High-technology laser systems: gas laser holography methods in medicine

gas laser holography

Applications of Holography in Ophthalmology

Holography methods require high-technology laser systems and, just like interpherometery, are often used in ophthalmology. Certain researches have high potential in this sphere: three-dimension image of the eye and its parts, studying optical eye features and measuring internal eye structures with the high resolution.

Imaging Internal Eye Structures

Most of the research today is about creating an image of the internal volume of the eye, and developing an optical scheme to make a wide angle holographic photo. One of the experiments used laser with 632 nm and 589 nm to create a hologram of an eye of animal. Cross-polarization was used to avoid parasite and interfering beams from mirror reflections of an eye and a lens. The images of the blood vessels have been made, however, the main purpose of the holography – three-dimensional image of the objects – hasn’t been achieved. It happened because the resolution wasn’t high enough.

High-technology Laser Systems for Fundus Imaging

High-technology laser system with double-beam is used to obtain the fundus hologram, the regular fundus camera has its xenon light source replaced with an argon gas laser, and its emission is used to illuminate the eye fundus and create a bearing beam. The studies show that the gas laser holography methods have relatively low resolution and low contract images, which can be explained by the speckle pattern that affects the general image.

Advantages and Methods of Holography

In general, holography with gas laser is useful to localize intraocular foreign body and to study different processes such as tumors, edemas, amotio, etc. Using single-pass holographic registration allows achieving a better quality of three-dimension images, fluorangiography is a primary method, a luminescence colourant is inserted in blood, and it helps to register the images of fundus.
There is no doubt that holography method has a great potential in the area of biomedical diagnostics, in particular, in ophthalmology, however, it presents certain challenges that prevent animal experiments from showing excellent results. Further optimization of high-technology laser systems parameters need to be done.

High-performing laser: Single-frequency laser system for optical tweezers

optical tweezers

Principles of Optical Tweezers

The principle of the optical tweezers is based on the fact that light beam has a pulse and when it its direction is changing it creates power.

Concept of Pulse in Mechanics

The concept of a pulse comes from mechanics, where the body mass multiplied to its speed stand for the pulse. Speed is a vector that describes the magnitude and the direction. Hence, object motion happens under the influence of power, and the direction of the speed is connected to the shift of the power direction.

Light Interaction with Particles

When a photon is projected on a non-transparent surface, then the pulse is just the light pressuring on this surface. However, when pointing the high-performing laser on the transparent particle, the light beam is diffracted – the direction of the light vector and as a result of the photons is changing. By analogy with the mechanics it is fair to say that the power shift will affect the particle in a way that it will move towards the highest insensitivity of the laser beam.

Gaussian Beam Trapping

Insensitivity of the high-performing laser beam is the highest at the core and fades on the edges. The law of the insensitivity shift corresponds to the Gaussian distribution. That is why the particle stays at the core of the beam, and when the beam is focused it is “sucked in” by the beam and becomes “trapped”. This kind of three-dimension trap needs power of several mV.

Manipulating Particles with Optical Tweezers

By moving the focus it is possible to move the particles, creating different structures with them. Using the optical tweezers the scientists can trap a chromosome and then cut it for further research. Single-frequency laser system with 1064 nm wavelength is a good solution for trapping, and for cutting a green laser with 532 nm wavelength. Optical tweezers is the best tool for these kinds of manipulations; however, it has certain weaknesses.
First of all, the more the beam is focused the faster it radiates. This means that the power holding the particle fades very fast the further away it is from the trapping zone, and at the distance of several dozens of microns from the focus the power is insufficient to trap it again. Single beam trap is only useful to trap a single particle located in the focus area.
Second of all, laser beam changes after it reaches the object because of the diffraction, reflection or absorption. This also limits the distance of optical tweezers.
The more the beam radiates the harder it is to focus the optical system, and it is impossible to obtain the perfect parallel beam because of the diffraction. However, there is a type of light beams that are free from diffraction, they are called Bessel’s beams.
Regular Gauss beams are converted into Bessel beams with so called axion conical lens that focuses the High power single-frequency laser beam not into a dot, but into a line. Optical tweezers that use Bessel’s beam can trap particles located on a distance of 3 mm from each other. Single-frequency laser system with 1064 nm wavelength was used.
Optical tweezers allow measuring different mechanical properties of the DNA molecules. It is currently used to transplant genes into cells, and also for invitro fertilization.