Nonlinear reflectivity of AlGaInP SESAMs for mode locking in the red spectral range

Area of Science:

• Optics and Photonics
• Semiconductor Physics
• Laser Technology

Background:

• Mode-locked vertical external-cavity semiconductor lasers (VECSELs) offer wavelength versatility.
• Semiconductor saturable absorber mirrors (SESAMs) are crucial for pulsed emission and pulse property control in VECSELs.
• Characterizing SESAMs is essential for optimizing VECSEL performance.

Purpose of the Study:

• To characterize Gallium Indium Phosphide (GaInP) quantum well SESAMs.
• To determine saturation fluences and modulation depths for SESAMs with varying numbers of quantum wells.
• To investigate the performance of SESAMs within a home-built mode-locked VECSEL.

Main Methods:

• Utilized a nonlinear reflectivity setup in the red spectral range (~660 nm).
• Employed a home-built mode-locked VECSEL to achieve high fluence (up to 430 µJ/cm²) with chirped pulses (7.5 ps).
• Performed first-of-its-kind characterization of GaInP quantum well SESAMs.

Main Results:

• Determined saturation fluences of 38 µJ/cm² (one quantum well) and 34 µJ/cm² (two quantum wells).
• Measured modulation depths of 5% and 10.3% for SESAMs with one and two quantum wells, respectively.
• Identified a consistent nonsaturable loss of 2.8% across all structures, attributed to scattering.

Conclusions:

• Successfully characterized GaInP quantum well SESAMs, providing critical data for VECSEL design.
• The study highlights the impact of quantum well number on SESAM performance parameters.
• Scattering loss is a significant factor contributing to nonsaturable loss in these SESAMs.