Coherence Length Measurements of Low-cost Lasers*

Interference fringes offer a striking demonstration of wave mechanics with widespread utility. Within this realm, laser pointers such as those marketed for presentation remotes, toys, and amateur astronomy devices offer an intriguing possibility of being used on account of both their low cost and relative ease of accessibility. In spite of this promise, the coherence lengths of low-cost lasers are often not reported, limiting their potential utility. Here we present a systematic characterization of these properties using a home-built interferometer featuring a fixed-length arm on one side and a variable-length arm on the other side enabled by a motorized translation stage and retroreflecting corner cube. To date, we have measured the properties of a Logitech R800 presentation pointer remote, utilizing a green diode laser as its optical element. We found multimode behavior, with coherence lengths still visible out to roughly four centimeters in optical path difference. Our results provide crucial data on the viability of these low-cost sources for applications in pedagogical contexts and industry, facilitating the construction of affordable interferometric devices.