It is a contactless measurement where the temperature is based on the irradiance (thermal radiation) from the sample onto a detector.

Pyrometers operate by comparing the spectrum of the light from the observed object and comparing it against a known standard.

The spectral content of blackbody radiation depends only on the temperature of the body. We all know this, in a sense, by experience: cool objects do not glow, warm ones glow a dull red, and then the colour changes through orange, yellow, etc. What your eye is doing is picking up the principal emission of the object - and the wavelength of that emission varies inversely with absolute temperature.

So. A pyrometer can monitor discrete wavelengths, compare their relative intensities, and from that ratio (if the emissivity is a constant for all wavelengths) the absolute temperature can be deduced.

In a manner of speaking, pyrometry *does* depend on intensity, but not the total integrated intensity, rather the power radiated as a function of wavelength. The shape of that plot is what determines the absolute temperature.

Anyway, pyrometers are available as spectral pyrometers, broad band pyrometers and also total wavelangth pyrometers. In any case you either have to compare at least to different and adequately distanced wavelengths (the signals) in order to assess the emissivity or you may do know the respective emissivity to which the device is then adjusted.

For linear pyrometers where the signal i.e. typically a photo current is linear against the total radiation corrections of the measurment with respect to wrong or wrongly adjusted emssivities are simplified. Given that the readout of the pyrometer was analogous, the measurement can be very fast and may even resolve dynamic processes.

I suggest you look at a Rapid Thermal Anneal (RTA) furnace setup which incorporates the use of an optical pyrometer .. such as https://www.bo.imm.cnr.it/site/?q=node/61

In the picture shown at the site given, the sample to be rapidly thermally heated is placed atop a holder .. ususally of a specific material type .. eg a silicon coated graphite susceptor for a SiC RTA device .. which sits on the top of a 'glass' tube ... shown as a black dish/plate.

The whole assembly is then raised via the sliding bars up into the RTA chamber .. usually an RF coil heater assembly .. and mechanically locked in position with clamps and 'o' ring seals to contain gas flow ...

Sitting at the bottom of the whole assemly one can see a round circular apperture through which an optical pyrometer has .. in effect .. a clear view of the susceptor containing the specimen .. atop of the 'glass' tube assembly.

The 'colour' seen by the optical pyrometer can be interpreted directly to the temperature of the susceptor .. and hence the contained device sample .. and the optical pyrometer sends this 'seen' temperature electronically to the RF coil control heater electronics ... the temperature usually being previously set via a computer interface of some type by an operator.

In operation, gasses are passed through the 'glass' tube assembly according to the heating or RTA cycle requirements ... these gasses .. Nitrogen (N) .. Argon (Ar) .. etc have their respective flow rates controlled and timed by the controlling computer interface ... again previously set by an operator .. when they enter the 'process recipe'.

Again, in operation, the correct sample susceptor needs to be used .. eg graphite covered with a Si coating .. for a SiC sample ... to provide the necessary 'silicon over pressure' .. as this ensures minimal sublimation decomposition of the SiC sample which is known to occur at elevated temperatures ...

This is but one example regarding "How does a pyrometer works in Rapid thermal processing"

I hope this helps you.

Thanks all..