研究目的
To characterize both nonlinear refraction and absorption in a vertical-external-cavity surface-emitting laser (VECSEL) as a function of pump irradiance over the whole range of lasing wavelengths and understand self-modelocking of VECSELs driven by nonlinear lensing.
研究成果
The study concludes that both nonlinear absorption and refraction decrease with increasing pump irradiance, consistent with prior investigations. These findings may help better understand the phenomenon of self-modelocking in VECSELs and facilitate their future design and application.
研究不足
The study acknowledges the presence of systematic uncertainty in the absolute value of n2 due to the contribution of the heat spreader and the inability to completely exclude thermal effects from n2 measurements. The relative pump-dependent trends are not influenced by probe-induced thermal heating of the sample.
1：Experimental Design and Method Selection:
The study uses the Z-scan technique in reflection geometry to probe the nonlinear response of the gain chip over its whole lasing wavelength range. A wavelength-tunable, modelocked Ti:sapphire laser is used for probing.
2：Sample Selection and Data Sources:
The gain chip of the (InGa)As/Ga(AsP) material system is used, mounted with an intracavity silicon carbide (4H SiC) heat spreader.
3：List of Experimental Equipment and Materials:
Equipment includes a wavelength-tunable, modelocked Ti:sapphire laser, a frequency-resolved optical-gating (FROG) device, neutral-density filter wheel, lens of 30 mm focal length, Peltier element, and water cooling system.
4：Experimental Procedures and Operational Workflow:
The probe beam is focused on the gain chip on a translation stage. Z-scan measurements are performed at a heat sink temperature of 18°C with optical pumping applied.
5：Data Analysis Methods:
The extraction of nonlinear refractive index n2 and nonlinear absorption coefficient β follows the procedure described in Ref. [19], using linear relationships to deduce values from probe irradiance.
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