Does the high temperature resistance of UV quartz lenses meet the requirements for use?

UV quartz lens is a core component in UV optical systems, widely used in fields such as laser processing, photolithography technology, medical disinfection, environmental monitoring, etc. Its performance directly affects the accuracy, efficiency, and stability of the system, and high temperature resistance is one of the key indicators to measure its applicability. This article will analyze whether the high temperature resistance of ultraviolet quartz material meets the requirements from the aspects of its characteristics, quantitative standards for high temperature resistance, and matching of practical application scenarios.

1、 Material characteristics and high-temperature resistance basis of ultraviolet quartz lens

The substrate of ultraviolet quartz lens is quartz glass (mainly composed of silicon dioxide, SiO ₂), which can be divided into ordinary quartz glass (containing a small amount of impurities) and fused silica glass (purity ≥ 99.9%) according to purity. The high temperature resistance of quartz glass is attributed to its unique molecular structure: silicon dioxide molecules form a three-dimensional network structure through covalent bonds, with a bond energy of up to 452 kJ/mol, much higher than that of ordinary glass (such as sodium calcium glass, which has a Si-O bond energy of about 360 kJ/mol), thus possessing excellent high temperature stability.

High temperature resistance parameters of fused silica glass:

The softening point of fused silica glass is about 1650 ℃, and the working temperature can be stabilized below 1000 ℃ for a long time; During short-term (several hours) use, the temperature tolerance can be increased to 1200 ℃. Its coefficient of thermal expansion is extremely low (about 5.5 × 10 ⁻⁷/℃), only 1/20 of ordinary glass, and it is not easily cracked due to thermal stress under severe temperature changes (excellent thermal shock resistance).

Limitations of ordinary quartz glass:

If it contains impurities such as aluminum, iron, sodium, etc., it will reduce its high temperature resistance, and the softening point may drop below 1500 ℃. It is recommended not to exceed 800 ℃ for long-term use, otherwise the optical performance may deteriorate due to impurity migration (such as a decrease in transmittance).

2、 Quantitative evaluation standard for high temperature resistance of ultraviolet quartz lenses

To determine whether the high temperature resistance of ultraviolet quartz lenses meets the requirements, the following quantitative indicators should be considered:

Short term high temperature stability

In an instantaneous high-temperature environment (such as local high temperature generated by laser focusing), the lens needs to avoid optical path deviation caused by thermal deformation. The thermal conductivity of fused silica is about 1.4 W/(m ・ K), which is lower than that of metal. However, in the UV optical system, the temperature can be effectively controlled by designing a heat dissipation structure (such as a water-cooled jacket and a heat sink). For example, in the laser welding scene, the instantaneous temperature at the focal point of ultraviolet laser (such as 355 nm) can reach thousands of degrees Celsius, but the lens can control its own temperature below 200 ℃ through a cooling system, far below its softening point and with stable performance.

Long term high temperature resistance and reliability

For continuous high temperature environments (such as industrial furnace ultraviolet monitoring systems), the lens needs to withstand temperatures of 100-500 ℃ for a long time. When fused silica is used for a long time below 500 ℃, the transmittance (200-400 nm in the ultraviolet band) attenuation rate is less than 1%/year; Even when working continuously at 800 ℃, the attenuation of light transmittance can still be controlled within 5% (based on 1000 hours of test data), meeting the needs of most industrial scenarios.

Thermal deformation and optical accuracy retention

Thermal deformation at high temperatures can cause changes in the curvature radius and thickness of the lens, affecting imaging or focusing accuracy. The elastic modulus of fused silica is about 72 GPa. When the temperature is below 1000 ℃, the thermal deformation is very small (for example, the thermal expansion of a lens with a diameter of 50 mm is only about 0.00275 mm when the temperature is 500 ℃). The influence on the optical accuracy can be ignored. However, the deformation of ordinary glass at 200 ℃ is more than 10 times that of quartz, which cannot meet the high-precision requirements.

Thermal shock resistance performance

In scenarios of sudden temperature changes (such as rapidly entering an environment of 300 ℃ from room temperature), the lens should avoid cracking. The thermal shock resistance temperature difference of fused silica (the temperature change that can be withstood instantaneously) can reach more than 300 ℃, while that of ordinary glass is only 50-100 ℃. For example, in the ultraviolet detection system for automobile exhaust, the lens needs to frequently withstand the alternation of high exhaust temperatures (200-400 ℃) and low environmental temperatures. The thermal shock resistance of quartz lenses can effectively reduce the risk of damage.

3、 Requirement matching analysis in practical application scenarios

Whether the high temperature resistance of ultraviolet quartz lenses meets the requirements depends on the temperature conditions of specific application scenarios:

Low to medium temperature scenarios (<300 ℃): fully compatible

Medical disinfection: The working temperature of UV disinfection cabinets is usually 50-80 ℃. Quartz lenses have no degradation in performance in this environment and are resistant to ozone corrosion (ozone is generated by UV exposure to air), which is better than plastic or ordinary glass lenses.

Environmental monitoring: The working temperature of the atmospheric ultraviolet spectrometer is -30-60 ℃, and the wide temperature stability of the quartz lens (-200-1000 ℃) can meet the requirements of extreme outdoor environments.

Medium high temperature scenario (300-800 ℃): Good adaptability

Ultraviolet temperature measurement of industrial furnace: the temperature in the furnace is above 1000 ℃, but the lens can control its own temperature below 500 ℃ through water cooling design, and the transmittance and shape stability of fused silica have no obvious changes.

UV curing equipment: The temperature near the curing lamp is about 300-500 ℃, and the quartz lens can withstand it for a long time. The transmittance of the UV band (such as 254 nm, 365 nm) is greater than 90%, which is much higher than that of ordinary glass (transmittance<50%).

High temperature scenario (800-1200 ℃): limited adaptation

Ultraviolet monitoring of aeroengine: when the temperature near the engine combustion chamber reaches 1000 ℃, a specially made fused silica lens is required to work together with an active cooling system (such as liquid nitrogen cooling), which can work stably for a short time (several hours). However, long-term use may lead to a decline in light transmittance (about 10% annually) due to lattice relaxation.

Laser cutting of thick metal: When the temperature at the focal point reaches over 2000 ℃, the lens needs to be controlled below 800 ℃ through efficient water cooling, otherwise micro cracks may occur due to local overheating.

Ultra high temperature scenario (>1200 ℃): insufficient adaptability

If the system cannot control the lens temperature through cooling (such as non-contact high temperature melt UV detection), when the temperature exceeds 1200 ℃, fused silica will soften significantly, resulting in loss of optical accuracy. At this time, it is necessary to use materials that are more resistant to high temperature (such as sapphire, melting point 2050 ℃). However, sapphire has low transmittance in the UV band (almost no transmittance below 200 nm), so it is necessary to make a trade-off.

4、 Optimization measures to enhance high temperature resistance performance

To further adapt to high-temperature scenarios, the high-temperature resistance of UV quartz lenses can be optimized through the following methods:

Material purification: ultra-high purity fused silica (impurity content<1 ppm) is used to reduce impurity diffusion under high temperature and improve long-term stability.

Surface coating: Coating with high temperature resistant anti reflective film (such as hafnium dioxide HfO ₂ film, melting point 2758 ℃), which not only enhances UV transmittance but also improves surface resistance to high temperature oxidation.

Structural design: Adopting irregular lenses (such as wedge-shaped or non spherical) to reduce heat accumulation areas, or integrating microchannel heat dissipation structures to improve heat dissipation efficiency.

5、 Conclusion: In most scenarios, it meets the usage requirements, but special design is required for extreme high temperatures

The high temperature resistance of ultraviolet quartz lens (especially fused silica material) meets the requirements in most application scenarios:

Under 1000 ℃, with reasonable heat dissipation design, it can work stably for a long time, meeting the needs of medical, industrial, environmental monitoring and other fields;

In short-term high temperature scenarios of 1000-1200 ℃, limited adaptation with cooling systems is possible, but regular optical performance testing is required;

In ultra-high temperature environments exceeding 1200 ℃, its performance is insufficient and needs to be replaced with more heat-resistant materials such as sapphire, but it must accept the loss of ultraviolet transmittance.

Therefore, the high temperature resistance of UV quartz lenses is "scene adaptive" - within its designed temperature range (usually ≤ 1000 ℃), it fully meets the usage requirements, and its comprehensive optical performance (UV transmittance, accuracy, thermal shock resistance) is superior to other materials, making it an optional component of UV optical systems.