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

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. 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 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.
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

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.
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.
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.
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.
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.
Optromix offers high-performing lasers that are perfect for optical tweezers.

Atomic Cooling: scientific laser systems (laboratory laser, laser equipment)

Since 1976 scientists have been working on the idea of controlling (cooling, trapping) atoms with laser equipment. The atom trapped in the laboratory laser beam absorbs photons and becomes excited; photons can transmit their impulses to the atom. When atoms are de-excited, they reemit photons in random directions. As a result the atom experiences light pressure in the direction of the laser beam spread. Atoms get excited when the frequency drift is similar to the optical transition.
If an atomic gas is irradiated from each side with the laser frequency that is less than that of an atomic transition, the number of slow atoms grows leading to the temperature decrease.
The first atomic cooling experiment was conducted in the laser spectroscopy department of ISAN. Using the laboratory laser in dilatational cooling the transverse velocity is increased due to the growth of fluctuation atom impulses when laser light photons are absorbed and emitted. At some point of dilatational cooling its speed becomes comparable to that of the transverse one and for further dilatational cooling the transverse cooling of the beam has to be performed. First time it was done in the laboratory in 1984, and the record atom temperature of 0.003 K was reached. This temperature is close to the Doppler cooling.
All these experiments with scientific laser systems allowed decreasing the energy of neutral atoms to the levels when their space localization with electric, magnetic and laser fields became possible. This opened new opportunities for sharp decreasing the temperature of the atoms that were already cooled down.
ISAN was the first laboratory in the world to start experiments with controlling the atomic motion with laser equipment. Today there are dozens of laboratories around the world that work on this aspect using different scientific laser systems.
Different methods exist to cool neutral and excited particles (atoms, molecules and their ions), they are based on various dissipation processes. For example, electric cooling of excited particles is done through the collision of hot atoms and cold electron fluid. However, the most popular and effective way to cool neutral atoms (and localized ions as well) is the collision of those atoms and laser beam photons.

Holmium Advanced Laser Systems – a Better Choice for Q-switched Operations than Thulium Fiber Laser

20160204Trivalent rare earth ions Tm3+ and Ho3+ show extraordinary performance results for the high power continuous wave and pulsed laser operation in 2 µ wavelength range. Thulium fiber laser is, in general, better for CW operations, when holmium laser is preferred for pulsed and q-switched lasers operations because of its high gain. However, holmium can be excited around 1.9 µ for an efficient operation at 2.1 µ, or it needs to exploit some energy transfer from thulium or ytterbium.
Before recently, holmium laser products were created as co-doped systems, because there weren’t any laser diodes that could provide wavelength ranges for pumping Ho3+ ions. Mostly, thulium co-doping was used, because its ions cross relaxation process properties. Currently, the most potential option to reach the highest output powers is in-band pumping of Ho:YAG crystals. It is possible in 1.9 µ wavelength range.
There are a lot of different applications that need short laser pulses with high pulse energies or high CW powers at the 2.1 µ wavelength, which makes holmium lasers in high demand on the market. Mainly, holmium advanced laser systems are created using thulium crystals or fiber lasers for pumping. Moreover, 2.1 µ wavelength is eye safe, because the emission doesn’t reach the retina, which makes it not dangerous for eyes. This wavelength range makes holmium laser in demand for commercial use, especially for LIDAR systems, which operate similarly to radars. 2 µ wavelength allows one to absorb certain atmospheric gasses (e.g. H2O, CO2, N2O) to detect and to analyse them. One of the key advantages of this laser for LIDAR technology is the capability to detect specific lighter atmospheric gasses and molecules. It has a greater potential than thulium fiber laser in chemical and petroleum industries due to safety and quality control as well as in medicine and environmental research.
oreover, holmium laser is very promising in terms of medical applications. High water absorption allows performing extra precise surgeries; 2.1 µ emission coagulation effects minimize bleeding. Ho:YAG penetrates into a soft tissue at the depth of 300 µ. However, thulium fiber laser has its own advantages in performing surgical procedures. Holmium laser systems have a lot of potential and, definitely, require further developments and research. They can be applied in a lot of different industries for various purposes, including spectroscopy, sensing and surgery.

Utilizing Nd:YAG Q-switched Lasers in Solid-State Laser Technology

20160120Q-switching technique is usually utilized in solid-state laser technology to generate nanosecond high energy pulses. It creates short pulses through regulating cavity losses. Q factor (quality factor) is a definition of an oscillation damping strength measurement.
There are two types of q-switching: passive and active.
Active q-switching technique uses an electrically controlled modulator (acousto-optic or electro-optic). It is applied to control optical losses which are high initially, but in the process of switching they are lowered abruptly. Pump phase and the gain-medium upper-state lifetime should be roughly the same to avoid losing energy in spontaneous emissions. Energy loss through spontaneous emissions becomes significant when laser gain is high. However, it is not the biggest concern when it comes to bulk lasers. A bigger issue is parasitic lasing because of unwanted reflections or q-switch. To avert the lasing a modulator should have a high pump phase when performing power losses.
It is possible to design smaller mode area lasers when the energy per pulse and energy stored are lowered due to high pulse repetition rates (10 kHz, 100 kHz or more). However, high repetition rates create another issue – collecting enough laser gain even when stored energy is low, because when the gain is low pulses become longer. Even in case of high average powers it can still be problematic, because it may need bigger beam areas. That is why it is better to select a crystal providing a higher laser gain, for example, Nd:YVO4.
Passive q-switching technique uses a saturable absorber instead of an electrical modulator. There is a high optical loss when it is in the unsaturated state. To start the lasing a laser gain has to reduce that loss. When the emission increases, it saturates losses, and the laser power grows fast, which leads to the gain saturation.
It may give an impression that it is poor because of the absorption; however this is not the case. Just a little portion of energy is required for an absorber transparency, when the laser gain medium saturation energy is higher than the absorber energy. One of the most common crystals used in this case is Nd:YAG.
The pumping in a passive q-switched laser continues up to a moment when a pulse build up begins. This process begins when there is enough energy stored in the gain medium. The main difference between passive and active q-switching technique is that in case of a passive one the pumping power change does not affect the energy pulse, it will only effect the timing. In active q-switching technique both will be affected, the energy pulse and timing.

Thulium Fiber Laser for LIDAR and Gas Sensing Systems

20160110Ultra-short pulsed femto- and picosecond lasers are in high demand today. Thulium-doped lasers, definitely, stand out because of their capability to generate emissions in a wide range. Thulium Fiber Laser has unique qualities which make it perfect for a lot of different applications, namely, medicine, spectroscopy, laser ranging and micromachining of transparent materials, in particular, semiconductors and laser for LIDAR. Presently, they are the most effective sources of a single-mode emission with the wavelength in 2 µ range.
Thulium Fiber Laser water absorption properties are outstanding. The main constituent of any biological tissues is water, which is why strong water absorption quality of thulium laser allows significant heating of small areas. In other words, cutting biological tissues becomes extra precise. All of the above make Thulium Fiber Laser irreplaceable when it comes to performing surgical procedures.
Thulium lasers compared to traditional optimal cost-efficient laser systems that operate at shorter wavelengths have undeniable advantages when using for free space applications. It gives them a high commercial value, especially as laser for LIDAR and gas sensing systems, optical communication applications and pumping lasers for the mid infra-red spectrum.
Thulium doped lasers are released either in fiber or crystal host materials. Depending on the host material the wavelength range spreads from 1840 nm to 2100 nm. Thulium fiber can either be a q-switched laser or continuous wave laser, and both develop significantly a high average power. On the other hand, thulium doped crystals have a broad emission spectrum, which allows a large wavelength tuning range. Thulium doped crystals are of really good quality with a few imperfections and defects. YAG and YFL crystals reveal the best quality nowadays; however, they are not the best choices because of their thermal conductivity and emission cross section. There is definitely a room for improvement, and further research has to be done to enhance their performance.
Despite the fact that there are so many different applications in a lot of industries only few laser technology providers can deliver this type of laser at the moment. Currently, Optromix is developing its own thulium laser and will release it shortly for commercial use (e.g. laser for LIDAR).

Powerful laser equipment: Nd:YLF Laser or Nd:YAG Laser

20151119Nd:YLF laser active elements are made of yttrium lithium fluoride (YLiF4) crystal. YLF stands for Yttrium Lithium Fluoride. Usually neodymium-doped YLF crystal is used for YLF laser equipment; however, it can also be doped with rare earth elements, such as ytterbium (Yb), erbium (Er), thulium (Tm), holmium (Ho) or praseodymium (Pr).
Yttrium ions in YLF crystal may be substituted with laser-active rare earth ions, because of its similar size, without distorting the structure of crystal lattice. In neodymium-doped YLF crystal its (Nd3+) concentration is usually up to 1% of its total weight.
YLF crystal has a natural strong birefringence, which removes thermal polarization losses. Besides the emission wavelength and the gain of the Nd:YLF crystal waves are polarization-dependent, there is a stronger wave of 1047 nm and a weaker one of 1047 nm. It makes Nd:YLF crystal better for a less powerful laser equipment that require extra precision.
1053 nm wavelength matches the maximum for loop gain of phosphate laser glass, that contains neodymium ions, that is why Nd:YLF lasers are often used as a master oscillator and preamplifier for the subsequent stages of the neodymium phosphate glass amplifier.
Diode-pumping and lamp-pumping is possible for Nd:YLF laser. It has lower thermal conductivity in comparison with Nd:YAG laser, but its thermal distortions are weaker, which leads to a better beam quality and worse fracture resistance, hence it limits the output power in the laser equipment.

Nd:YAG is an Optimal Cost-Efficient Laser for Scientific Laser Systems

20151117YAG stands for yttrium aluminum garnet, which is a synthetic crystal. Nd:YAG is an artificial cubic garnet crystal. YAG crystals were created shortly after ruby laser discovery. They have high gain and other unique properties which make them universal for a lot of different applications. YAG crystals increase the stability of the source, its efficiency and lifespan, reduce size and power consumption.
There are certain limitations connected with the high gain and the safety of the operating fluence. Mode-lock property creates pulses of very different widths – nanosecond to picoseconds, which enables it to make wide-ranging peak power for various applications.
YAG laser is a solid state diode pumped laser, its beam is in mid infra-red range and its wavelength is 1064 nm. Nd:YAG is an outstanding solution for scientific laser systems because it can reach extremely high powers in a pulsed mode, which is used in the oscillators to produce series of very short pulses to perform research with femtosecond time resolution.
Nd:YAG laser may be used with a frequency doubler, in this case its wavelength is 532 nm and its output power is lower.
In terms of applications, yag laser systems are very versatile. It has been widely used in the military, for example, for rangefinding or for target designation.
On the other hand, as mentioned before its pulse width and high power, it is extremely useful for scientific purposes, or as a pumping source for other lasers.
Medicine is another field where Nd:YAG is frequently used, namely dermatology and ophthalmology. Commercial purposes include applications such as ablation, spectroscopy, marking, nondestructive testing and others. Moreover, it is an optimal cost-efficient laser.
Key feature of the YAG lasers is its resilience to different environmental conditions; hence it suits perfectly well for remote sensing, bathymetry, gated imaging illumination, atmospheric and ocean studies, etc.
Other lasers or nonphotonic techniques may be used for most of the applications mentioned above, for example, diode or CO2 lasers. Nd:YAG allows to perform a broad range of applications, because of its one-of-a-kind properties, and also, not many lasers have an ability to function efficiently with diode pumping and to switch between pulsed or CW mode.

Advanced laser systems, technology and equipment for LIDAR

LIDAR (light detection and ranging) is a laser technology used for optical remote sensing which allows one to analyze scattered light properties in order to obtain certain information about a distant object.
These advanced laser systems are often used, for example, to collect precise information about Earth surface and its characteristics. The sensor sends out a pulse of light to travel to an object, it reflects off the object and travels back. When the light clashes into an object, the sensor detects the reflected pulse. Then it measures the time necessary for the reflected pulse to return. The light pulse travels with the speed of light which is known and constant; hence, the time is easily converted into distance or as it is called – the range. The information on the position and angle of the laser equipment allows calculating exact coordinates of the object reflected.
LIDAR technology can be applied in a lot of different areas, from geographical mapping to robotics due to its high configuration capabilities and wavelengths.
There are different types of LIDARs: rangefinder, DIAL and Doppler.
Rangefinders measure a distance between a sensor and a solid object.
DIAL (differential absorption) measures chemical concentrations in the atmosphere (ozone, water vapor, pollution). It emits pulses with two different wavelengths which are set in a specific way, so that a molecule can absorb one of them, but the other can’t. This way the molecule concentration is deduced.
Doppler technique measures an object velocity. When a light pulse travels to a moving object, its wavelength changes a little, and it is called Doppler shift. When the object is moving away from the sensor, the reflected wavelength will be longer, and when the object is moving towards the sensor, the reflected wavelength will be shorter.