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US LASER CORP: Product Catalog

Harmonic Generation

TABLE OF CONTENTS

Harmonic Generator Assemblies

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.

SECOND HARMONIC 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.

N1007-1 An angle tuned SHG assembly consisting of a 3mm x 3mm x 5mm long Type II, dual band A/R coated KTP crystal mounted in a cell. A precision 5 axis mount is provided for phase match tuning. Maximum recommended beam diameter is 2mm. This system is designed primarily for use with lasers operating in fundamental (TEM00) mode, but, because of KTP's large angular acceptance, may also be used with low order multimode lasers with beam diameters 2mm or less. Assembly includes cell mounted crystal, 5 axis mount, and dichroic front laser cavity mirror.
N1007-1-1 Same as P/N 1007-1 above, but with a 3mm x 3mm x 3mm KTP crystal designed for use with lower powered lasers.

Model N1007-1 SHG Assy with 5 Axis Angle Tuned Mount

N1007-2 An angle tuned SHG assembly consisting of a 3mm x 3mm 15mm long Type II dual band A/R coated LBO crystal mounted in a cell. A precision 5 axis mount is provided for phase match tuning. Also included is a specially coated dichroic front laser cavity mirror. This crystal has a higher damage level than KTP, but has lower conversion efficiency. Maximum recommended beam diameter is 2mm. This system is designed primarily for use with higher powered lasers operating in fundamental (TEM00) mode.

Note: Because all SHG crystals have a small amount of light absorption, angle tuned crystals may suffer some power drift as the crystal heats up. For maximum stability, USL recommends use of a temperature stabilization loop consisting of a crystal heater and temperature regulator. To add this option to the above angle tuned SHG assemblies, add -TS to the end of the part number.

N1007-3 A temperature tuned SHG assembly consisting of a 3mm x 3mm x 20mm long Type I, dual band A/R coated LBO crystal mounted in a cell and housed in an oven. The oven is heated and temperature regulated by a precision controller which is included. Also included is a specially coated dichroic front laser cavity mirror. Because the SHG crystal must reach phase match temperature prior to operation, this system requires approximately 5 minutes warm up time. Temperature tuned SHG assemblies include special cell mounted crystal, crystal oven and temperature controller, 5 axis adjustable mount, and dichroic front laser cavity mirror.

Model N1007-3 Temperature Tuned SHG Assembly with crystal oven, temperature controller, and adjustable mount

THREE 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.

N1007-6 The three mirror cavity accessory consists of a specially coated low loss mirror which is coated to reflect the 532 nm light while fully transmitting the 1064 nm fundamental radiation. The mirror is mounted in a specially designed kinematically adjustable mirror mount to allow for coincidence adjustment of the two 532 nm beams.

3 Mirror Cavity with Kinematically adjustable Mount

THIRD 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.

N1007-4 A third harmonic generator assembly consisting of an angle tuned 3mm x 3mm x 10mm long dual band A/R coated Type I LBO crystal mounted in a cell. A precision 5 axis mount is provided for phase match tuning. Also included is a specially coated dichroic front laser cavity mirror (P/N 3416), which totally reflects the 1064 nm, while transmitting 532 nm and 355 nm light. For stability, the crystal cell is mounted in a heater, and a temperature controller is provided to regulate the crystal temperature. A dichroic beam separator is provided (P/N 1015-2) to transmit the 355 nm radiation while rejecting the 532 output. This package does not include the pre-requisite second harmonic generator.

FOURTH 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.

N1007-5 A fourth harmonic generator assembly consisting of an angle tuned 4mm x 4mm x 7mm long dual band A/R coated Type I BBO crystal mounted in a sealed cell. A precision 5 axis mount is provided for phase match tuning. A dichroic beam separator is provided (P/N N1015-3) to transmit the 266 nm radiation while rejecting the 532 output. This package does not include the pre-requisite second harmonic generator.

REPLACEMENT 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.

N1007-7 Replacement frequency doubler cells.
N1007-7-1 3mm x 3mm x 3mm dual band A/R coated KTP crystal mounted in standard cell.
N1007-7-1A Same as above, but mounted in temperature stabilized cell.
N1007-7-2 3mm x 3mm x 5mm dual band A/R coated KTP crystal mounted in standard cell.
N1007-7-2-A Same as above, but mounted in temperature stabilized cell.
N1007-7-3 3mm x 3mm x 15mm dual band A/R coated angle tuned LBO crystal mounted in standard cell.
N1007-7-3-A Same as above, but mounted in temperature stabilized cell.
N1007-7-4 3mm x 3mm x 20mm dual band A/R coated, temperature tuned LBO crystal mounted in crystal oven cell.
N1007-8 Replacement frequency tripler cells.
N1007-8-1 3mm x 3mm x 10mm dual band A/R coated angle tuned LBO crystal mounted in temperature stabilized cell.
N1007-9 Replacement frequency quadrupler cells.
N1007-9-1 4mm x 4mm x 7mm A/R coated angle tuned BBO crystal mounted in standard cell.

Standard Angle Tuned Harmonic Generator Cells

Temperature Tuned / Temperature Stabilized Cell

BEAM 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 adjustable mount.

N1015-1 Fourth harmonic beam separator, separates 266nm from 532 nm
N1015-2 Third harmonic beam separator, separates 355 nm from 532 nm
N1015-3 Second harmonic beam separator for use with extracavity harmonic generators. Separates 532 nm from 1064 nm.

Beam Separator Assembly (cover removed)

 


 

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This page was last modified on: 6/18/2012