Stellar population studies in the infrared (IR) wavelength range have two main advantages with respect to the optical regime: they probe different populations, because most of the light in the IR comes from redder and generally older stars and allow us to see through dust because the IR light is less affected by extinction. Our project investigates the sensitivity of various spectral features in the 1-5um wavelength range to the physical properties of stars (Teff, [Fe/H], logg) and aims to objectively define spectral indices that can characterize age and metallicity of unresolved stellar populations. We implemented a method that uses derivatives of the indices as functions of Teff, [Fe/H] of log g across the entire available wavelength range to reveal the most sensitive indices to these parameters and the ranges in which these indices work. Here, we complement the previous work in the I and K bands reporting a new system for Y, J, H and L atmospheric windows. We list the equivalent widths of these indices for the Infrared Telescope Facility (IRTF) spectral library stars.