Lateral-gradient laser spike annealing (lg-LSA) has been developed for high-throughput materials characterization, providing unique capability to investigate materials’ properties at high temperatures within the sub-millisecond time regime. However, it is difficult to laser process highly reflective thin films (HRTFs), such as metals and alloys, due to limited laser energy absorption. Additionally, composition-dependent reflectivity makes it challenging to achieve consistent temperatures when composition spreads are analyzed. To address these challenges, we have developed an innovative “Universal Substrate” to complement lg-LSA for HRTFs. This technique is based on irradiation of samples from the backside through a transparent substrate, such as glass or Al2O3, with light absorbed by a tungsten absorber thin film. A silicon nitride barrier separates this tungsten layer from the actual films of interest. By reversing the geometry, the laser incident from the substrate side is absorbed by tungsten and heats the surface film by conduction. The effectiveness of this technique was demonstrated using a metal-oxide compound, Bi2O3, and a Nb-Si binary compositional-spread library. Phase formation sequences, starting from amorphous, were analyzed over a range of laser powers and for timescales of 2 ms to 6 ms. Multiple structural transformations, including δS, β, and δL in the Bi2O3 system, as well as Nb3Si (Pm3 ̅m), Nb3Si (Pm3 ̅n), and Nb8O21 (Pbam) in the Nb-Si library, were characterized using optical microscopy, optical reflectance spectroscopy, and X-ray diffraction. This novel technique enables lg-LSA to anneal arbitrary films irrespective of their optical properties, facilitating the investigation of a wide range of material systems in the future.