We have developed an interferometer for gauge block calibration based on phase shifting evaluation. The measurement
process can provide flatness, parallelism and longitude. The employed wavelengths need to be corrected according to the
refractive index of the air the light beams passes through. In our case, this correction is obtained indirectly using readings
of temperature, pressure and relative humidity taken by high resolution sensors. To preserve stability, the interferometer
is encapsulated in a chamber with active temperature control. The design, measurement principle, calibration, stability
and reproducibility are analyzed. Since one of our goals is to employ robust and cheap diode lasers as light sources, this
paper describes also the system we are developing to carry out a red diode laser stabilization using a mode locking
technique. The instruments and assembly employed to avoid the Doppler effect in the gas cells, which limit wavelength
resolution, are described as well. Several experimental tests have been carried out that show the great susceptibility of
this assembly to changes in environmental conditions, which affect the iodine cell's absorption spectrum.
A new system for characterizing the flow delivered by a Laval nozzle in different stream configurations has been designed, developed, settled and tested. An optical module (Mach-Zehnder interferometer), an acquisition module (CMOS camera) and a processing module (Fourier Transform Phase Difference Method) have been integrated and
assembled in order to obtain the instantaneous optical phase distribution along the gas flow. An additional postprocessing
numerical stage provides gradient and Laplacian information of the optical phase distribution and allows a complete modeling of the fluid flow. In this work the main results, advantages and limitations of the metrological protocol related with a detailed measurement campaign are presented. Also the analysis of the obtained optical phase difference distribution is compared with results given by a tailored processing numerical stage.
Narrowband ultrasonic surface acoustic waves are of the greatest current interest for the nondestructive testing of thin-walled members and shell structures like plates, pipes, bridge girders, cans and many others. The measurement and characterization of ultrasonic displacement fields of Lamb waves by pulsed TV holography (TVH) is presented. Narrowband ultrasound is generated in a few millimeters thick aluminum plate by the prismatic coupling block method using a tone-burst excitation signal in the range of 1MHz. At this frequency, the plate supports only a few Lamb wave modes, mainly the A0 and S0 ones. The simultaneous presence of these modes produces a beating clearly detectable as a spatial amplitude modulation. Our self-developed TVH system performs the optical phase evaluation by the Spatial Fourier Transform Method and renders the instantaneous out-of-plane mechanical displacement field along the whole inspected area. From this field, the wavenumber of each Lamb mode can be obtained and, by combining them with the value of the ultrasound frequency and with the Rayleigh-Lamb theoretical frequency spectrum, information about the elastic constants of the specimen material is obtained.
The role of the assist gas blown by a nozzle during the laser cutting process of ceramics is very important as a complex flow field is created by the interaction with the material. Flow visualization provides valuable information related with the properties and characteristics of the process in order to clear up misconceptions and as a first step towards the nozzle optimization. Optical methods as Schlieren or interferometry are suitable techniques for this task as well-known non-intrusive full-field methods utilized for analysing fast transient flow phenomena. In this work a Mach-Zehnder interferometer is employed in order to characterize a Laval nozzle by studying the shock wave patterns in a free gas jet as a previous step in order to study the complex interaction of the gas flow against a transparent model of the processed material. The optical phase is extracted from the obtained high-frequency fringe pattern by the Fourier Transform Phase-Difference Method. Disturbing effects are cancelled by proper combination of high-frequency fringe patterns obtained with and without gas flow. The shock wave pattern is analyzed for different geometrical configurations and operating pressures.