Cavity Structure/Spacer: Diameter 10 mm to 100 mm (typical)

Q: Why is thermal expansion coefficient critical for cavity spacers?

A low thermal expansion coefficient (e.g., <1e-7/K) minimizes cavity length changes with temperature, ensuring stable resonant frequencies and laser wavelength, which is crucial for applications like metrology and spectroscopy.

Q: How does spacer parallelism affect laser performance?

Poor parallelism causes misalignment between mirrors, leading to higher diffraction losses, reduced finesse, mode distortion, and potential lasing threshold increase or unstable output.

Component Specifications

Definition

A critical mechanical component in optical resonators that precisely separates and aligns reflective surfaces (mirrors) to define the resonant cavity length. It ensures dimensional stability against thermal expansion, mechanical stress, and environmental factors, directly influencing the resonator's optical path length, mode structure, and laser output characteristics such as wavelength stability and beam quality.

Working Principle

The spacer maintains a fixed physical distance between resonator mirrors, establishing the optical cavity length (L). This length determines the resonant frequencies (longitudinal modes) via the condition L = m(λ/2), where m is an integer and λ is the wavelength. It mechanically constrains the mirrors to ensure parallel alignment, minimizing diffraction losses and mode distortion. Thermal management principles are often integrated to counteract length variations from temperature changes.

Materials

Typically ultra-low expansion (ULE) materials: fused silica, Zerodur, or Cervit for thermal stability; invar or super-invar for metallic options; sometimes silicon carbide or carbon composite for high stiffness-to-weight ratios. May include thermally conductive elements like copper for active temperature control.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Length	10 mm to 500 mm (cavity-dependent)
Diameter	10 mm to 100 mm (typical)
Parallelism	< 1 arcsecond
Length Tolerance	±0.1 μm to ±1 μm
Surface Flatness	λ/10 to λ/20 at 633 nm
Thermal Expansion Coefficient	< 1 × 10⁻⁷ /K

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 10110, ISO 14999, DIN 3140

Parent Products

This component is used in the following industrial products

Optical Resonator

A cavity structure that confines and amplifies light through multiple reflections to sustain laser oscillation.

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Engineering Analysis

Risks & Mitigation

Thermal drift altering cavity length
Mechanical creep over time
Vibration-induced misalignment
Material outgassing in vacuum systems

FMEA Triads

Trigger: Temperature fluctuations
Failure: Cavity length change, wavelength drift
Mitigation: Use ULE materials; implement active temperature stabilization with Peltier elements or ovens.

Trigger: Mechanical stress from mounting
Failure: Bending, loss of parallelism
Mitigation: Design symmetric mounting; use stress-relieved materials; apply finite element analysis (FEA) for load distribution.

Trigger: Vibration from environment or equipment
Failure: Mirror misalignment, phase noise
Mitigation: Employ vibration isolation platforms; design rigid, high-stiffness spacer geometries; use damping materials.

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Length tolerance per ISO 10110-5; surface specifications per ISO 14999

Test Method

Interferometric measurement (e.g., Fizeau interferometer) for length and flatness; autocollimator for parallelism; thermal cycling tests for expansion coefficient verification.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Frequently Asked Questions

Why is thermal expansion coefficient critical for cavity spacers?