This paper reported a high-power diode-pumped solid-state laser for material processing applications with a target of more than 60 ns pulse width at 355 nm. As known, long pulse width IR laser (around 70-100 ns) is difficult to get high conversion efficiency to UV since the peak power is more than 2 times lower than 20-30 ns laser. However, the unique long pulse width characteristic makes the laser an ideal tool for flexible PCB drilling with 30-50 μm holes and for cutting portable devices. Up to 52.2% IR to UV conversion efficiency was obtained by our novel intra-cavity harmonic generation cavity design. A 9.3W UV output at 30 kHz was demonstrated with compact intra-cavity sum frequency design. Special conduction cooling-designed LD side-pumped module provided 17.8 W fundamental IR output power with AOM q-switching. The UV output pulse width is 76 ns at 30 kHz and 140 ns at 70 kHz. The type I and type II phase matching LBOs were used for intra-cavity harmonic generations of 355 nm. The output characteristics of the IR and the harmonic generations varying with the pulse repetition rate were also investigated. The experimental results are in agreement with the theoretical modelling. This system will also be useful for many material processing applications such as PCB cutting and wafer scribing.
In high power diode pumped solid-state lasers, thermal effects in the laser medium are important factors limiting the power scaling and beam quality. Besides total pump power, pump structure, such as pump geometry, cooling scheme, laser crystal shape and dimension all affect the result of thermal effects. The theoretical modelling and calculations may only conclude approximate results with the consideration of parts of factors. This paper introduces a new technique of measuring Nd:YAG rod thermal lensing by digital holography (DH). Both dynamic and steady state can be measured by this method. The digitally recorded hologram can reveal each part of the thermal effects in the crystal, and detailed variations of thermal effects can be mapped out through digital reconstructions of the captured holograms. It can help to study the uniformity of the pump distribution in the gain medium, find "hot" spots which may result in potential crystal crack. Moreover, an integrated thermal lensing can be accurately determined. DH is an informative tool to understand thermal effects and provide a guidance for laser cavity design and simulations.
This paper reports a high power diode pump 5th harmonic generation of Nd: YAG laser system, which could generate up to 300 mW TEM00 mode output with 100 Hz repetition rate at 213 nm. A diode pump module was specially designed for a high efficiency and good beam quality at the fundamental wavelength 1064 nm. An amplifier was set up out of the cavity to boost up the energy level of fundamental wavelength. In order to get high efficiency of the 5th harmonic generation, the cavity of the fundamental wavelength is EOM Q-switched which could generate very high peak power of the fundamental wavelength laser for extra cavity harmonic generations. Finally, 14% conversion efficiency from IR to UV was achieved, which is the highest efficiency in the market to the best of our knowledge right now. 213 nm is a very good substitute wavelength of 193 nm for different UV applications, the system of which is more compact, higher energy, less maintenance and better beam quality than the system of 193 nm.
In this paper we presented a pulse shaping technique on regular solid-state lasers and the application in semiconductor
micromachining. With a conventional Q-switched laser, all of the parameters can be adjusted over only limited ranges,
especially the pulse width and pulse shape. However, some laser link processes using traditional laser pulses with pulse
widths of a few nanoseconds to a few tens of nanoseconds tend to over-crater in thicker overlying passivation layers and
thereby cause IC reliability problems. Use of a laser pulse with a special shape and a fast leading edge, such as tailored
pulse, is one technique for controlling link processing. The pulse shaping technique is based on light-loop controlled
optical modulation to shape conventional Q-switched solid-state lasers. One advantage of the pulse shaping technique is
to provide a tailored pulse shape that can be programmed to have more than one amplitude value. Moreover, it has the
capability of providing programmable tailored pulse shapes with discrete amplitude and time duration components. In
addition, it provides fast rising and fall time of each pulse at fairly high repetition rate at 355nm with good beam quality.
The regular-to-shaped efficiency is up to 50%. We conclude with a discussion of current results for laser processing of
semiconductor memory link structures using programmable temporal pulse shapes. The processing experiments showed
promising results with shaped pulse.
We report on recent advances in the development of a 1064 nm pulsed master oscillator fiber power amplifier (MOFPA) with integrated modulators enabling programmable temporal pulse shapes and its employment in a tandem photonic amplifier. The MOFPA amplifier chain is seeded by a laser diode operated in the CW regime, yielding very stable spectral characteristics that are independent of the pulse repetition rate and pulse shape. The use of 3 GHz integrated LiNbO3 electro-optic modulators in conjunction with high speed digital electronics results in an excellent pulse shaping capability, a fine pulse amplitude stability and high repetition rate operation (100 kHz-1MHz) with fast rise times (<1ns). Energy per pulse of 8-10 μJ with good beam quality characteristics are obtained using advanced large mode area (LMA) fiber designs in the final power amplifier stage. The output is linearly polarized with a spectral bandwidth of < 0.1 nm. When employed in a tandem amplifier configuration, in which the MOFPA output is input to a single-stage, single-pass Nd:YVO4 amplifier pumped by a single 30 W fiber-coupled 808 nm diode, a 600 mW average power at 100 KHz signal input from the MOFPA was amplified to 6 W with faithful amplification of the input temporal pulse profile while achieving excellent beam quality (M2<1.1) and pulse amplitude stability (< ±3%, 3σ). A model of tandem amplifier performance shows good agreement with experimental results and indicates prospective performance of advanced tandem photonic amplifier configurations.
We report on recent advances in laser processing of solar cells, flexible printed circuit boards, integrated circuit
packages, and semiconductor memory in the nanosecond pulsewidth regime. These process advances are enabled by
innovations in lasers and continue to drive requirements for emerging pulsed solid state and fiber lasers. Demand for
increased throughput is projected to push the pulse repetition frequency for pulsed solid state sources utilized in many of
these applications past 100 KHz. Ongoing device miniaturization continues to enable new applications for visible and
ultraviolet pulsed laser processes, particularly for semiconductor devices. This paper summarizes the current status of
these select laser processes, the laser sources that power them, and the outlook for future innovations in the field.
In this paper, an analytical method, which combines experimental and numerical studies, is reported to determine material properties of Nd: YV04. In the experimental investigation, a laser interferometer is proposed to measure the physical deformation of lasing materials. The numerical solution with the finite-element (FE) method is used to calculate distributions of temperature, stress and strain in the lasing crystal, and then Young’s modulus and Poisson ratio of Nd: YV04 crystal are calculated to be 133GPa and 0.33, respectively.
Digital micro-holo-interferometry is proposed in this paper for microstructure measurements. It is developed based on the in-line digital holography incorporated with long distance microscope. The system structure is theoretically explained with wavefront diffraction analysis. The compatibility of the long distance microscope with the specific requirements in micromeasurement is discussed. And the properties of the in-line configuration in improving system performance are studied. Theoretical analysis of the system is demonstrated by the experiments on a silicon microbeam for deformation determination.
The thermal effects of diode-end-pumped Nd:YVO4 and Nd:YAG lasers are analyzed by a 2-D analytical model and a 3-D numerical model, respectively. The characteristics of the Nd:YVO4 and Nd:YAG rods are comparatively discussed, including temperature distributions and thermal lensing effects. The model quantitatively separates the end effect from the index parts. Under the same pump configuration, we find that the temperature increase in the Nd:YVO4 laser was 2 times larger than those in the Nd:YAG laser, while the thermal lensing coefficient of Nd:YAG was 27% higher than that of Nd:YVO4. We also conclude that a good roundness of the Nd:YVO4 laser beam profile is expected because nearly symmetric thermal lensing in the a and c axes is predicted from our modeling and measurement. Correspondingly, we perform experiments that are in good agreement with theoretical modeling for the thermal lensing of diode-pumped Nd:YVO4 and Nd:YAG lasers.
The control of thermal lensing effect is of importance to scale the output power of diode-pumped solid-state lasers. It is particularly critical for end-pumped systems. In order to reduce the thermal lensing of diode-pumped Nd:YVO4 lasers, we use a composite structured crystal with an undoped end cap of YVO4 attached to the Nd:YVO4 crystal. A numerical model is setup to simulate the temperature, stress, and end bulging of the composite crystal, as well as thermal lensing. The comparisons on thermal behaviors for composite and normal Nd:YVO4 crystals are given in the paper. A diode-end-pumped Nd:YVO4 laser with output power of 15.6W under the pump power of 29W and optical-to-optical efficiency of 54% is demonstrated by using the composite crystal.
Thin films are the elementary structures in many MEMS devices. Their applications can be found vastly in micromachined silicon pressure sensors. With respect to the specific demands in thin film analysis for microstructures, we present a hybrid approach integrating digital microscopic holographic measurement with finite element analysis in this paper for high-resolution full-field characterization of the micromachined silicon thin film. The pressure-induced membrane deflections are accurately measured with the developed system, and serve as reliable reference data to verify the FE model, which is then applied for strain and stress calculation and sensitivity characterization.
A doubly resonant optical parametric oscillator (OPO) was developed with a simple pumping configuration based on our optimized mode-to-pump design. The type II KTA OPO is placed in the cavity of a Q-switched diode-pumped Nd:YLF laser. The linearly polarized Nd:YLF laser at the wavelength of 1053nm generates 6.5 Watts and 11.9 Watts arrange power in TEM00 mode at the repetition rate of 1 and 3 KHz, respectively. We obtain the OPO average power of over 2 Watts with broadband tuning range from 1.7μm to 2.1μm at the repetition rate of 1 to 2KHz. The pulse width is less than 20ns. The maximum OPO energy of 2.5mJ per pulse is obtained at the wavelength of 1.9μm, where the pump energy is 6mJ per pulse and the pump-to-signal efficiency is 42%.
Among the current commercial micromachined devices, pressure sensors are by far the most successful and popular products. They work to sense the displacement-induced stresses of a silicon membrane with the thickness at the micro-scale. The miniature dimension of such devices, coupled with the demand of accurate deflection measurement for performance characterization, make suitable metrological tools in immediate need. In this paper, we present a digital micro-holo interferometric method for realizing highly sensitive measurement of the full-field displacement over the global test structure. Through the analysis on the system principles, the pressure-induced membrane deflection are accurately measured, and further determination of strain and stress is accomplished based on the verified FE model. From the obtained stress-pressure relation, the sensitivity of the pressure sensor is thus characterized.
The imaging capacity of a digital holographic system is studied with space-bandwidth product. The analyses demonstrate that an in-line arrangement can achieve better performance in both the effective field of view and imaging resolution. Furthermore, the effects introduced by the discrete feature of a CCD sensor, characterized by the pixel amount and pixel sensitive dimensions, to the image formation and quality are studied. Comparative discussions are given to the in-line and off-axis geometries respectively.
The thermal effects of diode-pumped Nd:YVO4 and Nd:YAG lasers are analyzed by a one-dimensional model and a three-dimensional model, respectively. The characteristics of the Nd:YVO4 and Nd:YAG rod are comparatively discussed, which include temperature distributions and thermal lensing effect. The model takes into account of index parts and end effect. The theoretical analyses provide a good prediction for the thermal lensing of diode-pumped Nd:YVO4 and Nd:YAG lasers.
The development of a digital micro-holo interferometric system is presented in this paper. With respect to the specific requirements on the microscopic scheme in micromeasurement, application of long distance microscope is introduced with emphasis. With its corporation, the achievable microscopic resolution is studied and demonstrated by the use of the standard resolution test target. Experiments are performed to testify the capacity of the proposed system in resolving structures with lateral dimensions at the micro level. A critical issue, validation of the developed system is also addressed. Aided by finite element analysis and analytical calculation, experimental measurement with the system is addressed. Aided by finite element analysis and analytical calculation, experimental measurement with the system is examined using a hybrid approach. To evaluate the performance of the system, microbeam experiment is presented. Results measured with the system, as well as the numerical simulations are obtained. Quantitative comparisons are carried out in terms of load-induced variations of the test sample, based on which the conclusions are given.
With respect to the two major challenges in micromeasurement, which are high resolution and small object size, digital micro-holo-interferometry is proposed in this paper to provide quantitative information on load-induced variations of microstructures under testing. As primarily measured properties, the obtained deflection-load relationship enables subsequent accurate determination of strain and stress. More importantly, properties of materials in the micro level, which are known different greatly from those of identical bulky ones, can be evaluated based on these experimental input data for computational simulations. Developed upon the in-line configuration and incorporated with long distance microscope, the proposed system can achieve higher imaging performance and resolution capacity. Studies demonstrate that it is capable of realizing accurate measurement to microstructures with lateral dimensions of at least 8 microns. Its applications in characterization of microstructures are experimentally investigated on a micro cantilevered beam as an example. The load-induced deflection is obtained and validated with numerical simulated results based on finite element analysis.
The evaluation of pump capability and scaling output power of vanadate lasers are presented in this paper. With the consideration of thermal fracture limitation and fundamental mode operation, systematic investigations of vanadate crystals are conducted to scale the output power of diode-end-pumped lasers to higher levels. Based on the limitation of pump power, the input-output characteristics and beam propagation factor of vanadate lasers are optimized with the knowledge of thermal effects. The theoretical analyses provide a good prediction to the experiment. A practical example of a single endpumped vanadate laser is demonstrated with cw output powers of 9.8W in TEM00 mode and 12.4W in multimode.
Thermal effects dramatically influence the laser performance of diode-pumped solid state lasers (DPSSL). There are three factors accounting for thermal effects in diode-pumped laser medium: the change of the refractive index due to temperature gradient, the change of the refractive index due to thermal stress, and the change of the physical length due to thermal expansion (end effect), in which the first two effects can be called as thermal parts. A laser interferometer is proposed to measure both the bulk and physical messages of solid-state lasing medium. There are two advantages of the laser interferometry to determine the thermal lensing effect. One is that it allows separating the average thermal lens into thermal parts and end effect. Another is that the laser interferometry provides a non- invasive, full field, high-resolution means of diagnosing such effects by measuring the optical path difference induced by thermal loading in a lasing crystal reliable without disturbing the normal working conditions of the DPSS laser. Relevant measurement results are presented in this paper.
Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency. However, its limited pump volume results in limited output power, usually under 1W. This paper presents a high- efficiency Nd:YVO4 laser end-pumped by a 15W diode laser bar. An optical-optical efficiency as high as 42 percent and an output laser power of over 3W were obtained with a beam quality factor, M2 of less than 1.2 and an output stability of +/- 0.5 percent. Theoretical calculations and experimental data showed that the pumping laser beam was well-matched to the intracavity laser mode.
Thermal effects of diode end-pumped Nd:YVO4 laser are analyzed in this paper. A laser interferometer is set up to determine the optical path difference resulting from thermal effects in crystal under lasing condition. The beam distortions in Nd:YVO4 rod are measured with a He-Ne laser at wavelength of 632.8nm. The changes of interference patterns record the deformation of the rod with increasing pump power. The experimental and theoretical curves of effective thermal focal lengths versus pump power are obtained, and it is found that the theoretical analysis agrees well with experimental measurement. With the analytic results of thermal effects, an optimized resonator is designed to insure that the laser operates in stable mode with an output power of 3.2W, slope efficiency of 52 percent and M2 factor of 1.19.
The numerical modeling on pulse discharge for a high power carbon-dioxide laser was developed to describe and predict laser operating characteristics. The influence of turbulence and convection on the output of a high power fast axial flow carbon-dioxide laser is especially considered in this paper. An obvious requirement is that the pulse has a precisely specified time shape in order to obtain well-controlled optical pulse. The active medium is described by assuming a five-temperature model and balancing the quantum densities of vibrational states of the CO2 and N2 molecules. The conclusions are very helpful to realize pulse operation in cw carbon-dioxide lasers, especially in the laser equipment which is applied to drilling, welding and cutting.
Image hologram is analyzed and comprehended from a new point of view--microcoding patterns of elementary hologram in the paper. The elementary microcoding patterns of image hologram are quantitatively discussed using the elementary analysis method. The mathematic models of the spatial interference patterns of elementary image hologram are established, and the interference fringe patterns on recording plane are studied qualitatively. The purpose and significance of the study is to establish the information coding relationship between the spatial object information (especially position information) and the interference fringe patterns on recording plane correspondently. By analyzing the macroscopic physical meanings of the structural characteristics of interference patterns, the recording and reconstruction mechanism of image hologram are probed deeply into microscopic field.
This paper presents a new phase unwrapping algorithm to deal with the problem of phase restoration from an interferogram that is in presence of both high-level random noise and segmented discontinuity. The algorithm is based on a composite template matching to simultaneously identify unreasonable phase jumps caused by speckle noise and segmented discontinuities such as holes and borders int he wrapped phase map. Examples unwrap with the interferograms generated by the computer and real speckle fringe patterns taken from double-pulsed speckle interferometer are included to show that the technique is efficient and simple to implement.
The characteristics and mechanism of superpulse discharge for high power FAF CW CO2 lasers are based on the rate equation theory. The mathematical modeling analysis of superpulse discharge especially considering the influence of turbulence and convection is simulated on the computer. Detailed mathematical modeling curves which demonstrate how superpulse operation is employed around population inversion, gain and injection power density are obtained. The results are relevant for superpulse CO2 lasers.
The method of multifactorial orthogonal design is proposed in the paper to decide the diffraction efficiency (DE) comprehensively. The orthogonal table is designed to major manufacturing parameters mentioned above. The variance analysis is carried on. The conspicuous factors on DE are obtained, and the optimal technological conditions are established. In addition, regression analysis is also studied to the conclusion, the calculating and experimental results are in good agreement. A fit rate of 81 percent is obtained.
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