Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
1997-11-19
2002-10-15
Davie, James W. (Department: 2881)
Coherent light generators
Particular resonant cavity
Specified cavity component
C359S584000, C372S018000, C372S025000
Reexamination Certificate
active
06466604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical component designed preferably for use in a laser configuration, for the generation of a pulsed laser beam, especially a pulsed beam in the micro- to femtosecond range, and for use in an optical layout for a pulsed laser.
2. Description of the Background Art
Short pulses in the micro- to femtosecond range can be generated via mode coupling, Q-switching, or mode-coupled Q-switching within a laser cavity. This can be accomplished using a saturable absorber positioned in the laser cavity. The saturable absorbers used are dyes or semiconductors whose absorption capacity decreases with increasing beam intensity. In this manner, a coupling of the different resonant cavity modes to the short pulses oscillating in the cavity occurs, as is graphically described in H. Weber/G. Herziger, Laser-Grundlagen und Anwendungen [Laser Principles and Applications], Physik Verlag GmbH, Weinheim/Bergstr., 1972, pp. 144 ff.
This made it possible to design saturable absorbers, for example, as so-called “antiresonant Fabry-Perot saturable absorbers,” as is described in U. Keller, “Revolution in the Generation of Ultra-Short Pulses,” TR Transfer No. 23, 1994, pp. 22-24. In these known-in-the-art saturable absorbers, a semiconductor absorber was used, which was integrated into a Fabry-Perot interferometer, approximately 400 &mgr;m thick, with a sandwich-type construction. This sandwich-type construction comprised, as with a Fabry-Perot (etalon), two reflector elements. The space between the two reflector elements was taken up by the saturable absorbing semiconductor material. The distance between the two reflective elements was such that the beam intensity inside the Fabry-Perot was always much lower than the incident intensity. In other words, the Fabry-Perot was operated in antiresonance. This sandwich-type construction is described in EP-A 0 609 015 (U.S. Pat. No. 5,345,454) and in EP-A 0 541 304 (U.S. Pat. No. 5,237,577), among other places.
A further sandwich-type construction for a saturable absorber is known in the art from L. R. Brovelli, et al., “Self-Starting Soliton Mode-Locked Ti-Sapphire Laser Using a Thin Saturable Absorber, Electronics Letters, Vol. 31, No. 4, 1995, pp. 287-288. In the “sandwich absorber” described here (see right column p. 287, second paragraph from the top), only one of the two Fabry-Perot reflectors is replaced by an antireflective film, that is, an antireflective coating; the saturable absorbing material is positioned in this case between the two cover elements of the sandwich.
SUMMARY OF THE INVENTION
With the optical component, which acts as and can be used as a saturable absorber in accordance with the invention, separate, individual, discrete optical elements, as have long been known in the art, are no longer assembled in a sandwich-type construction with the goal of minimization; instead, an “etalon-free” coating ensemble is created, in which each individual layer, together with the remainder of the ensemble, contributes to the overall phase-coupled behavior of the incident beam. The term etalon-free coating ensemble is understood to mean a coating which contains no locally quantifiable etalon. Only with this design formalism, and the resulting computational formalism, is it possible to position one or more layers having the saturable absorbing properties in this ensemble, allowing, of course, of the phase-coupled interrelations, such that an optimal, in this case saturable absorptive effect can be achieved.
In the invention, a coating is used, which no longer simply acts overall as an addition to the properties of the individual partial layers. The object is first and foremost to compose the overall coating ensemble. Only after this has been completed can the property of the ensemble be determined (mathematically, as with a filter calculation).
The invention uses a coating ensemble comprised of a multitude of layers, wherein only one removal or one modification of a single layer can change the entire nature of the coating. In contrast to the above-described sandwich construction, a matrix-type coupling of all the layers with one another is implemented here, such as is described, for example, in the theoretical observations of M. Born and E. Wolf, Principles of Optics, Pergamon Press, 1975, pp. 55-70. The modification of the physical data of a single layer (position in the ensemble, index of refraction, thickness of optical coating) will affect the properties of the overall coating.
Compared with the known-in-the-art sandwich-type construction, the optical component in the present invention can now be provided with the correct properties, via the proper calculation of the coating ensemble, to create an optimal resonator cavity. With the selection of the optical coating thicknesses and/or the coating material, and the positioning of these coatings in the ensemble, the properties of the ensemble can be set deliberately, as desired, and thus optimally adjusted. And more than just optical properties can be taken into consideration; for example, requirements regarding coating resistance, the precise frequency-based course of reflection, and especially, as is described in detail below, the optimal positioning of the absorber material, and thus its optimal impact, can be selected.
Because the construction of the coating ensemble produces a lower number of layers than the known-in-the-art sandwich-type construction, this coating can be produced more cost-effectively, using higher tolerances for the optical layer thicknesses to be used, and their indices of refraction. The outstanding “freedom of design,” which permits a multitude of possible combinations in the construction of and materials used in the layers, has proven to be particularly advantageous.
REFERENCES:
patent: 4860296 (1989-08-01), Chemia et al.
patent: 5265107 (1993-11-01), Delfyett, Jr.
patent: 5627854 (1997-05-01), Knox
patent: 0 541 304 (1993-05-01), None
patent: 0 609 015 (1994-08-01), None
patent: 073261382 (1996-09-01), None
patent: WO 85/03171 (1985-07-01), None
Brovelli et al, “Self-starting Soliton Mode-locked Ti-Sapphire Laser Using a Thin Semiconductor Saturable Absorber”, Electronics Letters, vol. 31, No. 4, pp. 287-289, Feb. 1995.*
“Revolution in the Generation of Ultra-Short Pulses,” U. Keller, TR Transfer No. 23, 1994, pp. 22-24. (No Month).
“Laser Principles and Applications,” H. Weber et al., Physik Verlag GMbH, Weinhein/Bergstr., 1972, pp. 144-157, (No Month).
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M. H. Ober, M. Hofer, U Keller and T. H. Chiu, “Self-starting diode-pumped femtosecond Nd fiber laser”, Optics Letters, vol. 18, Sep. 15, 1993.
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