Light oscillations become visible

August 28, 2004

The human eye can detect changes in the intensity of light, not however the wavelength because light oscillates too fast (approximately 1000 trillion times per second). An international collaboration led by Ferenc Krausz and made up of researchers from the Vienna University of Technology, the Max-Planck-Institute for Quantum Optics and the University of Bielefeld have recently succeeded in developing a technique which can measure the instantaneous electric field of red light (quarter period ~ 620 attoseconds) and record its variation with a resolution of 100 attoseconds (Science, August 27, 2004). The experiment of the Austrian-German team allowed the first direct visualization of the electric field of visible light and constitutes the fastest measurement to date.

It has been known since the famous experiments of Heinrich Hertz near the end of the 19th century that light is a wave consisting of electric and magnetic fields, just as radio waves and microwaves. The only difference is in the number of times these fields change their direction in a second. In radio and microwaves this happens typically millions to trillions times per second. The field variation in these waves can be readily detected by turning it into electric current and displaying the variation of this current in electronic instruments called oscilloscopes.

Light oscillations become visible


Fig. 1: Energy shift (in units of eV) suffered by an attosecond electron probe set free at different instants (measured in units of fs) in an intense wave consisting of only a few cycles of red light.


In striking contrast, the electromagnetic field of visible light changes direction approx. one thousand trillion, i.e. 1 000 000 000 000 000, times per second, so that the instantaneous intensity of the light field varies from zero to maximum faster than a femtosecond (1 femtosecond being one thousandth of a trillionth of a second), some ten thousand times more rapidly than the resolution of the fastest electronic instruments available to date. Recording the field variation of visible light calls for an oscilloscope that exhibits a temporal resolution of several hundred attoseconds (1 attosecond being a thousandth of a femtosecond). The researchers recently succeeded in developing a technique which can measure the instantaneous electric field of red light (quarter period ~ 620 attoseconds) and record its variation with a resolution of 100 attoseconds.

The key to this measurement was the generation of single 250-attosecond extreme ultraviolet pulses, a feat achieved by the same collaboration a few months ago (Nature, February 26, 2004). The attosecond extreme ultraviolet pulse knocks electrons free from atoms to probe the electric field of a wave consisting of only a few cycles of red laser light. The electric field of red light accelerated or decelerated the electrons set free with respect to the light wave with a 100-attosecond timing precision. The change in the electrons’ energy (shown in units of electron volts, eV, in Fig. 1), measured as a function of delay (shown in units of femtoseconds, fs, in Fig. 1) between the attosecond pulse and the laser light wave clearly exhibits the build-up and disappearance of the laser pulse within a few femtoseconds as well as oscillations with a period of the 2.5-fs wave cycle of 750-nm (red) light. The measured energy change directly yields the variation of the instantaneous strength and direction of the electric field of the few-cycle light wave (Fig. 2).

fig2


Fig. 2: Build-up and disappearance of the electric field in the 4.3-fs pulse of red light (wavelength ~ 750nm), as recorded by the attosecond oscilloscope.


The red line in Fig. 2 depicts the electric field of a few-femtosecond flash of red light, as recorded by an apparatus that can be regarded as the first attosecond oscilloscope. The new technique permits direct and accurate measurement of ultrabroad-band light pulses (made up of many different colours), and thereby opens the door to the reproducible synthesis of ultrashort flashes of light with arbitrary waveform for a number of applications including the development of molecular electronics and X-ray lasers.

Source: Max-Planck-Institute of Quantum Optics

Explore further: In a first, tiny diamond anvils trigger chemical reactions by squeezing

Related Stories

Some black holes erase your past

February 21, 2018

In the real world, your past uniquely determines your future. If a physicist knows how the universe starts out, she can calculate its future for all time and all space.

Scientists test world's first solar fuels reactor for night

February 21, 2018

International solar thermal energy researchers have successfully tested CONTISOL, a solar reactor that runs on air, able to make any solar fuel like hydrogen and to run day or night - because it uses concentrated solar power ...

Physicists contribute to dark matter detector success

February 21, 2018

In researchers' quest for evidence of dark matter, physicist Andrea Pocar of the University of Massachusetts Amherst and his students have played an important role in designing and building a key part of the argon-based DarkSide-50 ...

Reaching new heights in laser-accelerated ion energy

February 20, 2018

A laser-driven ion acceleration scheme, developed in research led at the University of Strathclyde, could lead to compact ion sources for established and innovative applications in science, medicine and industry.

Recommended for you

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...

Urban heat island effects depend on a city's layout

February 22, 2018

The arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide ...

A statistical look at the probability of future major wars

February 22, 2018

Aaron Clauset, an assistant professor and computer scientist at the University of Colorado, has taken a calculating look at the likelihood of a major war breaking out in the near future. In an article published on the open ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.