The invention relates generally to lasers for producing very short pulses and more particularly to fiber lasers for producing subpicosecond pulses.
There is great interest in generating subpicosecond laser pulses, down to pulsewidths of 100 fs or less. There is a wide range of applications that can be performed using subpicosecond laser pulses, e.g. electro-optic (EO) sampling. However, it has been quite difficult and costly to produce such short pulses.
One present system for generating subpicosecond pulses uses a large expensive Argon ion laser to pump a complex dual dye jet dye laser. Commercial systems of this sort produce 500 fs pulses; specially engineered systems can reach 100 fs. In another system the output of a large water cooled Nd:YAG laser (e.g. Spectra-Physics Model 3400) is passed through a pulse compressor and the compressed pulses are used to pump a dye laser, producing 300 fs pulses of tunable wavelength. Thus, although systems are available which produce subpicosecond pulses, their main disadvantage is their high cost and complexity, which limit availability.
In one type of fiber laser a rare earth such as neodymium, erbium or terbium is doped into the core of an optical fiber to provide an active gain medium. Pumping radiation input into the fiber causes lasing action in the fiber. The fiber is included in the laser resonant cavity.
Another type of fiber laser is the fiber Raman laser, as described in the Handbook of Laser Science and Technology, Section 2: "Solid State Lasers", Subsection 2.4 "Fiber Raman Lasers", R. H. Stolen and C. Lin, pages 265-273. A mode locked Nd:YAG or Argon laser is used to synchronously pump a fiber, and the Raman effect in the fiber provides gain, in a fiber Raman oscillator. Pulse broadening usually occurs for short pump pulses as a result of dispersion in the fiber. However, a dispersion compensated fiber Raman oscillator, as described in U.S. Pat. No. 4,685,107 issued Aug. 4, 1987 to J. D. Kafka etal, can generate subpicosecond pulses. A fiber has also been used for pulse shaping in a complex laser system, as shown by "The soliton laser", L. F. Mollenauer and R. H. Stolen, Opt. Lett., Vol. 9, No. 1, Jan. 1984, pages 13-15.