Coherent light generators – Particular beam control device – Nonlinear device
Reexamination Certificate
1999-01-12
2001-11-20
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Particular beam control device
Nonlinear device
C372S020000, C372S031000, C372S100000, C372S102000, C372S092000, C359S330000
Reexamination Certificate
active
06320886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser device.
2. Discussion of Prior Art
Optical parametric generator's (OPG's) have been used to generate laser-like output within a certain spectral range. The OPG comprises a non-linear crystal material to which a pump source is applied. The spectral range is constrained by the pump source wavelength, the type of non-linear material used and the relevant geometry-type implemented. The output of an OPG is usually of relatively narrow spectral bandwidth, centred at a wavelength determined by the angle of the crystal axis relative to the pump to axis. Conventionally, the centre wavelength can be continuously tuned by altering the orientation or changing the temperature of the crystal, tuning taking place through consideration of the principle of conservation of momentum, namely phase matching in the terminology of non-linear optics. Normally, for a certain orientation of the crystal, only a narrow spectral range of signal and idler wavelengths satisfy the phasematch constraints, thus only a narrow spectral range of signal and idler wavelengths can be generated simultaneously. Attempts have been made to obtain broader spectral bandwidth output using dye or vibronic laser systems, but the dyes used in dye systems may be harmful and special safety precautions are required, while vibronic systems are complex to operate and the bandwidths obtained are small, typically less than 50 nm.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, a laser device comprises a non-collinear optical parametric generator (OPG); and a pump wave source; the OPG comprising a non-linear crystal fixedly mounted within the generator; wherein the relative orientations of the pump wave and each generated wave to an optic axis of the non-linear crystal are substantially such that a point of in flexion is produced in a tuning curve of wavelength versus pump wave orientation of one of the generated waves, whereby a broadband spectral output is obtained.
The present invention produces a broadband output from a device which is robust and safer and simpler to use than conventional broadband devices, as well as giving a greater bandwidth.
Preferably, the device further comprises reflecting means for forming a resonator in which at least one of the generated waves is resonant. The pump wave may enter the OPG directly or through the reflecting means, but preferably, the laser device further comprises a pair of reflectors, whereby the pump wave is coupled to the OPG.
Preferably, the reflectors comprise a pair of dichroic mirrors.
Preferably, the device further comprises pump wave reflecting means, whereby the intensity of the pump wave source is enhanced.
In accordance with a second aspect of the present invention, an amplifier comprises a device according to the first aspect and means for injecting a seed wave into the device.
In a conventional narrowband OPG amplifier, the crystal within the OPG has to be rotated to match the wavelength of the seed wave, but in the present invention this is not required, leading to a simpler construction. The invention also enables a broader gain bandwidth and enhanced spectral coverage to be achieved for broadband amplification.
In accordance with a third aspect of the present invention, a continuously tuneable narrowband source comprising a laser device according to the first aspect of the invention, further comprises reflecting means; wherein the reflecting means comprise at least one mirror and tuning means; and wherein the at least one mirror is fixed and the tuning means are movably mounted, such that a continuously tuneable narrowband output is produced.
Conventionally, the crystal would need to be reoriented each time the source is tuned, whereas the present invention only requires the tuning means to be adjusted.
The tuning means may comprise an etalon, but preferably, the tuning means are dispersive. Any suitable component which has dispersive properties may be used, but preferably, the dispersive tuning means comprise a Littrow or Littman mounted grating, a Littrow prism or an acousto-optic deflector.
In accordance with a fourth aspect of the present invention, a coherence tomography source comprises a laser device according to the first aspect of the invention.
The increased bandwidth of the device of the present invention, gives a shorter coherence length permitting 3-D imaging with enhanced resolution.
In accordance with a fifth aspect of the invention, a system for spectral analysis of a medium comprises a laser device according to the first aspect of the invention; the system further comprising analysing means; wherein one of the generated waves comes into contact with a medium; and the analysing means analyse the spectrum of the generated wave after contact.
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Dawber William
Dunn Malcolm H
Rae Cameron F
Wang Jian
Jr. Leon Scott
Nixon & Vanderhye P.C.
The Secretary of Defence in Her Britannic Majesty's Governm
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