Important steps in the evolution of the technique and algorithms have been: the acquisition through endoscopic device [COQ95, SCHE99, SCHE01, KOLE03, PED03], the use of high wavelength [ALL03], and short-coherence laser source [CUC97, IND00, PED01a, PED02, MAS05, MAL05]. A very important step was the retrieval of the phase information in addition to the amplitude. Different techniques exist to reconstruct the phase. In-line techniques require phase-shifting procedures performed either by several successive hologram acquisitions [YAM97, ZHA98, LAI00, GUO02, YAM03, AWA04, MILGA05] or by simultaneous acquisitions [KOLI92, MILL01, WYA03]. In off-axis configurations, U. Schnars [SCHN94b] has demonstrated the possibility of measuring specimen deformations by evaluating the phase difference between two states of the specimen. However, this double exposure technique does not give the absolute phase of the specimen. A solution for absolute phase measurements has been proposed by E. Cuche in off-axis geometry [CUC99a] and delivered patent [CUCPat]. A flat reference surface is taken on a flat part of the specimen and a procedure is performed to compensate for the phase deformation. The complete wavefront is thus reconstructed out of a single hologram, which retrieves the initial aim of holography. E. Cuche also showed [CUC99b] that the phase compensation technique could be applied in holographic microscopic methods. Later on other techniques were developed to perform the phase reconstruction out of a single hologram [LIE03, LIE04]. P. Ferraro [FERR03a] performs a method in which a reference hologram is recorded and then subtracted to the hologram of interest to compensate for the phase deformations. G. Indebetouw developed a method, called Spatiotemporal digital holograph, that avoids the need for high spatial bandwidth detectors and high spatial coherence, leading to speckle noise [IND99, IND01]. Nowadays, digital holographic microscopy has become a wide used method [ZHA98, TAK99, TIS01, XU01, YAM01, DUB02, CARL04, COP04].
Other developments include color digital holography [KAT02, YAM02, ALM04, JAV05b], polarization digital holography [LOH65, COLO02b, COLO04, COLO05], synthetic wavelength digital holography [ONO98, WAG00, GAS03], tomography [KIM99, KIM00, DAK03, MONT06], optical diffraction tomography [CHAR06a, CHAR06b] and several aberration compensation techniques [CUC99b, STA00, PED01b, DEN02, FERR03b, FERR03a, IND01, MAL05, YON05, COLO06a, COLO06b, COLO06c]. The development of DHM allows truly non-invasive examination of biological specimens and therefore it becomes an increasing powerful technique for biomedical applications [COLO02a, TIS05, MAS05, MAL05, MARQ05, JEO05, JAV05a, RAP05].