Continuous monitoring of high power (above 2 kW) CO2 laser beams with camera based systems has not been effective because beam sampling optics have not been available. Camera based systems allow real-time imaging of the entire beam profile which in turn enables real-time tuning and alignment of the laser, as well as enabling instantaneous recognition of beam misalignment in the optical delivery train. Spiricon and II-VI have jointly developed a new method
for in-line, passive sampling and beam profiling of high power, multi-kilowatt CO2 lasers. The system uses conventional optics in a novel sampling arrangement, coupled to a Spiricon Pyroelectric IR Camera and Laser Beam Analysis
software.
The approved Draft International Standard 11551 on test methods for absorptance of optical laser components recently passed the international voting procedure. The utility of this standard practice document is the subject of the present round robin test. In order to cover a broad range of CO2-laser optical components, different types of metal mirrors and transmissive ZnSe-optics were included in the master sample set. After an initial inspection, this set passed through a series of optical laboratories in the United States, the United Kingdom, and Germany. The absorption of the samples was measured by calorimetric methods according to ISO DIS 11551, and the measurement results were compiled by the coordinating institute. The evaluation of the experiment was not started until all tests were completed. The results of the round robin test are discussed, compared and evaluated with respect to ageing mechanisms in optical coatings for CO2-laser systems. Although a great variety of different test facilities was employed by the round robin partners, a good agrement of the absorption values was observed for the wavelength of 10.6 micrometers . This demonstrates the versatility of the approved Draft International Standard 11551 for the calorimetric measurement of optical absorption in CO2-laser components.
Birefringence is an important factor in determining the imaging quality of visible and infrared optical systems. This paper presents residual birefringence data obtained at 0.6328 micrometers and 10.591 micrometers from several ZnSe and multispectral grade ZnS windows. Refractive index inhomogeneity tests were also performed on the samples at 0.6328 micrometers and their results are given. Residual birefringence data at 0.6328 micrometers is compared to data at 10.591 micrometers .
Single shot laser damage studies have been performed using an RF-excited long pulse laser and a TEA-CO2-laser with pulse durations of 1.2 ms and 100 ns, respectively. Besides bare diamond turned copper mirrors with different metal and dielectric coatings, ZnSe-optics with selected coating types were tested. The temporal damage behavior in the long pulse regime was investigated on the basis of a damage detection system with a time resolution of 10 microsecond(s) . The dependence of the damage threshold on the intensity is discussed in consideration of the integral absorptance of the coatings. The measured damage thresholds of this detection system are compared to those obtained by Nomarski/darkfield microscopy. The local variation of the laser induced damage threshold is correlated to the corresponding photothermal deflection signal, reflectance, and defect density of the coated surfaces.
Industrial high power CO2-laser manufacturers strive for the utmost in reliability of their lasers. Since physics is limiting the intrinsic absorption values of optics it is most important to focus on the surface absorption mechanisms which are not yet well understood. AFM techniques are suitable for further investigation into surface related absorption phenomena.
KEYWORDS: Reflectivity, Absorption, Finite element methods, Optical coatings, Thin film coatings, Chemical lasers, High power lasers, Laser optics, Dielectrics, Copper
With the output power of CO2-Lasers still increasing, the optimization of optical components becomes even more important. In todays high power lasersystems the optics have to withstand power densities of typically 1 kW/cm2 and more, thus absorption has to be kept at a minimum. If not, problems such as distortion of the optical surface, loss of mode control, loss of output power, thermal focusing in the output beam or even damage to the whole system might occur.
Cadmium telluride is the primary choice for electro-optic modulator applications in the mid infrared region
- particularly at 10.6 micron. In principle, single crystal CdTe in the rest state is only weakly birefringent along the
{1 1O} planes. Some internal birefringence does exist, however, due to fabricated-in stress birefringence and
birefringence associated with slippage of the crystal along the {1 1 1} planes. When a voltage is applied to a CdTe
crystal, the total phase shift introduced by the crystal is a result of the combination of the electro-optic effect and the
residual birefringence. This paper will present a method of measuring the phase shift produced by residual birefringence
in CdTe modulators at 10.6 micron. The test method is a modification of the crossed polarizer technique. Test results
will be presented for CdTe modulators with voltage and without voltage.
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