∶0.21∶0.63,总压强为57.3 kPa情况下,获得6条11 μm波长附近弱线(序列带和热带)激光输出,谱线脉宽为400 ns左右。研究了011-030带的P19线的输出波形和能量,结果表明：谱线输出能量随光栅中心的位移变化而变化,当光栅中心在放电区中心轴线上时输出最强,最大输出能量达几百mJ。     

大功率TEACO2非稳腔激光器的远场传输特性

针对大功率激光器的远场传输特性,提出了一种测量TEACO,远场光束传输特性的新方法,该法采用相对测量和绝对测量相结合的方式来获得高能激光器的绝对空间光强分布。利用该方法测试了2kW脉冲TEACO,非稳腔激光器在500m处的光强分布,并对测试结果进行了分析讨论。实验结果表明,此方法简单、易行,准确度较高,而且测量过程中考虑了大气湍流的影响,光斑强度相对分布上出现了平顶、破碎并出现旁瓣现象,实测大气透过率为81．5％,最大功率密度为1．59W／cm^2,光束的横向远场发散角达到0．64mrad,基本与理论计算结果相吻合。本研究将为评估激光系统的应用效果及系统的优化设计提供重要的参考。     

紫外预电离TEA CO2激光器放电特性的实验研究

 横向激励大气压（transversely excited atmospheric,TEA）CO₂激光器的放电稳定性是决定该类型激光器应用效果的关键因素。通过对采用电感充放电电路的紫外预电离激光器的实验研究，得到了激光器放电动态过程的规律，并发现残余振荡是主放电后发生弧光放电的主要原因。实验中采用不同配比的气体，并对电感充放电电路与改进后的硅堆充放电电路进行了比较。实验结果表明：增加充电电感值可以降低主放电结束后储能电容上的残余电压；而采用硅堆放电电路在主放电后仅有相对幅值很低的稳定残压，两种方案都大幅度抑制了弧光放电的形成，有效地提高了激光单脉冲能量。