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Wednesday, Nov. 25, 2015

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'Using Mid-InfraRed Lasers'

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Five Princeton graduate students are leading a yearlong field research project using new laser sensors to measure pollutants with unprecedented sensitivity. Read more.

Video Closed Captions


DAVID MILLER: There are more
people on earth every day.

And they all need to be fed.

This means we have to increase
the amount of agricultural

production on the planet.

But it also means that we have
to increase the nitrogen

fertilizers that
are being used.

This is leading to much larger
emissions of gases such as

nitrous oxide into
the atmosphere.

My name is David Miller, and
I'm helping to coordinate a

student-led independent

Our team of nine engineering
graduate students are working

to develop and deploy fast,
compact, and low-power sensors

based on a new technology,
mid-infrared lasers.

The main goal of MIRTHE is to
build the next generation of

environmental sensors.

As part of MIRTHE's interest in
new ideas and applications,

the center provided a first-time
opportunity for

students to lead and manage
a fully funded

field research project.

MIRTHE and it's director,
Professor Claire Gmachl were

extremely supportive of us.

We design and engineer our
sensors so that the laser can

trace a long path to increase
the sensitivity of our


To do this, we bounce the laser
many times between two

mirrors, which is known as
a multipass optical cell.

So this is a mid-infrared
laser, the

quantum cascade laser.

The beam comes out through
a lens here.

The beam is directed by these
mirrors through this hole,

into the sampling cell,
where the beam

passes multiple times.

The exit beam again goes
through the hole.

And it's focused right
onto the detector.

We can see signals from nitrous
oxide, acetylene, and

carbon monoxide.

Many kinds of human activities
lead to the emissions of both

greenhouse gases and
air pollutants.

We need to understand their
impacts on both climate and

air quality.

We took our sensors into the
field, to a location between

Washington, DC and Baltimore:
Beltsville, Maryland, where

there are both agricultural
and urban activities.

So we compared our measurements
with the typical

method, collaborating with the
scientists from the USDA.

We were really surprised that it
worked the first time out.

Normally, when you're working
with sensors, the first time

it doesn't work out
right away.

This is exactly the engineering

You know you have a problem to
solve, but you don't know

exactly how.

So you try something.

And even if it fails, you can
usually see what it takes to

make it work.

We hope that one day our
sensors will be able to

measure trace gases on a large
scale, so that people

everywhere can understand
their effects on the



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