Hamamatsu News 2-2016 - page 6

News 2016 Vol. 2
6
Figure 1: Absorption wavelengths of gases
Hamamatsu provides light sources used to measure gases that absorb light in the mid-infrared range (3 μm to 10 μm).
Mid IR range
aromatics
CH
4
CH
4
CH
4
SO
2
SO
2
NO
NO
O
3
glucose
NH
3
NH
3
H
2
S
H
2
S
H
2
S
acetone
SO
3
SO
3
CO
2
CO
2
CO
2
H
2
O
H
2
O
NO
2
N
2
O
N
2
O
N
2
O
CO
CO
NH
3
NH
3
NH
3
HF HF
O
2
SF
6
aromatics
ethylene
Wavelength (µm)
0.5 1
2
3
4
5
6
7
8
9
10
11
12
13
14
R&D Interview
Technical process to provide both light sensors
and light emitters needed for gas analysis
What are the special features offered by optical measurements
in the mid-infrared range?
Oishi:
Techniques such as gas chromatography and mass spectrometry
are used for making gas measurements and these involve obtaining
a sample of the target gas and measuring it inside a measuring
instrument. However, the optical measurement using a laser offers the
advantage that you can make measurements by directly applying the
laser to the target gas. That means you don’t have to bring the test
object into a laboratory, so you can make measurements in the field
or right on the production line at the worksite. This vastly broadens
the possible applications.
Sugiyama:
Here at Hamamatsu Photonics we have provided lasers
used to measure gases in the mid-infrared spectral range. Gases we
can now measure in the wavelength range of about 3 μm to 10 μm
include methane gas, carbon dioxide, carbon monoxide, sulfur oxide
and nitrogen oxide, and so on. (See Figure 1)
Did you face any challenges in developing light sensors and light
emitters for the mid-infrared range?
Sugiyama:
Well, the reason why we were interested in the gas mole­
cules in the mid-infrared region is that many gases or gas molecules
strongly absorb the mid-infrared light. This is advantageous to make
measurements.
Iida:
On the other hand, the background light that may enter the
detector becomes brighter in the mid-infrared range, so light other
than what you want to detect is also sensed. This becomes a noise
component and causes problems in light detection. Moreover, in this
wavelength range, manufacturing an ideal light sensor with sufficiently
high sensitivity is very difficult. This makes it essential to enhance
the light emitter performance as well as to increase the mid-infrared
sensitivity of the light sensor. Parallel development that boosts the
performance of both devices is where one sees the true value of
Hamamatsu Photonics.
Quantum cascade laser (QCL)
Emission of mid-infrared
laser beam
InAsSb photovoltaic detector
Measurement of light power after
transmittance through gas
Gas output
Gas input
Figure 2: Schematic diagram of trace gas analysis using a light emitter (QCL)
and light sensor (InAsSb photovoltaic detector)
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