Thanks guys for your precious response.
About the nature of our collaboration, my work was in the area of Chemistry and we indeed found and established new application areas for their developed systems. It was like merging two areas by expanding the utilization of their materials into new chemical reactions. As a result, we did some back-and-forth and discussions during the work. So, as you put, I think it would be good for me to get a letter of recommendation from him focusing on the output of our work.
Thank you again for your commentary.