Degradation of beam quality and depolarization of the laser beam in a step-index multimode optical fiber

Single‐shot thermometry using fiber‐based picosecond coherent anti‐stokes Raman scattering (CARS) spectroscopy

“…The degree of polarization of the Stokes and pump beams is found to be nearly independent of the input‐pulse energy. The observed exponential dependence of the degree of polarization of the output beam on fiber length is similar to that reported by Zhan et al . The degree of beam polarization degrades exponentially with an increase in fiber length because of the increase in birefringence disturbances and mode coupling caused by external mechanical stresses such as bending and fiber‐structure inhomogeneity .…”

“…The observed exponential dependence of the degree of polarization of the output beam on fiber length is similar to that reported by Zhan et al [24] The degree of beam polarization degrades exponentially with an increase in fiber length because of the increase in birefringence disturbances and mode coupling caused by external mechanical stresses such as bending and fiber-structure inhomogeneity. [24] Because the broadband Stokes laser experiences higher chromatic dispersion in the fiber, those depolarization effects become more prominent and, hence, further depolarize the Stokes beam. [29] The observed pseudo-randomly polarized excitation-laser beams are thought to cause a reduction in CARS signal generation.…”

“…Taking the above criteria into consideration, we characterized the fiber transmission of the narrow‐band pump (linewidth ~0.2 cm −1 at 532 nm) and broadband Stokes beams (linewidth ~135 cm −1 at 680 nm). The experimental setup and method used for the fiber‐transmission test are described elsewhere; MSIFs (OFS Model HCG‐M0365T) were used in this study. In our measurements, the shorter length fibers (0.3 and 1 m) tested were nearly straight, and the longer length fibers (3 and 6 m) were tested at a bending radius of ~30 cm.…”

“…For each fiber length, the average power for the two orthogonal polarization directions was measured. The polarization modulus V of a laser beam measures the degree of polarization of the beam and is defined by the equation V = [ P y ( L ) − P x ( L )]/[ P y ( L ) + P x ( L )]; here, V = 1 and V = 0 indicate a completely polarized and an unpolarized beam, respectively. By monitoring the signal while rotating the polarizer at the output of the fiber, we confirmed that the discrepancy between the two polarization components results mainly from the depolarization effect, not polarization rotation.…”

Monitoring of welding status by molten pool morphology during high-power disk laser welding

“…High power laser beam has excellent beam quality, more homogeneous distribution of temperature, and lead to minimal distortions of specimen when it is applied in hot working and manufacturing [1][2][3]. Welding technology with high-power disk laser beam, as a high quality joining technology, is widely applied in many fields, such as automotive industry and manufacturing [4][5][6].…”