Coherent light generators – Particular beam control device – Nonlinear device
Patent
1991-02-27
1992-12-22
Davie, James W.
Coherent light generators
Particular beam control device
Nonlinear device
372 41, 372 45, 372 75, H01S 310, H01S 3094
Patent
active
051739100
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a solid laser with an emission wavelength lying between 0.5 and 0.65 micrometers.
Such a laser is particularly suitable for use in isotopic separation processes.
2. Discussion of the Background
Processes for separating uranium isotopes by laser have been studied for several years. Their implementation requires the selective excitation of the uranium isotopes from laser sources, the frequency of which must be particularly well adjusted and controlled.
Among the methods which have been studied hitherto, there are those which use sources emitting at around 16 .mu.m and those which emit between 0.55 .mu.m and 0.65 .mu.m. This latter approach uses a copper vapour type of laser to pump a dye laser, the technology of which is quite critical.
The renewal of interest in solid lasers, particularly because of the possibilities offered by pumping with laser diodes (efficiency, compactness, lifetime, reliability, etc.) opens the way to new methods for separating uranium isotopes. Certain methods based on solid lasers have already been proposed.
However, these methods lead to bulky and expensive devices.
SUMMARY OF THE INVENTION
The invention therefore relates to a laser emitting at a wavelength lying between 0.55 .mu.m and 0.65 .mu.m and overcoming these disadvantages.
The invention therefore relates to a solid laser with an emission wavelength of 0.5-0.65 micrometers, characterised in that it comprises:
a laser rod based on chromium-doped Mg.sub.2 SiO.sub.4 placed in a resonant cavity;
at least one laser diode emitting towards the rod a pumping beam of wavelength lying between 0.75 and 0.8 micrometers;
a frequency doubler crystal receiving a beam emitted by the laser rod and emitting in exchange a beam of wavelength 0.5-0.65 micrometers.
BRIEF DESCRIPTION OF THE DRAWINGS
The various objectives and features of the invention will appear more clearly in the description which will follow, given by way of example in which reference is made to the appended figures, in which:
FIG. 1 represents a first example of an embodiment of the device according to the invention;
FIG. 2 represents a variant of an embodiment of the device of FIG. 1;
FIG. 3 represents a second example of an embodiment of the device according to the invention;
FIG. 4 represents another variant of an embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, provision is made for placing a rod of chromium-doped forsterite (Mg.sub.2 SiO.sub.4) in an optical cavity and for exciting it using a laser diode emitting at 0.8 .mu.m. This type of laser diode was designed especially for the present invention. It is produced from a ternary compound Ga.sub.1-x Al.sub.x As and its composition is such that
This material is the location of the laser emission by recombination of electron-hole pairs. It is built into a structure of the optical waveguide type by inserting an active layer of Ga.sub.1-x Al.sub.x As between two layers of Ga.sub.1-y Al.sub.y As of aluminium composition such that 0.2<y<0.4.
The wave generated by the laser rod 1 excited by the laser diode has a wavelength covering the spectrum lying between 1.1 and 1.3 .mu.m.
This wave emerging from the optical cavity is then doubled in frequency in a non-linear crystal.
The chromium-doped forsterite (Cr: Mg.sub.2 SiO.sub.4) laser has an emission spectrum at room temperature ranging from 1.167 .mu.m to 1.345 .mu.m with a peak in the emission centred on 1.221 .mu.m. Its absorption spectrum ranges from 0.4 to 1.1 .mu.m with a maximum located at around 0.75 .mu.m. Pumping it by a laser diode emitting at the wavelength of 0.8 .mu.m is therefore entirely appropriate.
In addition, a direct pumping by laser diodes operating at about 0.8 .mu.m enables a high-efficiency "solid state" source to be produced.
In fact, the lifetime of the fluorescence is of the order of 15 .mu.s, which is compatible with laser diodes. It is particularly suitable for pumping by laser diodes, especially when operat
REFERENCES:
patent: 4809291 (1989-02-01), Byer et al.
patent: 4932031 (1990-06-01), Alfano et al.
patent: 5025446 (1991-06-01), Kuizenga
Optics Communications, vol. 71, Nos. 3/4, May 15, 1989, Elsevier Science Publishers B.V., (NL) C. Zimmermann et al.: "Doubly-resonant second-harmonic generation in beta-barium-borate", pp. 229-234.
Applied Physics Letters, vol. 52, No. 26, Jun. 27, 1988, American Institute of Physics, D. C. Edelstein et al.: "Femtosecond ultraviolet pulse generation in beta-BaB.sub.2 O.sub.4 ", pp. 2211-2213.
Patent Abstracts of Japan, vol. 13, No. 285 (E-780) (3633) Jun. 29, 1989, & JP, A, 169086 (Seiko Espon Corp), Mar. 15, 1989.
Applied Optics, vol. 28, No. 9, May 1, 1989, V. Petricevic et al.: "Near infrared tunable operation of chromium doped forsterite laser", pp. 1609-1611.
Jano Patrice
Pocholle Jean-Paul
Puech Claude
"Thomson-CSF"
Davie James W.
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