Laser microtome
Encyclopedia
The laser microtome is an instrument used for non-contact sectioning of biological tissues or materials. It was developed by the Rowiak GmbH, a spin-off of the Laser Centre Hannover.
In contrast to mechanically working microtome
s, the laser
microtome does not require sample preparation techniques such as freezing, dehydration or embedding. It has the ability to slice tissue in its native state. Depending on the material being processed, slice thicknesses of 10 to 100 µm are feasible.
in the near-infrared range. Within this wavelength
range, the laser is able to penetrate the tissue up to a certain depth without causing thermal damage. By tight focussing the laser radiation, intensities over 1 TW
/cm2 (1 TW = 1012 watts) arise inside the laser focus
. These extreme intensities induce nonlinear effects and optical breakdown
occurs. This causes the disruption of the material, limited to the focal point. The process is known as photodisruption.
Due to the ultra short pulse
duration of only a few femtosecond
s (1 fs
= 10−15 seconds) there is only very low energy
of a few nanojoule
s (1 nJ
= 10−9 joules) per laser pulse deposits into the tissue. This limits the interaction range to diameters below one micrometer (1 μm = 10−6 meters). Out of this range there is no thermal damage.
Moved by a fast scanner, the laser beam writes a cutting plane into the sample. A positioning unit moves the sample simultaneously, so that the sample can be processed within a short time.
In contrast to mechanically working microtome
Microtome
A microtome is a sectioning instrument that allows for the cutting of extremely thin slices of material, known as sections. Microtomes are an important device in microscopy preparation, allowing for the preparation of samples for observation under transmitted light or electron radiation...
s, the laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
microtome does not require sample preparation techniques such as freezing, dehydration or embedding. It has the ability to slice tissue in its native state. Depending on the material being processed, slice thicknesses of 10 to 100 µm are feasible.
Principle
The cutting process is performed by a femtosecond laser, emitting radiationRadiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
in the near-infrared range. Within this wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
range, the laser is able to penetrate the tissue up to a certain depth without causing thermal damage. By tight focussing the laser radiation, intensities over 1 TW
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
/cm2 (1 TW = 1012 watts) arise inside the laser focus
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
. These extreme intensities induce nonlinear effects and optical breakdown
Narrow bipolar pulse
Narrow bipolar pulses are high-energy, high-altitude, intra-cloud electrical discharges associated with thunderstorms. NBP are similar to other forms of lightning such as return strokes and K-changes, but produce an optical emission of at least an order of magnitude smaller...
occurs. This causes the disruption of the material, limited to the focal point. The process is known as photodisruption.
Due to the ultra short pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
duration of only a few femtosecond
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s (1 fs
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
= 10−15 seconds) there is only very low energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
of a few nanojoule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
s (1 nJ
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
= 10−9 joules) per laser pulse deposits into the tissue. This limits the interaction range to diameters below one micrometer (1 μm = 10−6 meters). Out of this range there is no thermal damage.
Moved by a fast scanner, the laser beam writes a cutting plane into the sample. A positioning unit moves the sample simultaneously, so that the sample can be processed within a short time.