Cr^4＋：YAG的可饱和吸收特性与被动Q开关性能研究

运用速率方程计算了Ｃｒ＾４＋：ＹＡＧ晶体的可饱和吸收特性参数，包括初始吸收系数，饱和吸收系数，饱和光强和损耗调制度，用Ｃｒ＾４＋：ＹＡＧ对脉冲和连续Ｎｄ：ＹＡＧ激光器进行了被动调Ｑ，在脉冲Ｎｄ：ＹＡＧ激光器上得到了８ｎｓ的调Ｑ激光脉冲，在连续Ｎｄ：ＹＡＧ激光器的调Ｑ中得到了间隔和幅度抖动小于５％的输出脉冲充列。     

LD泵浦Nd:YAG微片激光器

ＬＤ泵浦Ｎｄ：ＹＡＧ微片激光器结构简单紧凑，与半导体激光器相比，前者具有激光线宽窄、光束质量好、相干长度长等优点，因此在一些测量领域有着较好的应用前景。目前对ＬＤ泵浦Ｎｄ：ＹＡＧ微片激光器的实验工作主要是获得单频、单模连续输出和线性频率调制特性研究。本文综述了近几年来ＬＤ泵浦Ｎｄ：ＹＡＧ微片激光器的研究方向、成果及应用，主要介绍了各国对ＬＤ泵浦Ｎｄ：ＹＡＧ微片激光器的调频特性的研究状况     

Cr^4＋：YAG在对撞脉冲锁模的Nd：YAG激光器中实现被动锁模的研究

在理论上提出了Ｃｒ＾４＋：ＹＡＧ作为可饱和吸收体在Ｎｄ：ＹＡＧ激光器中实现被动锁模的可能性，运用速率方程组导出在强激光脉冲作用下Ｃｒ＾４＋：ＹＡＧ激发态吸收的恢复时间和饱和光强。实验上在带有抗共振环结构的接近于介稳腔的脉冲式Ｎｄ：ＹＡＧ激光器中用Ｃｒ＾４＋：ＹＡＧ作为可饱和吸收体实现被动锁模运转，得到能量１３．５ｍＪ、平均脉宽１８０ｐｓ的锁模脉冲序列。     

二极管泵浦的高效连续波基横模Nd：YAG激光器

报道了用激光二极管端面泵浦的高效连续波ＴＥＭ００模Ｎｄ：ＹＡＧ激光器，最大输出为０．６５Ｗ，斜效率５１％，光－光效率最高达４０．６％，并给出了耦合光学系统和二极管泵浦Ｎｄ：ＹＡＧ激光器的器件结构．     

二极管泵浦的高效连续波基横模Nd：YAG激光顺

报道了用激光二极管端面泵浦的高效连续波ＴＥＭ００模Ｎｄ：ＹＡＧ激光器，最大输出为０．６５Ｗ，斜效率５１％，光－光效率最高达４０．６％，并给出了耦合力学系统和二极管泵浦Ｎｄ：ＹＡＧ激光器的器件结构。     

连续Nd:YAG激光高重复率电光调Q研究

研究了连续Ｎｄ：ＹＡＧ激光器中由于热效应使ＹＡＧ棒产生的双折射引起传输的线偏振光退偏为椭圆偏振光的退偏现象所产生的输出不稳定和多模的原因。电光调Ｑ技术被应用于连续氪灯抽运的Ｎｄ：ＹＡＧ激光器件。为了获得稳定、单模的输出,在谐振腔内放置了一对λ／４波片。通过实验研究,实现了重复频率１～６ｋＨｚ的窄脉冲激光输出,这将为连续抽运的Ｎｄ：ＹＡＧ激光器提供一种新的电光调Ｑ技术。     

LD泵浦Nd：YAG激光器的强度噪声特性研究

本文在理论研究了ＬＤ泵浦Ｎｄ：ＹＡＧ激光器的强度噪声特性，用传递函数的形式给出各种噪声湿源对激光器强度噪声的影响，计算结果指出，Ｎｄ：ＹＡＧ激光器输出的激光并非相干态光场，在几兆频率上存在高于散粒噪声基准几十ｄＢ的驰豫振荡噪声，在小于驰豫振荡频率范围，激光器的强度噪声基本上处于泵浦泵噪声水平。     

横向抽运产生高效率的可调谐Ce：LICAF激光器

横向抽运产生高效率的可调谐Ｃｅ：ＬＩＣＡＦ激光器一种增益开关Ｃｅ３＋：ＬＩＣＡＦ激光器在２８８ｎｍ产生了高达１０ｍＪ的输出。Ｎａｖａｌ研究实验室的科学家们横向抽运了Ｌｉｓｎｔｎｉｎｇ光学公司的一块８Ｘ８Ｘ３０ｍｍ布儒斯涅切割晶体，由千信频Ｎｄ：ＹＡＧ...     

激光二极管端面泵浦的调Q内腔倍频Nd：YAG激光器

报道了用两个１．５Ｗ激光二极管偏振耦合端面泵浦的声光调Ｑ内腔倍频Ｎｄ：ＹＡＧ激光器。输出５３２ｎｍ绿光重复频率１ＫＨｚ时，最大峰值功率为２．２３ＫＷ，最窄脉宽为１８ｎｓ，平均功率４０ｍＷ。最高重复频率３０ＫＨｚ。重复频率１５ｋＨＺ时，最高平均率１２８ｍＷ。对声光调Ｑ内倍频Ｎｄ：ＹＡＧ激光器的动态特性进行了理论分析及计算。     

内泵浦的小型管状Nd：YAG激光器的初步实验研究

介绍了小型化的内泵浦管状Ｎｄ：ＹＡＧ激光器的设计及初步实验结果，斜效率达２．７３％，得到了近３Ｊ的脉冲能量输出。     

Effect of film properties on the material removing characteristics in femtosecond laser rear-side ablation of chromium film

The microfabrication of films with femtosecond lasers has been researched widely for its high spatial resolution and sub-spot-size features. Compared with the common front-side ablation, femtosecond laser rear-side ablation mechanism of films is more complex due to the possible film breaking process. In this paper, the effect of film properties such as adhesion strength and cohesion strength on the material removing characteristics in femtosecond laser rear-side ablation of Cr film is investigated. The possible film breaking process in the rear-side ablation is analyzed firstly, and then some experiments with different films, the vapor deposited Cr film, the sputtered Cr film and the Cr film of photomask are performed. The experimental results indicate that the film properties are key factors influencing material removal characteristics for laser rear-side ablation. By varying film properties and laser fluence, femtosecond laser rear-side ablation technique can be applied in laser cleaning process and fabrication of nanostructures. The unique feature of rear-side ablation will widen the application of femtosecond laser micromachining technique.     

Ultrafast double pulses ablation of Cr film on glass

Ultrafast lasers ablation of Cr film was investigated by using double-pulse method. Experimental results show that there exists a temporal ablation window effect with each of the double pulses adjusted just smaller than the threshold. When the delay between the double pulses is within the order of 400 ps, the ablation of Cr film could happen. When the delay between the double pulses is beyond the order of 400 ps, the ablation of Cr film would not happen, and the reflectivity from the surface of the Cr film shows a sharp rise at the same time. The two-temperature model was developed into the form of double pulses to explain the experimental phenomena. Furthermore, microbump structures were formed on the surface of Cr film after ablation by ultrafast double pulses. Their heights exhibit an obvious drop between 1 and 10 ps double pulses delay, which is involved with the electron-phonon coupling process according to the numerical simulation. These results should be helpful for understanding the dynamic processes during ultrafast lasers ablation of metal films.     

Damage mechanism and morphology characteristics of chromium film in femtosecond laser rear-side ablation

In this paper, damage mechanism and morphology characteristics of chromium film in femtosecond laser rear-side ablation are investigated. The film removing process includes two key sub-processes: the laser ablation dynamic process and subsequent breaking and ejecting dynamic process. Film morphology in rear-side ablation is determined by the interrelation between the laser energy and the film strength. When lower laser energy is used, residual out-layer film is relative thick and tends to break into some large fragments, which results in an irregular ablation shape. While when higher pulse energy is used, thinner residual film with weaker break strength breaks into small fragments, the ablation quality improves correspondingly. Besides laser energy and film property, energy distribution of laser beam also affects the ablation quality. In experiments, this kind of effect is researched by changing the focal position. It is found that ripples, which are familiar nano-structures in front-side ablation, also exist in rear-side ablation. These ripples are formed initially at the interface between quartz substrate and film, and their coverage varies with the energy distribution. Additionally, increasing number of scans is an effective method to shorten the period of ripples.     

355 nm nanosecond pulsed Nd:YAG laser profile measurement, metal thin film ablation and thermal simulation

Laser ablation of nickel, gold and copper thin film on glass substrates has been investigated using a nanosecond pulsed Nd:YAG laser operating at 355 nm in air with a Gaussian intensity profile. The exact beam profile was measured through mechanical scanning with a photodiode. A small beam defect was observed, which can affect the machining performance at higher pulse energies. The ablation thresholds of the films were calculated from the crater diameter values. The effect of the pulse repetition rate and the film thickness was also studied. At high pulse repetition rates heat accumulation was observed and the ablation threshold decreased with the film thickness. Both cases resulted in higher diameters.     

Effective removal of adhering cells via ultrashort laser pulses

A technique for accurately and effectively removing adhering red blood cells in a blood plasma thin film via a picosecond pulsed laser was developed. The laser beam was focused to the surface of the film to generate plasma-mediated ablation and an automated stage was employed for raster scan. The SEM images showed that the red blood cells distributed in the ablation scanned area were removed neatly, leaving the surroundings and the film base intact. For cells across the boundary between the ablated and untreated areas, a trim cutting interface was observed. Complete ablation of red blood cells in the target area is achieved without visible thermal and collateral damage in the remaining structure. The removal method is very effective because it is not necessary to selectively focus a laser beam on individual target cells and remove cells one by one. The ablation is scanned over a certain size of area, enabling practical cell killing or microbial decontamination in clinical/industrial scale.     

Evaluation of excimer laser ablation of thin Cr film on glass substrate by analysing acoustic emission

Excimer laser ablation of a thin Cr film on a glass substrate was evaluated through detecting acoustic emission arising from the ablation process and observing surface morphology. In the experiment, an acoustic emission transducer was coupled to the sample to acquire acoustic emissions of laser–material interaction and an oscilloscope was used to record the signals. The patterned areas were examined by using an optical microscope. Characteristics of the acoustic emissions were studied through applying a range of signal analysis tools. Several features (e.g., average power, RMS) showed a clear linkage with the ablation mechanism of thin Cr film when varying the fluence of the laser source. Moreover, the damage to the glass substrate was well discriminated by the extracted features. In sum, evaluation of acoustic emissions not only provided a tool to study the ablation mechanisms of the thin metal film but also addressed a monitoring strategy for excimer laser micromachining.     

Ultrafast laser ablation of indium tin oxide thin films for organic light-emitting diode application

Ultrafast laser ablation of ITO thin film coated on the glass has been investigated as a function of laser fluence as well as the number of laser pulses. The ablation threshold of ITO thin film was found to be 0.07 J/cm² that is much lower than that of glass substrate (about 1.2–1.6 J/cm²), which leads to a selective ablation of ITO film without damage on glass substrate. The changes in the electrical resistance and morphology of ablated trench of ITO electrode were found to be strongly dependent on the processing conditions. We present the performance of organic light-emitting diodes (OLED) fabricated with ITO electrode patterned by ultrafast laser ablation.     

The influence of thermal diffusion on laser ablation of metal films

Single-shot ablation thresholds of nickel and gold films in the thickness range from 50 nm to 7 m have been measured for 14 ns laser pulses at 248 nm, using photoacoustic shock wave detection in air. The metal films were deposited on fused silica substrates. The ablation threshold was found to increase linearly with film thickness up to the thermal diffusion length of the film. Beyond this point it remains independent of film thickness. The proportionality between threshold fluence and thickness allows the prediction of ablation thresholds of metal films from the knowledge of their optical properties, evaporation enthalpies and thermal diffusivities. Physically it proves that ablation is driven by the energy density determined by the thermal diffusion length. A simple thermodynamic model describes the data well. Thermal diffusivities, an essential input for this model, were measured using the technique of transient thermal gratings. In addition, the substrate dependence of the ablation threshold was investigated for 150 nm Ni films.     

Numerical simulation of the ablation of thin molybdenum films under laser irradiation

Laser irradiation of a molybdenum film on a quartz substrate is numerically studied. The simulated results prove the experimental effect lying in a threefold decrease in the size of the ablation region in comparison with the focal spot. The numerical experiment proves the hypothesis on the two-stage ablation of metal film with the primary formation of oxide phase. It is demonstrated that oxidation leads to a selective decrease in the thermal resistance of the film along the vertical direction, so that the anisotropic character of the ablation is enhanced.     

Shadowgraphy investigation of laser-induced forward transfer: Front side and back side ablation of the triazene polymer sacrificial layer

Thin films of a photodecomposible triazene polymer are used as sacrificial layer for the micro-deposition of sensitive materials by laser-induced forward transfer. To understand the ablation process of this sacrificial layer, the ultraviolet laser ablation of triazene films was investigated by time-resolved shadowgraphy. Irradiation from the film side shows a complete decomposition into gaseous fragments, while ablation through the substrate causes ejection of a solid flyer of polymer. The occurence of the flyer depends on the film thickness as well as on the applied fluence, and a compact flyer is obtaind when these two parameters are optimized.