Dual-Wavelength Passively Q-Switched Erbium-Doped Fiber Laser Incorporating Calcium Carbonate Nanoparticles as Saturable Absorber

This study experimentally demonstrates the operation of a dual-wavelength passively Q-switched erbium-doped fiber laser that incorporates CaCO3 nanoparticles as a saturable absorber (SA). The SA was prepared by using the drop-casting method, wherein CaCO3 nanoparticles were embedded in a polyvinyl alcohol (PVA) polymer to form a CaCO3/PVA film SA. The film was integrated into a ring laser cavity with a 976 nm pump to generate Q-switched pulses. The properties of the SA were examined experimentally, and its modulation depth is approximately 47%. As the pump power increased from 180 mW to 270 mW and the pulse repetition rate increased from 12.67 kHz to 21.3 kHz, the corresponding pulse width decreased from 35.27 μs to 18.74 μs. The signal-to-noise ratio was approximately 25 dB, highlighting the laser’s stability. The results indicate that the proposed CaCO3/PVA SA is suitable for realizing portable Q-switched lasers

Preparation of GaN/Porous silicon heterojunction photodetector by laser deposition technique

Abstract In this work, gallium nitride (GaN) thin film was deposited on porous silicon (PSi) substrate via a pulsed laser deposition route with a 355 nm laser wavelength, 900 mJ of laser energy, and various substrate temperatures raging from 200 to 400 °C. The structural and optical properties of GaN films as a function of substrate temperature are investigate. XRD studies reveal that the GaN films deposited on porous silicon are nanocrystalline with a hexagonal wurtzite structure along (002) plane. The photoluminescence emission peaks of the GaN/PSi prepared at 300 °C substrate temperature are located at 368 nm and 728 nm corresponding to energy gap of 3.36 eV and 1.7 eV, respectively. The GaN/PSi heterojunction photodetector prepared at 300 °C exhibits the maximum performance, with a responsivity of 29.03 AW−1, detectivity of 8.6 × 1012 Jones, and an external quantum efficiency of 97.2% at 370 nm. Similarly, at 575 nm, the responsivity is 19.86 AW−1, detectivity is 8.9 × 1012 Jones, and the external quantum efficiency is 50.89%. Furthermore, the photodetector prepared at a temperature of 300 °C demonstrates a switching characteristic where the rise time and fall time are measured to be 363 and 711 μs, respectively