Fig. 1. A combined laser configuration for intra-cavity phase locking and coherent addition of two transverse multimode laser beam distributions using an interferometric combiner. The light from one channel is directly incident on the beam splitter coating region of the combiner, while that from the other channel is transmitted through the AR coated region, reflected back from the rear surface, and then reflected from the beam splitter coating so as to be collinear with the other transmitted light.

Fig. 2. Experimental arrangement for intra-cavity coherent addition of two transverse multimode laser beam distributions with an interferometric combiner. The two separate transverse multimode distributions were derived from a common gain medium and formed with a double aperture, each of 2.1 mm diameter. The thin film polarizer was used to obtain P polarization in order to minimize losses of the combiner. Optional Q-switch operation was obtained by intra-cavity Q-switch elements.

Fig. 3. A double slit experimental arrangement for confirming the spatially incoherent nature of one transverse multimode laser beam. Two circular pinholes, each with a diameter of 100 μm and spaced 1 mm apart served as slits. The 4-sigma widths of the Gaussian and multimode distributions, at the slits plane, were 1.7 mm and 3.6 mm, respectively. The far field intensity distributions, at the focal plane of the lens, were detected with a CCD array. With the input of Gaussian distribution from a pulsed Nd:YAG laser (M ² = 1.1) a fringe pattern appears at the far field. Whereas with an input of multimode distribution from the same laser (M ² = 4.6), no fringes appear.

Fig. 4. Experimental intensity distributions of the separate transverse multimode channels, and the combined laser output beam distribution obtained using the interferometric combiner. (a) and (b) near and far field intensity distributions of the first channel; (c) and (d) near and far field intensity distributions of the second channel; (e) and (f) near and far field intensity distributions of the combined laser output, using the interferometric combiner.