Lasers and Holograph pre lab abstract In an ideal laser, transitions of excited atoms will produce photons of a single wavelength with perfect coherence. Due to different longitudinal modes in the laser cavity and Doppler broadening, the laser light produced will have a band of wavelengths resulting in a finite coherence length. We will measure the coherence length and beat frequency of a HeNe laser. A photodetector and oscilloscope will be used to observe beating. The FFT function of the oscilloscope will provide information about the frequency difference between modes, which can be used to estimate the lasers coherence length. Another way to measure coherence length is by using a Michelson Interferometer. By analyzing the contrast of interference fringes at varying path length differences between mirrors, the coherence length can be determined. We will also explore the holography process by making several holograms. Two temporally and spatially coherent light beams (object and reference) from the HeNe laser will be used to acquire both the intensity and phase of the reflected light from the object. The two beams will interfere at the holographic film, producing interference patterns that will reconstruct the 3D image of the object when illuminated by a laser beam identical to the reference beam.