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Frequently Asked Questions


Glossary

Streak Camera

A streak camera is a device to measure the time dependence of very fast and very weak optical signals. Its main component is a vacuum electron tube which integrates:

A 3-dimension image is obtained for a every optical pulse incident on the photocathode. The intensity of the signal collected on the screen corresponds to the intensity of the incident signal, the horizontal and vertical axis correspond respectively to the time and the position along the cathode.

In some applications, one can replace the spatial dimension by a spectral dimension by placing a spectrometer in front of the streak camera.

Lasers

CPA Lasers
Laser systems using the Chirped Pulse Amplification (CPA) technique to amplify femtosecond pulses to Terawatt level.

Chirped Pulse Amplification

The typical characteristics of this type of lasers are given in the following table:

Repetition Rate
(pulses / second)
<0.03 10 1000
Energy per pulse 0.5-10 J 50-500 mJ 0.1-1 mJ
pulse duration 300 fs - 1 ps 100-500 fs 50-200 fs
Peak Power 0.5- 50 TW 0.1-5 TW 0.5-20 GW

Time Units

Short pulse
In this research field, "short" corresponds to time a duration typically of the order of 1 picosecond or shorter.

Picosecond
1 picosecond (ps) =10-12 second, or 1 millionth of 1 millionth of a second.

1 picosecond (ps) = 1000 femtosecond (fs)

In 1 picosecond, light travelling at 300 000 km/s, travels only 0.3 mm.

Subpicosecond
A time duration shorter than 1 picosecond and typically longer than 100 femtosecond.

Femtosecond
1 femtosecond (fs) = 10-15 second, or 1 millionth of 1 billionth of a second.

Other Units

Energy
Energy is measured in Joules.

1 Joule (J) = 1000 millijoules (mJ)

Power
Power is measured in Watts which corresponds to 1 Joule per second.

1 Terawatt (TW) = 1000 Gigawatt (GW) =1012 Watts

Intensity
Intensity of light is measured in W/cm2. When focussed on a target, a femtosecond laser pulse can produce an intensity up to 1019 W/cm2. As a comparison, the intensity of sunlight received on earth is about 0.1 W/cm2.