Streak camera
Encyclopedia
A streak camera is an instrument for measuring the variation in a pulse of light's
intensity
with time. They are used to measure the pulse duration of some ultrafast laser systems, and for applications such as time-resolved spectroscopy
and LIDAR
.
A streak camera operates by transforming the temporal profile of a light pulse into a spatial profile on a detector, by causing a time-varying deflection of the light across the width of the detector. In particular, a light pulse enters the instrument through a narrow slit along one direction. It is then deflected in the perpendicular direction so that photons that arrive first hit the detector at a different position compared to photons that arrive later.
The resulting image forms a "streak" of light, from which the duration, and other temporal properties, of the light pulse can be inferred. Usually, in order to record periodic phenomena, a streak camera needs to be triggered accordingly, similarly to an oscilloscope
.
Mechanical streak cameras use a rotating mirror
or moving slit system to deflect the light beam. They are limited in their maximum scan speed and thus temporal resolution.
Optoelectronic
streak cameras work by directing the light onto a photocathode
, which when hit by photons produces electron
s via the photoelectric effect
. The electrons are accelerated in a cathode ray tube
and pass through an electric field
produced by a pair of plates, which deflects the electrons sideways. By modulating the electric potential
between the plates, the electric field is quickly changed to give a time-varying deflection of the electrons, sweeping the electrons across a phosphor
screen at the end of the tube. A linear detector, such as a charge-coupled device
(CCD) array is used to measure the streak pattern on the screen, and thus the temporal profile of the light pulse.
The time-resolution of the best optoelectronic streak cameras is around 100 femtoseconds . Measurement of pulses shorter than this duration requires other techniques such as optical autocorrelation
and frequency-resolved optical gating
(FROG).
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
intensity
Intensity (physics)
In physics, intensity is a measure of the energy flux, averaged over the period of the wave. The word "intensity" here is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech...
with time. They are used to measure the pulse duration of some ultrafast laser systems, and for applications such as time-resolved spectroscopy
Time-resolved spectroscopy
In physics and physical chemistry, time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Most often, processes are studied that occur after illumination of a material, but in principle, the technique can be applied to...
and LIDAR
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...
.
A streak camera operates by transforming the temporal profile of a light pulse into a spatial profile on a detector, by causing a time-varying deflection of the light across the width of the detector. In particular, a light pulse enters the instrument through a narrow slit along one direction. It is then deflected in the perpendicular direction so that photons that arrive first hit the detector at a different position compared to photons that arrive later.
The resulting image forms a "streak" of light, from which the duration, and other temporal properties, of the light pulse can be inferred. Usually, in order to record periodic phenomena, a streak camera needs to be triggered accordingly, similarly to an oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
.
Mechanical streak cameras use a rotating mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
or moving slit system to deflect the light beam. They are limited in their maximum scan speed and thus temporal resolution.
Optoelectronic
Optoelectronics
Optoelectronics is the study and application of electronic devices that source, detect and control light, usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light...
streak cameras work by directing the light onto a photocathode
Photocathode
A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...
, which when hit by photons produces electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s via the photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...
. The electrons are accelerated in a cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
and pass through an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
produced by a pair of plates, which deflects the electrons sideways. By modulating the electric potential
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
between the plates, the electric field is quickly changed to give a time-varying deflection of the electrons, sweeping the electrons across a phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
screen at the end of the tube. A linear detector, such as a charge-coupled device
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
(CCD) array is used to measure the streak pattern on the screen, and thus the temporal profile of the light pulse.
The time-resolution of the best optoelectronic streak cameras is around 100 femtoseconds . Measurement of pulses shorter than this duration requires other techniques such as optical autocorrelation
Optical autocorrelation
In optics, various autocorrelation functions can be experimentally realized. The field autocorrelation may be used to calculate the spectrum of a source of light, while the intensity autocorrelation and the interferometric autocorrelation are commonly used to estimate the duration of ultrashort...
and frequency-resolved optical gating
Frequency-resolved optical gating
In optics, frequency-resolved optical gating is a derivative of autocorrelation, but is far superior in its ability to measure ultrafast optical pulse shapes...
(FROG).