With the continuous upgrading of high-power continuous-wave lasers, pulsed lasers, and high-energy laser systems toward ultra-high flux, long service life and high precision, the core performance requirements for optical substrates have evolved from basic light transmittance to comprehensive capabilities including thermal shock resistance, low deformation, laser damage resistance and long-term operational stability. Benefiting from excellent thermal and mechanical properties, fused silica has become the only widely applicable optical substrate material for large-scale deployment in high-power laser systems. Its thermomechanical parameters, internal defect control level and laser damage resistance directly determine the power ceiling and service life of the entire laser system.
In terms of thermal performance, fused silica substrates exhibit far superior ultra-low thermal expansion characteristics compared with traditional optical glasses. At room temperature of 20°C, its coefficient of thermal expansion (CTE) is merely 0.5×10⁻⁶/K, far lower than conventional materials such as BK-7 optical glass, borosilicate glass and window glass, delivering exceptional temperature stability. Meanwhile, according to the viscosity-temperature characteristic curves, fused silica features a softening temperature of 1730°C, a glass transition temperature of 1200°C, and a maximum operating temperature of 1150°C, which significantly outperforms other optical glass materials.
 

Figure 1: Comparative viscosity-temperature characteristic curves of various optical glasses
 
During long-term irradiation by high-power lasers, temperature gradients form locally on the substrate surface. The ultra-low thermal expansion coefficient effectively restrains thermal deformation of the material, avoids wavefront distortion and beam offset, and ensures high-precision laser output.
Despite excellent thermal stability, fused silica substrates still retain trace intrinsic absorption. Under ultra-high-power laser irradiation, cumulative heat generated by minor bulk absorption induces the thermal lens effect. Local temperature rise causes subtle changes in the refractive index of the substrate, distorts the wavefront of transmitted laser beams, and alters beam focusing position and spot morphology, which seriously impairs the focusing accuracy and energy distribution uniformity of laser systems. To address this latent defect, the industry adopts high-precision common-path photothermal interferometry. Combined with Hartmann-Shack wavefront sensors, this technology accurately captures tiny wavefront distortions caused by the thermal lens effect, reversely calculates the bulk absorption coefficient of substrates, and realizes precise quality control for high-power laser-grade substrates.
 

Figure 2: Experimental setup for substrate absorption measurement based on Hartmann-Shack sensor
 
This detection method has become a mandatory factory inspection indicator for high-end laser substrates.
In terms of mechanical performance, the mechanical strength of fused silica substrates presents typical statistical characteristics, affected by multiple factors including material purity, surface processing quality, internal microcracks and clamping stress. Its tensile strength, flexural strength and compressive strength show significant data dispersion, making theoretical parameters insufficient for performance evaluation. In laser system structural design, concentrated local stress during substrate clamping must be avoided; otherwise, secondary stress birefringence will be induced to cause beam polarization distortion, and even substrate cracking and failure in extreme cases. The industry generally adopts the Weibull statistical model to evaluate substrate strength distribution and failure probability through repeated mechanical tests, providing reliable mechanical parameter support for engineering applications.
Laser damage prevention and control is the core management priority and key technical barrier for high-power fused silica substrates. With the continuous improvement of laser energy flux and irradiation intensity, internal defects such as bubbles and inclusions have become the main triggers of laser damage. Tiny bubbles and impurity inclusions inside substrates modulate laser beam intensity, resulting in local light intensity far exceeding the system design threshold. This excites plasma microbubbles, triggers bulk material damage, and even causes cascading damage on the rear surface of optical elements, leading to overall laser system failure.
The traditional DIN 58927 standard, which allows ignoring microbubbles smaller than 80 μm, is no longer applicable to modern high-energy laser systems. The high-end laser industry has established stringent defect control specifications: no bubbles or inclusions with a diameter larger than 10 μm are permitted in qualified fused silica substrates. Leading manufacturers achieve full-aperture defect detection with 5 μm resolution, completely eliminating laser damage risks caused by micro-defects. In addition, long-term ultraviolet laser irradiation continuously generates color center defects inside substrates and gradually increases transmission loss. Hydrogen loading modification technology can effectively passivate photoinduced defects, significantly improving the laser-induced damage threshold (LIDT) and long-term service stability of substrates.
 

 
JXT provides full-band adaptable fused silica substrates, covering a complete range of high-purity UV-grade and ultra-low-OH IR-grade products. We have various standard sizes in stock and support customized tailoring of thickness, specifications, and optical parameters. We can precisely match process-specific substrates for ultraviolet, infrared, and spectral detection scenarios, and provide complete factory spectral test reports. Our products are widely applicable to the R&D and mass production of various high-precision optoelectronic devices.