Large-Aperture LBO Crystals: Selection and RFQ Checklist

A request for a “large-aperture LBO crystal” still leaves several questions open. Does the dimension refer to the outside of the crystal or the usable optical area? Is the part for frequency doubling or a later conversion stage? Will it operate in an oven?

Those details affect whether two quotations describe the same component. This guide focuses on what to put on the drawing and in the enquiry before comparing price or delivery time.

Start with the conversion stage, not the crystal size

Lithium triborate, LiB₃O₅, is a nonlinear optical material used for frequency conversion. For a 1064 nm laser, common LBO configurations include second-harmonic generation to 532 nm and sum-frequency mixing of 1064 nm with 532 nm to produce 355 nm. These are different optical tasks and do not use an interchangeable specification.

State the wavelengths entering and leaving the proposed crystal, their polarizations and the intended operating temperature. If the target is 266 nm, provide the complete conversion scheme rather than assuming that an LBO part specified for 355 nm will also suit that stage.

Published EKSMA nonlinear-crystal configurations illustrate how LBO cut angles, coatings and temperature requirements differ between conversion arrangements. Catalogue examples are useful references, but they are not a substitute for checking your optical design.

Separate external dimensions from clear aperture

Write the crystal dimensions as width × height × length, and identify the direction of beam propagation. Then specify the minimum clear aperture separately. The external face size alone does not define the area over which the required optical quality is guaranteed.

Include the beam diameter at the crystal and its definition, such as a 1/e² intensity diameter. If the beam is elliptical, give both axes. The usable aperture needs to accommodate the beam and the alignment allowance of the actual system; there is no single margin that can be applied to every layout.

For a larger custom part, ask which inspection requirements apply across the clear aperture. A wavefront measurement over a small central region is not the same acceptance condition as a measurement across the full usable face.

“Large aperture” is a relative description, not an orderable size. Put the required dimensions and optical area on the drawing, and ask the supplier to confirm feasibility rather than infer it from the phrase.

Confirm the cut and the temperature arrangement together

LBO can be used in angle-tuned or temperature-tuned configurations. A temperature-tuned, non-critical phase-matching arrangement is not simply a standard room-temperature part placed in a heater. Its cut, wavelength combination and operating temperature need to be specified together.

When an oven is part of the design, include the available mounting space and ask how the crystal will be held. EKSMA’s crystal ovens and holders show examples of temperature-stabilized mounting arrangements; their published capabilities should not be assumed for an unspecified holder.

If replacing an existing crystal, send the original drawing, cut information and coating description. If a supplier proposes different angles, dimensions or a different thermal arrangement, request the alternative as a separate option. It should not be hidden inside an otherwise similar quotation.

Do not use a bulk damage threshold as a coated-part guarantee

A laser-induced damage threshold needs test conditions to be meaningful. Wavelength, pulse duration, beam size, repetition rate and beam profile all matter. A figure without that context is not enough to establish whether a component is suitable for your laser. Edmund Optics explains the information needed to interpret an LIDT specification.

State whether your source is CW or pulsed. For pulsed operation, provide both pulse energy and average power where available, together with pulse duration and repetition rate. Do not describe the operating condition only as “high power.”

Ask whether quoted damage data refer to the crystal bulk, a polished surface, a coating sample or a representative finished component. These should not be treated as the same test. A reference value also should not be presented as a promise that every delivered part has undergone destructive damage testing.

Specify each optical face

“AR coated” is incomplete. Identify the wavelengths required on each face, the angle of incidence, polarization and the acceptable residual reflectance. Label the faces on the drawing so that the coating schedule cannot be read in two different ways.

The choice between coated and uncoated surfaces belongs in the optical design. Newlight’s LBO product information describes both coating options and uncoated Brewster-cut configurations. Neither should be selected solely because it appears to offer the highest damage-threshold number.

For the acceptance specification, distinguish surface flatness from transmitted wavefront distortion. If an interferometric requirement is given as a fraction of a wavelength, include the test wavelength and the measurement aperture. Also identify the required surface-quality convention rather than using “optical grade” as the only description.

A concise LBO enquiry checklist

Compare the scope of supply before the price

For a custom LBO enquiry, ask the supplier to separate the crystal specification from the mounting, coating and inspection scope. A lower price is not a like-for-like comparison if one offer excludes the holder or an agreed test report.

Request a written list of deviations and confirmation of delivery time after the drawing is reviewed. Do not assume that a catalogue crystal establishes availability for a larger aperture, a different length or a custom coating.

To discuss an LBO requirement with ATR Crystal, send the drawing and operating conditions through our enquiry page. Availability, achievable specifications and inspection options should be confirmed for the individual request. For background on the gain materials used in solid-state laser systems, see our laser crystal selection guide; gain-medium selection and nonlinear frequency conversion are separate parts of the design.