There is a need for high-power narrow-linewidth, small footprint, highly coherent diode lasers at various wavelengths (400-1800 nm) that can be utilized in many areas of photonics including fiber laser seeding, remote sensing, biomedical imaging, atomic clocks, quantum computing, THz spectroscopy, Raman spectroscopy, optical trapping, etc. Volume Bragg Grating (VBG) stabilized Fabry-Perot (FP) semiconductor lasers offer a versatile and robust platform for these applications. A Scanning Fabry-Perot Interferometer (FPI) is implemented for in-situ VBG alignment for these hybrid external cavity lasers (HECLs) in high volume production. Utilizing this method, it is possible to isolate a Single Longitudinal Mode (SLM) of a single spatial mode semiconductor laser with very narrow linewidth. The typical laser linewidth during the production process is measured to be 0.01 nm with an Optical Spectrum Analyzer (OSA) and a few MHz with the FPI, both of which were limited by the resolution of the instrument. However, the actual linewidth of these high-power lasers (up to 450 mW fiber-coupled and 600 mW free space) are measured in final testing using the heterodyne beat note method. These measurements show that these VBG-locked single spatial mode FP lasers have Lorentzian linewidth of less than 100 kHz. The result of narrower laser linewidth is achieved due to the effect on the external cavity feedback and the increased cavity length. The linewidths of these wavelength stabilized lasers between 633 nm and 1064 nm are presented here and the input of the isolator, laser driver electronics and temperature controller on linewidth are studied and discussed as a function of optical power, laser temperature, and wavelength.
KEYWORDS: Semiconductor lasers, Diodes, Laser applications, Laser processing, Reliability, Fiber lasers, High power lasers, Control systems, Laser welding, Fiber coupled lasers, High power diode lasers
High-power diode lasers are nowadays well established manufacturing tools in high power materials processing, mainly for tactile welding, surface treatment and cladding applications. Typical beam parameter products (BPP) of such lasers range from 30 to 50 mm·mrad at several kilowatts of output power. TRUMPF offers a product line of diode lasers to its customers ranging from 150 W up to 6 kW of output power. These diode lasers combine high reliability with small footprint and high efficiency. However, up to now these lasers are limited in brightness due to the commonly used spatial and coarse spectral beam combining techniques. Recently diode lasers with enhanced brightness have been presented by use of dense wavelength multiplexing (DWM). In this paper we report on TRUMPF’s diode lasers utilizing DWM. We demonstrate a 2 kW and a 4 kW system ideally suited for fine welding and scanner welding applications. The typical laser efficiency is in the range of 50%. The system offers plug and play exchange of the fiber beam delivery cable, multiple optical outputs and integrated cooling in a very compact package. An advanced control system offers flexible integration in any customer’s shop floor environment and includes industry 4.0 capabilities (e.g. condition monitoring and predictive maintenance).
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