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Broad area type-I GaSb based diode lasers have recently exceeded 100 mW continuous wave room temperature powers in 3.1-3.2 m spectral region. Certain applications such as single frequency sources for spectroscopy and efficient coupling to single mode fiber require single lateral mode laser operation. We characterize and compare two types of lasers with similar structures and various ridge widths emitting at 3.1 and 3.2 m. We obtain 35 and 25 mW of continuous wave single lateral mode power from 8 and 13 m wide ridge lasers emitting at 3.1 and 3.2 m respectively. This constitutes a threefold improvement compared to the previous result. Both devices had ridges etched to the depth leaving approximately 300 nm of the top p-cladding in the areas outside the ridges. For 3.2 m emitting lasers the dielectric thickness was 220 nm while it was 510 nm for 3.1 m emitting lasers. Gain spectra were measured by Hakki- Paoli technique for various ridge widths. From gain spectra we extract differential gain and internal loss. We find that the internal loss in thin dielectric, 3.2 m emitting laser is about 14 cm-1while it is 7 cm-1in thick dielectric, 3.1 m emitting laser for the ridge widths of 13 and 8 m exhibiting single lateral mode operation respectively. Internal losses measured on broad area, 100 m wide lasers processed from the same materials are similar and around 6-7 cm-1. We discuss reasons for the internal loss increase with the aid of simulation of optical mode field and loss in our waveguide structures.