What is the SLE system and what dual processes does it integrate?

This ultrafast laser platform integrates two complementary processes: laser micro-milling for precise surface structuring and Selective Laser-Induced Etching (SLE) for true 3D internal fabrication. Femtosecond pulses locally modify glass at the focal volume through nonlinear absorption, enabling selective chemical etching of only the laser-modified regions. The result is the ability to form high-aspect-ratio channels, cavities, and waveguides inside transparent substrates while also performing surface milling and texturing. Advanced multi-axis motion and SLE-optimised software ensure micron-level alignment, depth control, and consistent outcomes across complex geometries.

What is the physics of the SLE process — how does a laser modify glass inside without breaking the surface?

In conventional laser-matter interaction at moderate pulse energies, a focused laser beam is absorbed at the material surface where the photon energy exceeds the material’s single-photon absorption threshold. For transparent materials like fused silica and borosilicate glass — which have bandgaps of 8–9 eV and are transparent to all wavelengths from UV through near-infrared — single-photon absorption does not occur at 1030 nm or 515 nm wavelengths, meaning the laser beam propagates through the glass without depositing energy until it reaches the focus. At the focal volume, the local intensity becomes extremely high — for femtosecond pulses at the peak powers used in SLE processing, the intensity at focus can reach 10^13 W/cm² or above — at which point nonlinear multi-photon absorption (absorbing 3–5 photons simultaneously to bridge the bandgap) and tunnel ionisation deposit energy in a highly localised zone at the focal point. This creates a structurally and chemically modified region — with altered density, changed chemical bonding, and increased solubility in etchants — confined to a few cubic micrometres at the focus, while the glass above and below the focus remains completely unaffected. The selectivity of subsequent KOH or HF etching between laser-modified and unmodified glass — with etch rate ratios of 100:1 to 1000:1 depending on glass composition and laser parameters — ensures that only the laser-programmed volume is removed, leaving clean internal voids whose geometry corresponds exactly to the three-dimensional laser scan path.

Ultrafast Femtosecond Pulse Processing for Volumetric Glass Modification

Ultrashort femtosecond pulses confine energy to the focal volume through nonlinear multi-photon absorption — enabling non-thermal, spatially precise material modification at any depth within the glass substrate without affecting the surrounding material. The femtosecond pulse duration is critical: longer nanosecond or picosecond pulses would generate sufficient thermal energy to cause crack propagation and mechanical damage in the glass around the modification zone, compromising the structural integrity of the unmodified substrate and the quality of the etched features. Femtosecond pulses create chemically modified regions without thermal stress — producing modification zones whose boundaries are defined by the nonlinear intensity threshold rather than by thermal diffusion extent, enabling the sub-micrometre feature definition that the SLE process requires.

True 3D Internal Structuring — Unique Capability in the Product Range

SLE creates enclosed channels, overhangs, multi-level cavities, and freeform 3D structures inside glass — capabilities not achievable with any surface machining technique. This true 3D internal fabrication capability is the defining unique feature that places the SLE system in a separate capability category from all other laser micromachining platforms in the product range. Enclosed microfluidic channels — with rectangular, circular, or arbitrary cross-section geometries, junctions, valves, and mixing structures — are formed inside a single, uncut substrate without any bonding step. Buried optical waveguides — whose refractive index is permanently modified by the laser exposure — are written at programmed depths within the glass volume without any surface access. Multi-level internal networks — with channels at different depths connected by vertical vias — are fabricated by programming the laser scan path through multiple depth planes in the software. None of these structures can be fabricated by any other process in this range.

Precision Laser Micro-Milling for Integrated Surface and Internal Fabrication

The Akoneer system also performs high-resolution surface milling and texturing — delivering smooth finishes, sharp edges, and accurate depth control for micro-optical and fluidic interfaces on the substrate surface — alongside the SLE internal structuring capability. This dual-process integration means that a complete lab-on-chip device can be fabricated in a single workflow: SLE processes the internal microfluidic network, inlet and outlet ports, and mixing chambers within the substrate volume, while surface micro-milling defines the optical access windows, connection port geometries, and surface alignment features on the substrate faces. The ability to precisely register surface features to internal structures — within the system’s sub-1 µm accuracy — is the key advantage of integrating both processes on the same platform rather than performing them on separate machines.

High Aspect Ratio Capability Exceeding 20:1

Supports internal structures with aspect ratios — channel depth to channel width — exceeding 20:1, enabling the high-aspect-ratio channels, vias, and capillary arrays required by microfluidics, MEMS, and optical interconnect applications. Achieving 20:1 aspect ratio in glass internal structuring requires a combination of very small focal spot diameter (for narrow feature width), sufficiently long working distance objective (for deep Z-range without spherical aberration degradation), and etch selectivity high enough that the etchant can penetrate the full channel depth without consuming the unmodified glass walls. The Akoneer system’s high-NA optics, adaptive aberration correction for deep focusing, and optimised laser-glass parameters deliver this 20:1 capability consistently across the full working area.

Three-Wavelength Laser Source Configuration

The system offers selectable IR (1030 nm), green (515 nm), and UV (343 nm) wavelengths — individually, as two-wavelength combinations, or all three simultaneously. Multi-wavelength capability allows the laser parameters to be optimised for each glass composition and processing task: 1030 nm for maximum power efficiency and deep focusing in glasses with low linear absorption at IR wavelengths; 515 nm for glass compositions with stronger green absorption or where a smaller focal spot is needed for finer feature sizes; 343 nm UV for the finest feature resolution at short wavelength and for glass compositions where UV absorption enhances modification efficiency. Simultaneous dual- or triple-wavelength operation enables advanced processing strategies — combining IR for bulk modification with UV for surface micro-milling in the same scan pass — that are not possible with single-wavelength systems.

Maskless, Single-Step Manufacturing Workflow

SLE eliminates photolithography masks and the associated cleanroom infrastructure — patterning is programmed directly in the CAD/CAM software and written by the laser without physical mask fabrication, alignment, exposure, development, or stripping. This maskless manufacturing workflow reduces cost per substrate, eliminates the lead time of mask fabrication, and allows design changes to be implemented by software modification rather than by new mask procurement. For R&D environments where design iteration is frequent and batch sizes are small, maskless SLE is dramatically more agile than mask-based wet etching. For production environments, maskless operation eliminates the mask management complexity and contamination risk of photolithography in the same cleanroom where sensitive optical and biological substrates are processed.

Microfluidics and Lab-on-Chip

The SLE system’s true 3D internal glass structuring capability is uniquely suited to microfluidic device fabrication — enabling fully enclosed, leak-tight microchannels, passive mixers, multi-level channel networks, valves, and chambers inside single glass substrates without bonding separately fabricated layers. SLE-fabricated glass microfluidic chips offer the chemical inertness, optical transparency, and surface chemistry control of glass — advantages over PDMS polymer chips for analytical applications requiring organic solvent compatibility, elevated temperature operation, or UV-transparent optical access — combined with the 3D geometry freedom of the SLE process that enables device architectures not achievable in glass by any other method. Applied for organ-on-chip co-culture chambers, DNA analysis chips, single-cell isolation arrays, droplet microfluidics platforms, and high-throughput drug screening chips where glass substrate properties are required alongside complex 3D internal architecture.

Photonics and Integrated Optics

SLE enables creation of buried waveguides, directional couplers, and hybrid photonic-fluidic structures within glass substrates — with precise refractive index control through the laser modification parameters. Laser-written buried waveguides in fused silica and borosilicate glass are formed when femtosecond laser exposure permanently modifies the local refractive index — creating a waveguide core region with higher refractive index than the surrounding unmodified glass, without any subsequent etching. These laser-written waveguides are the basis for integrated photonic circuits in glass: splitters, multiplexers, interferometers, and sensing waveguides fabricated entirely inside the glass volume. When combined with SLE-etched microfluidic channels in the same substrate, the result is an optofluidic chip — a photonic-fluidic hybrid device where laser light propagates in the buried waveguide alongside a microfluidic channel for evanescent wave sensing, fluorescence detection, or absorption spectroscopy — the most sensitive format for lab-on-chip chemical and biological analysis.

Biomedical and Analytical Devices

SLE enables the fabrication of microchambers, capillary arrays, and transparent fluid pathways required for implantable diagnostics, drug delivery devices, and chemical synthesis microsystems. Glass is the substrate of choice for implantable photonic biosensors — its chemical inertness, biocompatibility with appropriate surface treatment, and optical transparency at both visible and near-infrared wavelengths make it the only material suitable for long-term implanted optical sensing. SLE fabricates the sealed microfluidic channels and optical coupling windows of these devices within a monolithic glass body — eliminating the bonded interfaces that are the primary failure mode of multi-chip biomedical microdevices under the mechanical loads of implantation and in-vivo use. Applied for continuous glucose monitoring implant chips, intraocular pressure sensing devices, neural recording optofluidic probes, and drug-loaded microchannel arrays for controlled in-vivo drug delivery.

MEMS and High-Aspect-Ratio Glass Components

SLE produces internal supports, precision cavities, and hermetic features for glass MEMS sensors, optical MEMS assemblies, and glass encapsulation structures. Glass MEMS applications include resonant mass sensors (where glass’s low intrinsic damping maximises resonance quality factor), optical MEMS (where glass’s transparency and low absorption at working wavelengths is required for integrated optical readout), and glass-capped MEMS packages (where the hermetic glass-to-silicon bond provides the vacuum environment required for high-Q resonator performance). SLE fabricates the precision cavities, etch-stop features, and high-aspect-ratio coupling apertures in glass MEMS components with the accuracy and internal geometry freedom that conventional glass machining methods cannot provide.

Advanced Optics and Diffractive Elements

SLE enables free-form micro-optics, phase plates, beam shapers, and diffractive optical elements integrated within glass substrates — fabricating optical elements with 3D refractive profiles that can only be produced by combining surface micro-milling (for surface relief features) with internal refractive index modification (for volumetric phase elements). Integrated micro-lens arrays with buried focusing elements, multi-level diffractive beam shapers with internal depth-coded phase profiles, and hybrid refractive-diffractive optical systems are all achievable. These embedded optical elements are protected from surface contamination, mechanical damage, and environmental effects by the surrounding unmodified glass — a significant reliability and performance advantage over equivalent surface-relief optical elements in harsh optical environments.

United Spectrum Instruments, the official distributor of Akoneer systems in India, delivers advanced ultrafast laser platforms for micro-milling and SLE applications. We support customers across India with application consultation, sample validation, system integration, and training to ensure smooth deployment. With deep expertise in femtosecond laser processing and glass microfabrication, we enable reliable results and scalable production.

Official Akoneer Distributor with Deep Femtosecond Glass Microfabrication Expertise

As the official Akoneer distributor in India, United Spectrum Instruments provides end-to-end SLE application support — from pre-purchase feasibility assessment of your 3D glass structure requirements through system installation, etchant chemistry consultation, SLE process recipe development, and long-term technical service. Our understanding of the SLE process physics — nonlinear glass modification, etch selectivity optimisation, aspect ratio limits, and waveguide writing parameters — enables process development consultation at the depth required for successful deployment of this advanced glass microfabrication technology in both R&D and production environments.

• Official distributor in India for Akoneer ultrafast laser micro-milling and SLE systems — genuine products with full manufacturer warranty and direct manufacturer process engineering support coordination.
• Strong expertise in femtosecond laser processing and glass microfabrication — our engineers understand SLE nonlinear absorption physics, etch selectivity optimisation for different glass compositions, aspect ratio limits, optofluidic device design, and waveguide writing parameters.
• Application consultation, sample validation, system integration, and operator training — we assess your 3D glass structure requirements, arrange sample fabrication trials before purchase, configure the system for your substrate formats, and provide comprehensive operator and process engineer training at your facility.
• Nationwide service and long-term technical support — India-wide AMC coverage including system calibration, laser source performance monitoring, optics cleaning and alignment, and emergency on-site support to maintain SLE process quality across the system’s operational lifetime.