Asphericon BAM25-175-B-632 Diffraction-Limited Beam Expander

Overview

The Asphericon BAM25-175-B-632 is a monolithic, diffraction-limited beam expander engineered for high-precision laser beam conditioning in demanding optical laboratory and industrial applications. Unlike conventional Keplerian or Galilean systems composed of multiple spherical elements, this expander employs a single aspheric mirror-based optical design—eliminating internal reflections, ghosting, and alignment sensitivity while preserving wavefront fidelity. Its core principle relies on aberration-corrected aspheric surface geometry to achieve near-theoretical diffraction-limited performance (Strehl ratio > 0.8) across the full 632 nm design wavelength. Manufactured in Germany using ultra-low-expansion glass substrates and CNC-polished to sub-500 nm RMSi surface irregularity, the BAM25-175-B-632 delivers exceptional beam collimation stability, minimal pointing error (< 5 µrad), and negligible focus shift over temperature gradients (±0.005 mm/°C). It is optimized for HeNe lasers and other continuous-wave sources operating at 632 nm, with broadband anti-reflection coating (Type B) ensuring low residual reflectance across 600–1050 nm—critical for multi-wavelength compatibility and harmonic generation setups.

Key Features

• Monolithic aspheric mirror architecture—no air gaps, no cemented interfaces, no alignment drift
• Diffraction-limited performance certified per ISO 10110-5; each unit supplied with individual interferometric test report and Asphericon factory calibration certificate
• Expansion ratio of 1.75× with input aperture of 12.4 mm and output aperture of 22.5 mm—engineered for optimal M² preservation and beam parameter product (BPP) stability
• M28×0.75 metric thread enables secure, repeatable integration into standard optomechanical mounts and kinematic platforms
• Laser damage threshold of 12 J/cm² (100 Hz, 6 ns, 532 nm) verified per ISO 21254-1—suitable for moderate-pulse-energy Q-switched and CW applications
• RoHS-compliant construction with traceable material certification (S-LAH64 substrate, certified optical-grade coating deposition)
• Thermal stability optimized for ambient operation (−10 °C to +50 °C); coefficient of thermal expansion matched between substrate and coating stack

Sample Compatibility & Compliance

The BAM25-175-B-632 is compatible with TEM₀₀ and low-order multimode beams up to 12 mm clear aperture input. Its aspheric surface profile is specifically calculated for 632 nm, minimizing spherical and coma aberrations under nominal incidence angles (0° ± 0.5°). The unit complies with ISO 9001:2015 manufacturing protocols and undergoes 100% post-production interferometric verification using Zygo Verifire™ HD interferometers. All coatings meet ISO 13665 spectral reflectance specifications and are tested per MIL-C-48497A for adhesion and environmental durability. Asphericon’s quality documentation supports GLP/GMP-aligned optical system validation, including full traceability of metrology equipment (NIST-traceable calibration certificates), batch-specific surface figure maps (Zernike coefficients up to 37th order), and environmental stress screening records (thermal cycling, vibration, humidity exposure).

Software & Data Management

While the BAM25-175-B-632 is a passive optical component, Asphericon provides comprehensive digital support for system integration and validation. Zemax OpticStudio (.zmx), CODE V (.seq), and OSLO (.len) files are available for download from the Asphericon Optical Design Library—enabling accurate modeling of beam propagation, M² degradation analysis, and tolerance stacking simulations. Each delivered unit includes a unique serial-numbered PDF certificate containing measured wavefront error (WFE) maps, PV and RMS surface deviation data, and spot diagram analysis at 632 nm. For customers implementing automated optical assembly lines, Asphericon offers CSV-formatted metrology exports compatible with LabVIEW, Python (NumPy/Pandas), and MATLAB workflows—supporting statistical process control (SPC) and Six Sigma compliance reporting.

Applications

• Precision interferometry and holography requiring stable, low-aberration reference beams
• Confocal microscopy illumination paths where beam uniformity and focus stability directly impact axial resolution
• Laser micromachining beam delivery systems requiring consistent intensity profiles over extended working distances
• Quantum optics experiments involving photon pair generation, where wavefront purity affects entanglement fidelity
• Calibration of wavefront sensors (Shack-Hartmann, pyramid) and spatial light modulators (SLMs)
• Integration into FDA-regulated medical laser devices—documentation package supports 21 CFR Part 11 audit readiness

FAQ

Is the BAM25-175-B-632 suitable for pulsed laser applications beyond 532 nm?
Yes—while the coating is optimized for 600–1050 nm, the fused silica-compatible AR layer maintains < 0.5% average reflectance at 780 nm and 1064 nm. However, laser-induced damage threshold must be re-evaluated per pulse duration and repetition rate; consult Asphericon’s LIDT application note AN-BE-003 for derating guidelines.
Can multiple BAM expanders be cascaded without significant wavefront degradation?
Yes—up to five units may be stacked mechanically. Inter-unit spacing must maintain collimated beam diameter within the clear aperture of downstream elements. Total wavefront error remains below λ/10 RMS (632 nm) when aligned using kinematic mounts with ≤ 2 µrad angular tolerance.
Does Asphericon provide mounting adapters or kinematic solutions for this model?
Yes—standard SM2-threaded lens tubes (LTM25 series) and M28-compatible kinematic mounts (KMB28 series) are available separately. Custom adapter plates with fiducial marks for automated alignment are offered under NRE agreement.
What documentation accompanies the unit for regulatory submissions?
Each shipment includes: (1) Asphericon Certificate of Conformance (CoC), (2) Interferometric Test Report (ITR) with Zernike decomposition, (3) Coating spectral reflectance curve, (4) RoHS Declaration of Conformity, and (5) Material traceability matrix per EN 10204 3.1.
Is there a warranty covering long-term wavefront stability under continuous operation?
Yes—Asphericon warrants RMSi surface stability to < 0.5 µm for 24 months from date of shipment under normal laboratory conditions (non-abrasive environment, no direct UV exposure below 240 nm, relative humidity < 70%).