Thermal tuning of volume Bragg gratings for spectral beam combining of high-power fiber lasers

Abstract

High-radiance lasers are desired for many applications in defense and manufacturing. Spectral beam combining (SBC) by volume Bragg gratings (VBGs) is a very promising method for high-radiance lasers that need to achieve 100 kW level power. Laser-induced heating of VBGs under high-power radiation presents a challenge for maintaining Bragg resonance at various power levels without mechanical realignment. A novel thermal tuning technique and apparatus is presented that enables maintaining peak efficiency operation of the SBC system at various power levels without any mechanical adjustment. The method is demonstrated by combining two high-power ytterbium fiber lasers with high efficiency from low power to full combined power of 300 W (1.5 kW effective power), while maintaining peak combining efficiency within 0.5%.

Development and Thermal Management of kW-Class High-Power Diode Laser Source Based on the Structure of Two-Stage Combination

“…5, we can observe that VBG 1 combines two channels, however, VBG 4 combines four transmitting channels and one diffracting channel. Given that commercially available PTRglass-based VBGs have a thermal expansion coefficient as low as 10 −5 /K [18], so the thermal stress on the VBG is not a major factor to be considered. Unfortunately, VBGs are temperature dependent elements which have a wavelength shift coefficient of approximate 0.01 nm/K.…”

Influence of laser array performance on spectrally combined beam

“…The spectral width of the combined beam is associated with the total length of the LA according to Equation (6). Figure 13 shows the variations of the spectral width of the combined beam with the total length of the LA for different focal lengths.…”

“…Fortunately, beam combining offers an effective solution to the laser system design at multi-kW level (3,4). Recently, incoherent spectral beam combining (SBC) has been approved to be a robust and simple technique for achieving high-power laser by combining multiple beams from laser arrays (LAs) into a single beam (5)(6)(7)(8). An array of emitters are placed in an external cavity which is composed of a transform lens, a diffraction grating and an output coupler (see Figure 1).…”

Influence of transform-lens focal length on spectral beam combining in an external cavity with a microlens array

“…High-brightness lasers have significant applications in defense and manufacturing [1][2][3]. Spectral beam combining (SBC) is a wellestablished method for high-radiance lasers that can achieve 100 kW level power [4][5][6][7].…”