SATURABLE ABSORBER FOR LASER SYSTEM

Abstract: Optical cell containing one or more organic dyes dissolved in a solid substance, preferable catalyzing glue, inserted between two plates, (1) and (2), of suitable material, transparent to laser light. Such cell may find application within a laser cavity, as an optical device with saturable absorption, to obtain a "Q switch" and/or "mode locking". Such cell may furthermore be used as an active source, i.e. as a laser, light emitter in a resonant cavity, either optically primed by a lamp, by an other laser or by other means.

Description: . Saturable absorber for laser system. The invention is concerned with an optical cell containing one or more organic dyes (such as BDN-14 DIS-KODAK) dissolved in a solid substance, preferably catalyzing glue ' (such as HARTEL INTERPRISES 17024 B) set between two plates, (1) and (2), of suitably transparent material. This invention belonges to the field of optical systems, and, more precisely, to pulsed and continuous laser optics. There are already in existance solutions adopting saturable obsobers for solid state pulsed Nd YAG and Nd Glass lasers, but here the dissolved organic dye (Polymethilmelacrylate) which operates as a saturable obsorber (by saturable we mean that below a given laser intensity threshold the cell is not transparent, while above this threshold the cell becomes transparent to the laser radiation), functions as a passive "Q 2 switch" with damaging thresholds lower or equal to 200 M /cm and are of mediocre optical quality in terms of homogeneity. These two inconveniences pose limitations to their application to high power lasers and to lasers from which high quality output beam optics is required. The purpose of the present invention is to eliminate the inconveniences mentioned above. The invention, as o Gt* characterized by the claims to follow, solves the problem of . 2 obtaining a higher damaging threshold: 250 M /cm ; it makes possible applications to lasers working also at average repetition frequency, such as 10 pps (pulses per second); it provides better optical quality: a duration which exceeds 3 x 5 . 10 pps (a threefold improvement over previous solutions). The present invention therefore takes regard for a composite containing organic dyes, dissolved ' in a solid substance, to be used as saturable absorbers for mode locking or active source devices. The invention will now be described with reference to one of its preferred forms and is reported as an illustration and is not limited to this, referred to the figures attached: Figure 1 shows a schematic of the optical cell, where: (1) and (2) are the plates of suitable transparent material (glass, plastic, saffire etc.); (3) is a solid substance, preferably • optically and/or chemically catalyzing glue into which a suitable molar concentration of the organic dye adopted is dissolved. S , S , S , S show the surfaces which have been optically - < ---> ~~r treated with possible antireflecting coating. The organic dye may be dissolved in the glue in the fluid state using a suitable solvent, such as acetone, then the resulting composite is filtered with porous membranes and centrifυged to eliminate the undissolved parts of the organic dye. The fluid resulting may be again mixed with a further addition of glue without any dye to obtain the desired molar concentration. The composite obtained, when chemical catalyzing glues are used, greed of the solvent used, is placed under a vacuum bell at suitable temperature (such as 50°). The resulting composite is mixed with the catalyzer and again placed in a vacuum, in the conditions described above, to remove possible air bubbles. The composite (3) is then inserted between the two plates (1) and (2) so as to build the optical cell. The plates, before the glue sets, are optically designed by means of an optical interferometer. The optical cell obtained may find a number of applications: 1. Q switch 2. Mode lock 3. Active source 1. When inserted into a laser cavity, the cell can give way to stimulated emission of coherent pulses having a duration of 1 to 30 ns with the same characteristics of a Q switch; 2. In the mode lock case, the pulse is made up of a train of pulses ranging between 10 and 100 ns, each one lasting from 1 to 100 ps. This behaviour is solely due to the optical proprieties of the saturable obsorber and to the characteristics of the active means (Nd YAG, GLASS etc.) used as well as the optical priming mode. 3. As an active source, the cell, suitably primed through a flash lamp or an other laser, is itself a light source and is therefore active material of the laser cavity into which it is inserted. This optical cell, as described, has the following advantages: - different types of application; - structure simplicity: - availability of its components on the free market - very long average life compared to previous solutions (greater reliability) - no need for maintenance. It is worth noting that by varying the thickness of the composite between the plates the optical density can be controlled. This permits to use such cell in a wide range of laser configurations and at a large range of priming energy levels.

Claims: CLAIMS 1. Optical cell functioning as a saturable absorber, characterized by being made up of an organic dye, such as BDN type 14015, produced by Kodak, dissolved in a solid substance, such as catalyzing glue. 2. Optical cell, as per claim 1, characterized by the fact that it may be used within a laser cavity with passive Q switch functions. 3. Optical cell, as per claim 1, characterized by the fact that it may be used outside a laser cavity, with saturable attenuator functions. 4. Optical cell, as per claim 1, characterized by the fact that it may be used within a laser cavity in a mode lock role. 5. Optical cell, as per claims 1, 2 or 3 or 4, characterized by the fact that by varying the thickness of composite (3) between surfaces S , S , S , S , such cell may be adapted 1 2 3 4 to "' a number of laser configurations and to different priming energy levels. 6. Optical cell as shown in the description above and in the drawing attached, as also in any part thereof in isolation or in combination.

Inventors: BIANCHI ALFREDO, GIULIANI GIAMPIERO, LANDONI ANTONIO, BIANCHI, ALFREDO, GIULIANI, GIAMPIERO, LANDONI, ANTONIO
Applicants: SELENIA IND ELETTRONICHE, SELENIA, INDUSTRIE ELETTRONICHE ASSOCIATE
Application year: 1985
Main classification: H01S3
IPC codes: H01S3