II-VI HIGHYAG, a subsidiary of II-VI Inc., is one of the world's leading suppliers in the laser material processing industry. Its innovative laser processing heads and beam delivery systems enable the efficient use of the laser beam for the most dem anding advanced manufacturing applications such as laser cutting, laser welding and laser brazing. www.highyag.com CompanyThe present market of metal laser cutting machines is mainly dominated by laser sources that emit radiation in the wavelength range around one micron. The majority of these lasers generate radiation through pumping of ytterbium doped fiber or ytterbium doped disks, or directly from gallium arsenide (GaAs) semiconductor diodes. The latter direct diode approach has been increasing its market share due to a significant increase of beam quality. A few years ago, high-power direct diode lasers were used for applications where low brightness (BPP between 20 -30 mm mrad @ 4 kW) was sufficient, such as laser brazing and hardening. With the latest improvements in beam quality, reaching 4 mm mrad and below, direct diode lasers are now suitable for laser cutting applications, which are dominated currently by other laser types. This article investigates cutting quality and speed using the II-VI Highyag laser cutting head BIMO-FSC in combination with a direct diode laser. In addition, the machine controlled and independent adjustment of focus position and diameter of the BIMO-FSC have been analyzed in regards to optimization of the piercing process.Typically, laser processing head manu facturers design optical layouts for a rather small wavelength bandwidth in order to avoid the need for broadband coatings that are typically more expen sive and thicker. Increasing thickness of coatings will result in a higher absorp tion and hence higher tendency of focus shift. This is one of the reasons why IIVI Highyag tailored its laser cut ting head BIMOFSC to be used with highbrightness diode lasers. The one used for the investigation is equipped with a 150 mm focal length focusing lens. The combination with a 100 µm fiber ca ble core diameter offers continuous ad justment of spot size ranging from 120 to 320 µm. Furthermore, the wide adjust ment range of the focus position and fo cus diameter offered by the BIMOFSC allows for cutting a broad variety of mate rials with thicknesses up to 25 mm.The investigated cutting tests have been conducted with Teradiode's 4 kW direct diode laser named Terablade. Its wavelength is designed at 970 nm which is shorter than the typical wavelengths of disk lasers (1030 nm) and fiber lasers (1070 nm).Besides different wavelengths, the fiber lasers and diode lasers can differ in beam profile. Fig. 2 shows that both beams have only slight differences at the focus position. Propagating into the near field area, a vast difference in beam profile becomes obvious. While the beam of the fiber laser propagates in a Gaussian like manner, the beam of the diode laser starts to form a TEM 01 mode at two Rayleigh lengths (z R = 5.5 mm for magnification...

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