Ultraviolet (UV) Optics/Detectors: For Solar-Bind Imaging & Detections Application Note

When high-voltage equipment discharges electricity, corona discharge, arc flash, or arc discharge may occur depending on the electric field strength, during which electrons in the air continuously gain & release energy, emitting UV rays. UV imaging utilizes this principle to receive UV signals. UV optics are involved in solar-bind imaging. Solar radiation in the wavelength band of 190-285nm is completely absorbed by the ozone layer when passed through the atmosphere. The scattering of other components & the surface ozone in the atmosphere below the ozone layer also absorbs it, creating a natural “solar-blind” near the ground – where the naturally occurring solar signal is almost completely undetectable

Operation Principle

UV Lens

In UV imaging, UV light signals released are processed & overlapped with the image formed by visible light on a screen, allowing for the position & intensity of the electrical discharge to be determined. Our UV lens is developed for use across x-rays & visible light within the electromagnetic spectrum. Our UV lens has a wavelength over a range from 200nm to 385nm. Its apochromatic lens allows images to be formed across UV to visible light spectrums. It can be used in UV cameras or image intensifier tubes for observation. The addition of a close-up lens allows for obscure fingerprints on surfaces of materials, such as glass, to be detected & efficiently removed.

UV Lens Detectors 1
Figure 1. Photos of typical UV lens assembly
ModelRange
Fixed Focus LensEFL: 10 ~ 300 mm
Zoom Lens (1.5x)EFL: 40 ~ 60 mm
Super Achromatic LensWavelength: 200 ~ 1100 nm
Table 1. Model Ranges

UV lenses encompass features of chase light caliber, & high accuracy & resolution. In solar-bind imaging, the existence of light in the solar blind ultraviolet band on the earth usually consists of only three cases: (1) an unnatural danger signal, such as gunfire, explosive explosion, fire & corona generated by high-voltage transmission line leakage; (2) a man-made solar-bright ultraviolet light source; (3) abnormal weather such as strong lightning. This entails that if a solar blind UV signal is detected in the “dark room”, a specific event, such as a missile attack, occurs.

The area within 15 km of the surface layer is free from noise interference, allowing for the target to be detected without sophisticated image processing.

UV Lens Detectors 3
Figure 2. The layout of UV 90-degree wide-angle lens

The key specifications of the UV wide-angle lens are listed below. Compared to similar products in the market, we offer small wide-angle distortion and better pixel resolution, useful for solar-blind imaging and detection.

Wavelength254+/-20nm
Focal Length9.2mm
BFL13.5mm
ApertureF#3.6 (manually tunable)
FOV (Imaging Plane)18mm
FOV (Angle)90°
Working Distance20cm ~ ∞
Angle Distortion</=2%
MTF70Ip/mm>0.3
MountC-mount
Working Temperature-40 ~ 50 °C
Table 2. Key specifications of one type of UV lens

UV Detectors

UV detectors include a UV image intensifier tube, UV ICCD/ICMOS, and solar-blind UV filter components. These are critical assemblies to form the hard core of a UV imaging/detection system. Combining the capabilities of UV detectors and UV lens/optics, we are able to offer customization solutions for different applications.

UV Lens Detectors 5
Figure 2. UV detectors assembly components

Applications

UV imaging technology could be used in but not limited to the following application scenarios:

  • Ship fog breaking piloting
  • Forest fire alarm
  • Power grid safety monitoring
  • Maritime search and rescue
  • Satellite navigation
  • Aircraft fog breaking blind drop
  • Missile approach warning
  • Document security feature identification under sunlight conditions (passport, license, etc.)
  • Close-range criminal investigation; search for potential fingerprints, footprints, hidden blood prints, fibers, etc

In power & high-speed rail systems, UV imaging could be used to achieve high-sensitivity corona and arc detection as shown in Fig. 3 left; 100% filtered out of the sunlight during full-day blindness, to achieve high sensitivity corona and arc detection.

UV Lens Detectors 7
Figure 3. Applications of solar-bind UV imaging

Another critical application is the forest fire alarm. Compared to existing fire alarm technology which cannot penetrate the “dark room” atmosphere under sunlight, UV imaging provides solar blindness adaptability. Secondly, it is not affected by environmental/weather changes and high-temperature interference sources. Utilizing high-sensitivity UV imaging technology, the occurrence of a fire in real-time can be detected several kilometers away. It can be covered by setting up a gimbal (as shown in Fig. 3 right) or installing it on a helicopter to cover the entire forest area.

Wavelength185 – 330nm
Peak Response245nm
Diameter of Cathode18-25mm
Irradiation Sensitivity40 mA/W@254nm
Resolution20lp/mm
Background Irradiation5×10-11W/m2
Irradiation Gain108(cd/m2)/(W/m2)
Size (mm x mm)Φ35.5 x17.6/Φ45.5 x18
Working Temperature-55 to 70 °C
Table 3. Key specifications of UV intensifier tube
Parameters18-ICCD25-ICCD
Wavelength185 – 330 nm185 – 330 nm
CCD SizeHalf inchHalf inch
CCD Pixels752 x 582752 x 582
Magnification1:2.21:3.1
Resolution1515
Sensitive Area14mmx10.5mm20mmx15mm
Output signalComposite Video
/ethernet100fps
Composite
Video
Input VoltageDC 12, 5DC 12, 5
Working
Temperature
-25 to 45 °C-25 to 45 °C
Table 4. Key specifications of UV ICCD/ICMOS sensors
Wavelength264 +/-3nm264 +/-3nm264 +/-3nm
Peak
Transmission
>20%>20%>20%
Bandwidth20+/-3nm20+/-3nm20+/-3nm
SerialRMF-ARMF-BRMF-C
SizeΦ31.5
x21.5
Φ31.5
x26.3
Φ37
x21.5
ApertureΦ22.5Φ22.5Φ30
Mass<40g<50g<60g
Working
Temperature
-40 to 60
°C
-40 to 70
°C
-40 to 60
°C
ReliabilityGJB-369A-98 and GJB-150GJB-369A-98 and GJB-150GJB-369A-98 and GJB-150
Table 5. Key specifications of solar-blind UV filters

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