These are some Frequently Asked Questions about Star Tech Instruments ultraviolet energy meters. Feel free to ask more if you have any.
How do they work?
All Star Tech Instruments UV energy probes work by the process of downconversion. Ultraviolet light is converted to the visible or near-IR by one of our proprietary downconversion crystals. The energy is then reemitted in the visible or near-IR spectra and collected using a collection geometry designed to maximize uniformity of response across the probe. The longer wavelength light is then transmitted to silicon photodiodes and converted to an electrical signal proportional to the input energy.
What is the dynamic range?
Star Tech Instruments energy meters use no bias voltage. The maximum linear output signal is 150 mV. There is no minimum; the smallest signal you will be able to read will depend on the precision of your readout device.
The BEM series of energy probes have slide
bars which allow you to optically attenuate the probe
responsivity over four orders of magnitude. The responsivity of
other probes is adjusted electrically. The RS-100 responsivity
switch is a passive device which allows nearly four orders of
magnitude of dynamic range. The ADB-6 (Active Decade Box) is a
rechargeable device which both amplifies the signal and gives six
decades of dynamic range to any Star Tech Instruments
How about the dynamic range of the crystal? Isn't downconversion a nonlinear process?
Of course it is! All natural processes are nonlinear. However, the range over which the input-output relationship approximates a straight line is again around 4 to 5 orders of magnitude, depending on wavelength and choice of material.
What is the damage threshold? Don't the components degrade?
There are three basic types of radiation damage associated with excimer laser energy probes-
Ablation Damage- A focused excimer beam will vaporize any known material, and our instruments are no exception. Ablation damage will occur when the energy density of a pulse exceeds the single-shot damage threshold. This is normally around 500 mJ/cm2 for most of our probes, with versions available having damage thresholds as high as 5 J/cm2
Thermal Damage- Thermal damage occurs when the total optical power of the incident beam exceeds the amount that can be dissipated by the energy probe, and the resulting temperature rise damages the components of the probe. The maximum input power for a Star Tech Instruments energy probe ranges from 5 watts to over 1 kilowatt, depending on model, wavelength, and configuration.
Long-Term Degradation- After hundreds of units and billions of pulses, in-house and field tests of our downconverter plates show that they never deteriorate, when used within their specified energy and power ranges. The downconverter will never have to be replaced because it is "worn out". The silicon photodiodes are isolated from any ultraviolet radiation, protecting them from degradation also.
What is a "low insertion loss" probe?
The downconverting crystals used in our probes are semi-transparent in the ultraviolet and can be made very thin so that they absorb only a very small amount of the incident energy. Theycan then be AR coated, so that the beam can pass right through the probe with minimal loss of energy. Probes are available with energy transmission as great as 99%. This type of probe is normally semi-permanently mounted in an optical train, so that the user can directly measure beam intensity, real-time, during some optical process.
What are the upper and lower limits on responsivity?
We have probes with pulsed responsivity as high as 500000 V/J. On the other end ot the scale, probes have been built with responsivity as low as 0.01 V/J.
What does the output of the energy probes look like?
Although the pulse width of an excimer laser and many other deep UV lasers is very short (typically 5-50 ns) the energy is integrated within the downconverting crystal to produce a much longer, and thus much easier to handle output pulse. Typical output pulse widths are from 0.1 ms to 5 ms, depending on the probe model. The output pulse width is independent of the input pulse width; only the output pulse amplitude changes in proportion to the total pulse energy.
Can these probes be used for CW applications also?
Yes. Our energy probes can be used with CW ultraviolet and soft x-ray sources. They are very stable, and put out a DC current proportional to the input power.
Can they be interfaced to any electronics?
Yes. Star Tech Instruments produces several electronic readouts for our energy probes. In addition, being the output impedances of our probes are low, they can be used with the readouts that are sold for use with passive pyroelectric probes. They can also be read using an oscilloscope, or for CW measurements, a microammeter.
What is the usable wavelength range?
Star Tech Instruments energy probes have been used at all excimer wavelengths from 157 nm to 351 nm, and with other pulsed and CW lasers with wavelengths as long as 400 nm. On the other end of the spectrum, our probes have been used with soft x-ray sources, such as the kind used for x-ray lithography, as short as 1 nm. With such short wavelengths the downconverter needs to be mounted in a vacuum-tight fixture, but being the radiation is then converted to visible light no vacuum is necessary after that point.
What is the maximum repetition rate of the input beam?
Stock energy probes are capable of discerning individual pulses at repetition rates as high as 2 KHz, with probes available which are usable up to 10 KHz.
How large of a beam can I measure?
Stock items have input apertures from 10 mm to 100 mm, and apertures 150 mm or larger are available on special order.
What makes your energy probes so much better than everyone else's?
Our downconversion process is patented and proprietary. Other devices used for measuring UV pulse energy are pyroelectric detectors, and directly-irradiated silicon photodiodes.
Pyroelectric detectors tend to be damaged by the highly destructive beams of excimers. They are microphonic (sensitive to mechanical vibration), bulky, and have high output impedances which make them sensitive to electrical noise. Some large-area models exhibit gross changes in responsivity across the active area.
Some detectors consist of diffusers and attenuators placed directly in front of a silicon photodiode. Silicon photodiodes have been shown to deteriorate when exposed to even very small amounts of UV radiation; furthermore, diffusers and attenuators often exhibit long-term changes in transmission when used in the deep ultraviolet.
Only Star Tech Instruments UV energy probes avoid all of these drawbacks. They are resistant to laser damage even in the most strenuous applications. They are resistant to mechanical and electrical noise. They are compact, sensitive, and versatile. These benefits, coupled with their competitive pricing, make them the best value in ultraviolet energy detection on the market.
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