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The U.S. Laser offers a series of harmonic generators for converting near infrared light into visible or u. v. light by generating the second, third, or fourth harmonics. Designed primarily for use with U.S. Laser's fundamental (TEM00) mode acousto-optically q-switched Nd:YAG lasers. The systems are also applicable to other lasers operating similarly. If you are unsure as to the suitability of one of our products for your use, please contact our sales department for technical assistance.
Our harmonic generators generally fall into two main categories, angle tuned, also known as critical phase matching, and temperature tuned, also known as non critical phase matching. With angle tuning, the harmonic generator crystal is oriented and cut at a specific angle, and is fine tuned by tilting the crystal to achieve optimum phase matching. U.S. Laser's angle tuned systems are provided with a precision five axis mount, to provide the alignment control required. With temperature tuning, the crystal is mounted in a specially designed oven, and the temperature is elevated to the optimum phase match temperature. Once the optimum temperature is achieved, a precision temperature controller regulates the temperature.
For the second and third harmonic, the harmonic
generator crystals are placed inside of the laser resonator
cavity (intracavity) . This orientation is done to improve conversion
efficiency, since the intracavity circulating power is significantly
higher than the power coupled out of the cavity. When generating the
second harmonic intracavity, a special front laser cavity
mirror (PN3415) is provided with the SGH assembly. This mirror
fully reflects the fundamental wavelength while transmitting the second
harmonic. The mirror effectively acts as a beam separator, and the
laser output will be exclusively the second harmonic, with no residual
fundamental radiation. In third and fourth harmonic generation, the
output is a mixture of the fundamental and the harmonic, and requires
the beams to be separated. To accomplish this, USL offers a dichroic
beam separator assembly which transmits the harmonic wavelength while
rejecting the unwanted wavelength. Unlike a beam separating prism, the
beam separator does not deviate the beam path.
GENERATORS: Second harmonic generators are used to
convert the fundamental Nd:YAG wavelength of 1064 nm to the second
harmonic at 532 nm. The SHG assembly is designed primarily for use
intracavity with acousto-optically q-switched lasers operating in
fundamental mode. Three SHG doubler assemblies are offered, two angle
tuned, and one temperature tuned.
MIRROR INLINE CAVITY
: Conventional frequency doubler
systems (such as the model 1007-1 thru -3) efficiently transmit 532 nm
radiation that is generated in the forward direction thru the SHG
crystal. Unconverted 1064nm radiation reflected from the front mirror
returns thru the SHG crystal in the rearward direction, and is also
converted to 532 nm. This energy may be reclaimed by using a third
mirror in the cavity which reflects the rearward 532 nm radiation back
to the laser output. Using this concept it is possible to extract as
much as 25%-40% more 532 nm radiation than is possible with a
conventional two mirror cavity system.
HARMONIC GENERATOR: The third harmonic of Nd:YAG at 355 nm
is generated by sum-frequency mixing of the fundamental 1064 nm
radiation with the second harmonic 532 nm. Two crystals are placed
intracavity, both the second harmonic crystal, and the third harmonic
crystal. The laser output is a mixture of the second harmonic at 532
nm, and the third harmonic at 355nm, and therefore, a beam separator
must be used.
HARMONIC GENERATOR: The fourth harmonic generator is used
extracavity to convert the second harmonic output at 532 nm to the
fourth harmonic at 266 nm. The output is a mixture of 532nm and 266 nm
light, and therefore, a beam separator is required.
HARMONIC GENERATOR CELLS: Replacement cells provide an easy
way to change or replace a damaged harmonic generator crystal. Handling
and mounting crystals requires extreme care and cleanliness. USL takes
the worry out of the job by providing complete cells with premounted
crystals. Cells are directly compatible with corresponding USL angle
tuned or temperature tuned mounts.
SEPARATOR ASSEMBLY: When generating the third and fourth
harmonics of Nd:YAG, the harmonic generator output is a mixture of the
two wavelengths. For the harmonic wavelength to be usable, it must be
separated. A dispersion prism may be used, but the two beams are
deviated at different angles to the normal beam path. To be useful, the
beam must now be redirected back to the normal beam path. The USL beam
separator design uses a series of four dichroic mirrors. As the beam
travels thru the separator, the harmonic beam is fully reflected while
>99% of the unwanted wavelength is transmitted and absorbed.
Using this scheme the unwanted wavelength is attenuated by a factor of
approximately 108. To allow for correction of
any small walk off that may occur as the beam travels thru the
separator, the last dichroic mirror is mounted in a kinematically