I. INTRODUCTION In the last decade, with increased energy and momentum resolution, angle resolved pho- toemission spectroscopy (ARPES) has emerged as a powerful probe of the mass renormaliza- tions, or ”kinks”, in the electron spectral function associated with the coupling of electrons to collective excitations in condensed matter systems. 1 In particular in many systems it has been possible to clearly identify the coupling to phonons, spin waves and charge density waves. 1 In the high T$_{c}$ cuprates on the other hand the identification of the modes responsi- ble for the observed mass renormalizations has often proved controversial, particularly when different modes occur at the same energy. Experimentally a mass renormalization and asso- ciated kink in the dispersion at 70 meV 2 has been attributed to either spin excitations 3 or to phonons $^{4}$. However a recent theoretical study5 has suggested that coupling to phonons in the 70 meV energy range and above is, by itself, too small to produce the observed mass renor- malization. A mass renormalization observed at 350 meV has also attracted considerable attention but again that exact region remains controversial $^{6}$. In the present communication, using laser based photoemission 78 we present evidence for an additional kink in the nodal region of optimally doped Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212, T$_{c}$ =91 K). We demonstrate that this new kink at low energies exhibits a unique dispersion with respect to the superconducting gap in the nodal region of the Brillouin zone. That is, it always appears 8 meV below the superconducting gap regardless of the gap’s magnitude. Because of this behavior we can unequivocally associate an observed mass renormalization in a high T$_{c}$ cuprate with a single phonon mode. The ARPES study was carried out with a laser based 6 eV photon source produced as the fourth harmonic of a mode-locked Ti:Sapphire oscillator. The oscillator emitted transform limited pulses of 2 ps duration at a repetition rate of 105 MHz. The spectral width of the fourth harmonic beam was confirmed to be less than or equal to 2.5 meV FWHM with a deep ultraviolet imaging spectrometer at the limit of its resolving power. The 6 eV photon beam was focused onto the sample with a 100 mm focal length VUV grade CaF 2 lens. The sample, a high quality, single crystal of optimally doped Bi2212, was cleaved in situ at a II. EXPERIMENTAL METHODOLOGY 2