A penetration laser welding mode characterized by formation of keyhole is often used. A small portion of the laser beam is reflected back from the keyhole and returned to the laser through the optical system of the welding head and optical fiber. The reflected radiation is monitored in the laser for the safety of the optical resonator and its signal can be read and used for process monitoring. The experiment was conducted to relate the intensity of the back-reflected radiation with depth and width of the weld for the variable focal position. The experiments were performed for two variants of the optical focusing system and materials with different thermo-physical properties - carbon steel and stainless steel. Furthermore, a mathematical model for back-reflected radiation was created using ray tracing. The shape of the keyhole was approximated as an inclined conical cavity. The results of the simulation were compared with experimentally measured data and it was found that the proposed model is most suitable for the description of stainless steel.
Deep penetration welding is a typical industrial application of high power lasers, where plasma can be generated above
the keyhole. Thanks to the plasma plume presence welding process can be controlled on-line by means of the plasma
intensity measurements. Various on-line monitoring methods have been developed in research centers all over the world.
Goal of them is to enable promptly operator action to avoid enormous economical looses if un-expected defect is
detected. Our laboratory was participated in project CLET - “Closed loop control of the laser welding process through
the measurement of plasma” as a responsible partner for developed system testing both in the laboratory with pulsed
Nd:YAG laser and in the real welding facility with high power continual CO2 laser. Control system is based on the
electron temperature computation from the relative intensities of couple of emission lines belong to certain metal ion
present in plasma plume. Our experiment was realized using Ocean Optics HR2000+ spectrometer within the stainless
steel tube longitudinal welding. Several couples of emission lines were tested to acquire a good signal at actual welding conditions. Then power calibration was made to obtain the electron temperature dependence on increasing power. Samples were prepared for microanalysis and measured by laser confocal scanning microscope to find optimal power range for full penetrations achieving without thermal distortion of the tube or weld humping. Numerical model of the remelted area cross section was made to display temperature distribution dependence on increasing power.
Research of the optical radiation interaction with human tooth tissues has started early after the first laser construction.
Absorptivity of the particular tissue is dependent on the wavelength, thus CO2, Er:YAG and Nd:YAG lasers were used in many experimental works all over the world. Near infrared radiation of the pulsed Nd:YAG laser was found to be
suitable for dentine hypersensitivity treatment by sealing of the open tubules with melted and re-solidified dentin. Series
of experiments were performed to find suitable process parameters in the laser laboratory equipped with the industrial
pulsed Nd:YAG laser system. Tooth samples were prepared and classified into five groups according to their different
degree of the surface grinding and polishing. Two types of antireflective agents, erythrosine and black ink, were applied
on the samples surfaces. Coated samples and reference ones without any agents were treated with a set of increasing
pulse energy values. Pulse frequency, pulse length, laser beam diameter on the sample surface and relative speed
remained constant. Lines of the melted spots were displayed by confocal microscope; surface profiles were scanned by
contact profilometer. Dimensions of the dentine melted spots were extracted from the measured data and their
dependence on the laser pulse energy, degree of the surface grinding and type of antireflective agent were evaluated.
In materials engineering, we are often faced with a necessity to display the shape and morphology of studied surfaces.
This is essential for surface evaluation of various components as well as for new materials research. Several imaging
techniques are available for such purposes. One of the most appropriate of them is laser scanning confocal microscopy.
The magnification range of this technique satisfies the needs of researchers working between the limits of conventional
optical microscopes and scanning electron microscopes. It overcomes the limitations of optical microscopy by better
lateral resolution, ability to control the depth of field and possibility of high-resolution 3D imaging of relatively thick
samples. Compared to the more advanced (and more expensive) scanning electron microscopes, laser scanning confocal
microscopy has no special requirement for the sample preparation and there is also no need to measure in vacuum.
Particular examples of laser scanning confocal microscopy beneficial use are presented in this paper. Scratch track
evaluation, diamonds tip control, Tyvek structure examination and measurement of surface characteristics of a wire saw
cut on the glass are reported.
Water Cherenkov detectors are used for studying of high energy cosmic rays. The photomultiplier tubes observe the Cherenkov light generated by fast extensive air shower of charged particles in water. Material trade-named Tyvek is frequently used as the inner lining material of these Cherenkov detectors because a high diffuse reflectivity is required in order to improve light collection uniformity. The results of Tyvek surface microstructure measurement using optical (confocal microscopy) and mechanical (profilometry) methods are presented in this paper. Tyvek surface light scattering anisotropy is commented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.