An adjustable repetition rate laser engine comprising: an oscillator that generates and outputs a beam of femtosecond seed pulses; a stretcher that stretches a duration of the seed pulses; and an amplifier that; receives the stretched seed pulses from the stretcher, amplifies an amplitude of selected stretched seed pulses to create amplified stretched pulses, and outputs a laser beam of amplified stretched pulses; wherein the amplifier comprises a dispersion compensator that reduces a dispersion of the amplified stretched pulses; a compressor to compress a duration of the amplified stretched pulses; said stretcher and said compressor are an integrated stretcher-compressor, comprising a chirped volume Bragg grating (CVBG) adapted to; receive the seed pulses at one end; stretch a duration of the seed pulses by introducing different delay times for the "red", "green" and "blue" components of such "white" seed pulses, producing stretched seed pulses, "blue" and "red" referring to the portions of the infrared spectrum which have shorter and longer wavelengths within the bandwidth of the pulse; receive the laser beam of amplified stretched pulses at its opposite end; compress a duration of the amplified stretched pulses by delaying its "red" components relative to its "blue" components, or vice versa, to the same degree as they were delayed during the stretching step; and output a laser beam of amplified compressed femtosecond pulses with a pulse duration of less than 1,000 femtoseconds; and said amplifier comprises; an optical cavity that is coupled to the stretcher-compressor to receive and circulate the stretched seed pulses in a number of roundtrips, an optical switch device (330,340) coupled to the optical cavity to control coupling of the light of the received stretched seed pulses into the optical cavity and to control coupling of light inside the optical cavity out as amplified stretched pulses, wherein the optical switch device is configured to control and adjust the number of roundtrips of the light coupled inside the optical cavity to control and adjust a pulse repetition rate of the amplified stretched pulses produced by the amplifier, an optical gain medium inside the optical cavity to amplify the stretched seed pulses into amplified stretched pulses, and a dispersion compensator inside the optical cavity to compensate a dispersion of the amplified stretched pulses introduced by optical elements (310,321-324, 330,340) of the amplifier within one roundtrip of light inside the optical cavity of the amplifier, excluding the dispersion caused by the dispersion compensator, wherein said introduced dispersion is quantified as a group delay dispersion; GDD = λ 3 d 2 η λ c 2 d λ 2 L where λ is the wavelength of the light, c is the speed of light, η(λ) is the wavelength dependent index of refraction and L is the length of the optical pathway in the optical cavity, and wherein the GDD of the optical elements (310,321-324, 330,340) present in the amplifier can be determined by measurement or inferred from the design, such that the dispersion compensator is structured to introduce a dispersion with a GDD of approximately equal and opposite value to the determined GDD of the optical elements present in the amplifier within the range of 5,000 fs 2 to 20,000 fs 2; and wherein the laser engine is adapted to output the laser beam with a repetition rate within the range of 50 kHz-1 MHz; and wherein the laser engine is adapted to output the laser beam with an output power greater than 0.1 W. an oscillator that generates and outputs a beam of femtosecond seed pulses; a stretcher that stretches a duration of the seed pulses; and an amplifier that; receives the stretched seed pulses from the stretcher, amplifies an amplitude of selected stretched seed pulses to create amplified stretched pulses, and outputs a laser beam of amplified stretched pulses; receives the stretched seed pulses from the stretcher, amplifies an amplitude of selected stretched seed pulses to create amplified stretched pulses, and outputs a laser beam of amplified stretched pulses; receive the seed pulses at one end; stretch a duration of the seed pulses by introducing different delay times for the "red", "green" and "blue" components of such "white" seed pulses, producing stretched seed pulses, "blue" and "red" referring to the portions of the infrared spectrum which have shorter and longer wavelengths within the bandwidth of the pulse; receive the laser beam of amplified stretched pulses at its opposite end; compress a duration of the amplified stretched pulses by delaying its "red" components relative to its "blue" components, or vice versa, to the same degree as they were delayed during the stretching step; and output a laser beam of amplified compressed femtosecond pulses with a pulse duration of less than 1,000 femtoseconds;