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LBA - Laser Beam Analyzer In industrial and laboratory applications of CO2 and YAG lasers it is important to know the exact instantaneous distribution of the intensity across the laser beam, i.e. the laser's mode. All the beam analyzing methods known to date are cumbersome and have one serious drawback: they do not allow measurement and continuous monitoring during an experiment or during material processing. The Laser Beam Analyzer - LBA - makes it possible to control the intensity distribution across the laser beam while a work piece is being processed, without noticeable loss of beam intensity. Indeed in CW mode, the intensity is reduced by mere 0.8 %. Working Principle Driven by a synchronous motor, a needle with a high reflective surface rotates in a plane perpendicular to the beam. While passing across the beam it reflects a tiny fraction of the beam onto two pyroelectric detectors. The needle moving at constant speed, the power distribution across the beam section is represented by the amplitude of the amplified signals from the detectors. The LBA is designed for the simultaneous displaying of the intensity profiles in the x and y axes (see picture) on a dual trace oscilloscope. APPLICATIONS 1. Adjustment of CW-Lasers The LBA is mounted and centered on the beam in a convenient position while the oscilloscope is placed beside the mirror to be adjusted. During adjustment the variation of the intensity profile can be directly observed and the laser can easily be adjusted to get an optimum mode. 2. Intensity Profile Control in Material Processing The LBA is permanently installed in an easy accessible place in the beam path between the laser and the work station, the oscilloscope being installed at the work station. This arrangement allows control of the instantaneous mode and power during the working process. The beam intensity loss due to the LBA is 0.8%. Permanent installation in the beam path does not impair production quality. When a laser is used in production - e.g. for steel cutting a "good mode" is a prerequisite for a clean cut. The Laser Beam Analyzer offers permanent control of the intensity profile. Further development toward fully automatic operation is feasible. The signal can be processed electronically and be used for automatic production control by comparison of actual to optimum parameters. There are some interesting aspects to lab application. It is generally known that in metals processing a considerable portion of the radiation is reflected from the metal surface and re-enters the laser via the focusing lens in the form of a parallel beam. This retro reflection increases the power density inside the laser and can lead to a substantial variation of the laser's mode. Direct observation of this phenomenon by means of the LBA allows the optimization of the process parameters. 3. Measurement of Beam Divergence As the rotating needle passes across the beam at constant speed there is a fixed relationship between passage time and beam width. Taking model LBA1 for an example, 400us shown on the CRT screen are equivalent to a beam width of 10mm. By successively installing the Beam Analyzer at different distances from the laser the beam diameter (1/e) can be measured and divergence can easily be calculated from these values. 4. Adjustment of Pulsed-Lasers For pulsed lasers it is suggest able (even not indispensable) to employ a memory oscilloscope. When a laser pulse meets the needle, a very narrow "peak" will appear on the screen in a position corresponding to that of the needle at the pulse instant. As the time goes on, the screen will be filled with many such "peaks", whose enveloping curve represents the laser's mode. To avoid long waiting time with low repetition rate lasers, a synchronization signal is supplied by the LBA to drive a laser pulse when, after every revolution the needle is in a slightly different position. A reset signal is also provided to erase the screen after every scanning. Furthermore the facility of locking the needle across the beam enables the observation of the pulse's time-shape, point-to-point in the beam cross-section. 5. Measurements of Focus The needle's high reflective surface and its moving speed make the LBA suitable for measurement of the focus diameter. The unit is displaced along the beam until the minimum beam diameter has been found. This measurement allows to determine the power density at the focus, as well as the influence of lenses of different focal lengths and shapes. Distorted lenses or mirrors can the be spotted by comparative measurement. SPECIFICATIONS The LBA is available in three different sizes: LBA1 for beam diameter till 25mm; 50(60) Hz scanning rate LBA2 for beam diameter till 40mm; 50(60) Hz scanning rate LBA3 for beam diameter till 60mm; 50(60) Hz scanning rate Detectors window is available either CO2 or YAG laser as well as for both Detectors amplifier is switchable in 4 gains ranges (0.02-1-3-10). The spatial resolution and the sensitivity depend linearly on the chosen gain. o With gain 0.02 the following values are reached: spatial resolution: 4um sensitivity: 0.3mV/sq. mm increasing the gain increase the sensitivity and reduce the resolution of the same factor. Output noise signal is always less than 5mV (rms) Please specify in your order required version and model, detector's window and supply voltage (220 or 110V) and frequency (50 or 60Hz). o Dimension (mm) LBA1 187x89x185 LBA2 293x130x287 LBA3 360x150x355 o o o o o o