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LMS manufactures and supplies a wide range of Infra red light emitting diodes with outputs at wavelengths in the 1.3 micron to 7.0 micron range.

These long wavelengths LED's enable solid state optical pollution monitoring to give faster, more accurate information than traditional methods.

Light emitting diodes (LED's) , mounted on TO-18 headers for room temperature operation, TO-8 headers with thermoelectric coolers and special dewars for liquid nitrogen cooling.

The mounting of several LED's on a single TO-type header, each with a different wavelength, allows simultaneous monitoring of different pollutants.

The benefits of infrared LED's include analytical instruments with no moving parts, reduced power consumption and solid state reliability.

Infrared LED's operating at long wavelengths can be used in analytical instruments, portable monitors and medical equipment with all the advantages of LED technology.

The different wavelengths are employed specifically for the following applications:
{short description of image} LED-18: 1.8 micron LED for water vapour

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LED-28: 2.8 micron LED for water vapour

{short description of image} LED-33: 3.3 micron LED for hydrocarbons

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LED-34: 3.4 micron LED for hydrocarbons

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LED-38: 3.8 micron LED for nitrous oxide

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LED-42: 4.2 micron LED for carbon dioxide

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LED-47: 4.7 micron LED for carbon monoxide

{short description of image} LED-6: 6.0 micron LED Broad band IR source

LED's Performance at Room Temperature
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Unique mid-infrared wavelength LED's offer a wide range of new applications

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Sub-microsecond rise time - for faster system response times

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Solid state IR source - low power consumption, narrow bandwidt, bettere liability

LED's Applications
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Measuring impurities in liquids or gases

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Monitoring trace gases in the atmosphere

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On-line control of chemical, industrial, and horticultural processes

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High frequency modulation for use in communications and information processing

Optics / Beam Divergence
All LMS infrared LED's are surface emitting diodes, using a mesa structure. Typical emitting angle is ± 30°; this emitted beam can be focused to typically ± 10° by using either a quartz or sapphire lens. Usage Infrared LED's can operate at high frequencies, improving the signal-to-noise ratio, but beware of reduced lifetime of the LED if it exceeds the "envelope" of current and duty cycle. The duty cycle is typically only 2.5% - 5% to reduce self-heating and power consumption. Use a fast detector when designing with short duty cycles. Increase the frequency and number of averaged measurements to improve your signal-noise ratio. The LED substrate temperature will increase if you increase the power and duty cycle. Ensure that the LED is thermally connected through a good heatsink to improve lifetime and performance. Duty cycle, pulse current and frequency: all three of these parameters are adjustable with our LED-PG infrared emitter Pulse Generator.

The efficiency (and output power) from these LED's increases rapidly with decreasing temperature. If the extra cost is justifiable, then either thermoelectrically cool or use a liquid nitrogen dewar. Remember that coolin shifts the peak to lower wavelengths.
Power increases by (typically) fourfold when using a two stage thermoelectric cooler and tenfold when cooling from room temperature to liquid nitrogen temperature.
Ensure that the LED is thermally connected through a good heatsink using heat sink compound to dissipate excess heat away and improve LED lifetime.

Thermoelectric Cooling
We offer single, two and three stage thermoelectric cooling; for temperature control, use our state of the art microprocessor controlled TE-TC temperature controller.

State of the art Temperature Controller

Liquid Nitrogen Cooling
All LED's can be supplied mounted on a cold finger in an aluminium dewar for operation at 77° K.
Standard hold time is eight hours with special twelve hour dewars as options. Dewars are supplied with a choice of optical windows.
Window materials available are:

Window material 50% Transmission cut-off wavelength (micron)
Quartz 2.2
Sapphire 5.5
Calcium fluoride 7.0
Zinc sulphide 16.0
Germanium 18.0
Zinc selenide 22.0

Liquid Nitrogen Dewars

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{short description of image} TO-18 with window / lens cap or TO-5 with window cap for room temperature operation.

{short description of image} TO-8 with window cap for thermoelectrically cooled operation.
{short description of image} Aluminium dewar for 77°K operation.

TO Style Package