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.
In this paper, we present the design, fabrication and characterization of the whispering-gallery mode (WGM) miniature sensors for potential use in biosensing at the nanometer scale. In order to understand and investigate the characteristics of WGM resonances, we designed and fabricated a number of sensors with different dimensions. Each sensor is a micro/nano-structure consisted of a microdisk as the resonating cavity and a micro waveguide for light delivery and collection. In addition to the waveguides having uniform cross-section dimensions, tapered waveguide was also considered in our studies. A simulation model was employed to characterize the EM field and radiation energy density of the designed sensors. The gap effects on WGM resonance in terms of quality factor and full width at half maximum (FWHM) were evaluated. Following the design and characterization, the sensors were fabricated in 1.3μm-thick Si3N4 film using 248nm optical lithography and conventional silicon IC processing. Top and down SEM measurements of the fabricated sensors were conducted and the data for the sensors in one device are given.
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 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 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 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.
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.
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.