A compact, all passive optical design laser beam analyzer has been developed which can analyze a focused laser beam from a CO2 laser with a wavelength range of 9.4 microns to 10.6 microns and provide real time M-squared, spot size, astigmatism, beam divergence, Rayleigh length and focal position values. The instrument utilizes a special Fabry-Perot resonator and a bolometer sensor which provides a complete beam waist caustic in real time. The unique optical design further incorporates a novel method for adjusting attenuation without the need to implement neutral density filters. The adjustability of the Fabry-Perot resonator provides the means to measure a wide range of focal lengths and very long Rayleigh lengths.

Monitoring both near and far field laser beam parameters is extremely helpful in understanding the quality of a laser process. The measurement of such parameters has not been practical to date due to the required disruption of the process beam in order to make the measurement. A significant quality control enhancement could be realized if one could monitor both near and far field patterns of the laser system during the process if it could be done with minimal loss or alteration of the process beam. A novel optical design is discussed that integrated into a laser process head with minimal power loss and disruption to the Laser beam. This in-line monitoring system provides focal spot size, Rayleigh length, focal position and M- squared values as well as all the other ISO beam profiling parameters in real time. An in-line laser beam monitoring system makes possible a higher level of quality control and reduced scrap thereby providing a higher level of reliability to laser processing.

Selection of optics and their alignment are too often taken for granted in the design and building of a laser material processing system. Traditionally the “measuring stick” is the process and whether it is working and not necessarily a quantitative value on the spot size and whether it has any aberrations. It is quite possible to have good optics and poor alignment and conversely have poor optics and good alignment and not immediately know that there is a problem at the process. Beam quality metrics have been around and in use for decades but have tended to be too bulky, expensive and hard to use for the average user. We study the impact of alignment and quality of typical optical components in a laser material processing system and the resulting impact at the focal spot. The consequence of decenter, tilted optics and commonly used beam enhancement devices like beam expanders are quantitatively investigated. The common optical aberrations of coma, astigmatism and spherical aberration are illustrated and correlated to the common alignment and optical selection mistakes. The importance of measuring the laser beam in both the near and far field using an all passive optical design beam metric system is further outlined.

The majority of methods available for measuring the M-square or the beam parameter product of a laser employ a time averaging technique based upon the ISO 11146-1 beam metric standard. In the ISO standard five points must be measured within the first Rayleigh range to establish the beam waist and another five points measured beyond the second Rayleigh range to obtain the asymptote from the corresponding hyperbolic fit of the minimum ten data points measured. Other real time, i.e., instantaneous M-square methods exist but do not fully comply with the ISO 11146-1 standard to the exact letter of the document. One measurement technique is able to view three Rayleigh lengths in real time but due to gain and area limitations of the sensor, the third Rayleigh range is hard to measure to the full extent of the ISO standard or only can be under limited conditions. It is therefore desirable to have a technique that complies with the ISO standard and provide real time M-square or beam parameter product values. We present a technique that simultaneously measures outside the second Rayleigh range while at the same time measure the first Rayleigh range where the gain of the two regions are optimized and there is sufficient area available on the sensor to comply with the ISO standard.