Laser beam characteristics using dc-induced second harmonic generation.

Area of Science:

• Nonlinear optics
• Laser physics
• Beam characterization

Background:

• Electric field induced second harmonic generation (EFISHG) is a nonlinear optical process.
• Previous studies noted a discrepancy between confocal parameters derived from EFISHG intensity profiles and beam diameter measurements.
• This discrepancy suggested potential issues with laser beam quality or measurement techniques.

Purpose of the Study:

• To identify the cause of the disagreement in confocal parameter calculations for laser beams.
• To demonstrate that deviations from the pure Transverse Electric and Magnetic (TEM(00)) mode are responsible for the observed discrepancy.
• To provide a method for accurately characterizing laser beams with non-ideal mode structures.

Main Methods:

• Utilized experimental beamscan data to analyze laser beam profiles.
• Expanded distorted laser beams into their component modes.
• Calculated the second harmonic generation (SHG) profile based on the mode expansion.
• Compared calculated SHG profiles with experimental observations.

Main Results:

• Confirmed that the departure of a laser beam from the pure TEM(00) mode causes the discrepancy in confocal parameter calculations.
• The mode expansion method accurately predicted the second harmonic intensity profile for distorted beams.
• The calculational procedure using mode expansion showed consistency with experimental observations.

Conclusions:

• The assumption of a pure TEM(00) mode is critical for accurate laser beam characterization using SHG.
• Deviations from the TEM(00) mode necessitate advanced analysis techniques, such as mode expansion, for precise optical measurements.
• This work provides a validated method for understanding and correcting for beam distortions in nonlinear optical experiments.