NOVELTY - Isotope separation comprises exciting molecules by laser pulses (1, L1-L2), extracting excited molecules out of gas (2) so that the molecules are existent in a composition determined by the form of the laser pulse (L5-L7), and shaping the pulse(s) in an iterative process by varying the form of the laser pulses as function of the composition of the extracted molecules after their absorption of energy quanta.    USE - Used for separating molecules with different excitation spectra.    ADVANTAGE - The process functions only if the quantum states of the isotopes as well as the time span where the oscillating wave packets diverge are precisely calculated. It does not requires exact calculations regarding the excitation energy and pulse lengths or the pauses between laser pulses to achieve the intended separation of the molecules. It has short interaction period of the laser pulse down to the sub-Pico second range allowing a fast separation of molecules relative to the hampering internal energy redistribution to other vibrational modes. It requires long time duration for isotopes separation.    DETAILED DESCRIPTION - Isotope separation comprises exciting molecules by laser pulses so that the molecules to be separated are transferred into a state of excitation due to multi-absorption of energy quanta of laser pulses, extracting the excited molecules out of gas so that the molecules are existent in a composition determined by the form of the laser pulse, and shaping the pulse(s) in an iterative process by varying the form of the laser pulses as function of the composition of the extracted molecules after their absorption of energy quanta. The molecules are part of gas.    INDEPENDENT CLAIMS are included for the following:    (1) a molecules separating device comprising laser to excite the molecules by laser pulses, a pulse modulator (4) to shape the pulse of the laser, a device to extract multi-excited molecules from the gas, a detector to detect the extracted molecules, and a control unit controlling the pulse modulator in an iterative process so that the form of the laser pulses is varied until the molecules detected by the detector are showing composition optimizing according to the composition; and    (2) a computer program for adjusting the laser pulses of a laser comprising an evaluation mechanism for evaluating the measured composition of molecules with different excitation spectra, and extracted from the gas; and a comparative mechanism for automatic comparison of the measured composition with composition. The control mechanism depending on the result of the comparison automatically initiates in a further iteration a variation of the form of the laser pulses or the form of the laser pulses remains unchanged.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of isotope separation.    Laser pulses (1)    Laser pulses (1, L1-L2)    Gas (2)    Ion detector (3)    Modulator (4)    Form of the laser pulse (L5-L7)