period detection for a series of photons
As discussed in the comments to your question the recorded data that consists of arrival times of photons must first be converted to photon counts $n$ for this is the light intensity. The result of this conversion will be a vector $n(k)$ (with discrete time $k$) that represents the evolution of light intensity over time and that can be analyzed in more detail with an FFT, for example. The Lomb-Scargle method won't help here as you'd like to analyse light intensity, not photon arrivals. It could be of use if your data was a sequence of unequally space light intensity values. But as I understand your question this is not the case.

In order to obtain $n(k)$ count the number of photon arrivals in every time interval $t_0 + kT$, where $t_0$ is some constant time offset (e.g. first arrival time) and $T$ is the length of the equidistant time intervals. $T$ determines the sampling frequency $f_\mathrm{s} = 1/T$ of $n(k)$ and consequently the range of any spectral analysis, that is $0 \ldots f_\mathrm{s}/2$. On the other hand $T$ should be sufficiently large to obtain a reliable photon count in each time interval.

To analyse the periodicity of $n(k)$ calculate its FFT and look for distinct peaks. Functions like periodogram also come handy sometimes.