Comparison of laser crystals

This article mainly introduces the characteristics and applications of various common crystals, and compares them.


Form of Comparison of Crystals

Nd:YAG crystal

Nd:YAG crystals have the characteristics of good mechanical properties, high gain, good thermal properties and optical uniformity, and are widely used in scientific research, industry, military and other fields. The relatively small gain bandwidth of Nd:YAG crystal can achieve high gain efficiency and relatively low lasing threshold. Its excellent thermal and mechanical properties allow the growth of crystals with high optical quality and large diameters. Its appearance has made solid-state lasers vigorously developed and successfully commercialized. Nd:YAG crystals absorb at 808nm and typically emit light around the peak at 1064nm, but there are also transitions around 940nm, 1120nm, 1320nm and 1440nm.

In high-power CW lasers and solid-state lasers, as well as military lasers, Nd:YAG crystal is one of the main application materials. The current main applications are as follows:

  • Manufacture for engraving and etching various metals, plastics;
  • Medical – such as endoscopy, urology, neurosurgery, gynecology, dermatology, dental surgery and general surgery to treat various diseases such as cancer and liver disease, etc.;
  • rangefinders and lighting equipment;
  • For engineering applications such as resistance, trimming, drilling, etc.;
  • for process visualization technology;
  • For spectral analysis.

Nd:YVO4 crystal

The Nd:YVO4 crystal is uniaxial and only emits linearly polarized light, avoiding the influence of unnecessary birefringence on frequency doubling. It is very suitable as a medium for high repetition rate Q-switched lasers and low threshold CW lasers.

The absorption peak wavelength of Nd:YVO4 crystal is 808nm, and the emission is 914nm, 1064nm and 1342nm.

Advantages of Nd:YVO4 comparison:

Compared with Nd:YAG, the stimulated emission cross-section of Nd:YVO4 at 1064 nm is several times larger, and the stimulated emission cross-section at 1342 nm is more than twelve times larger than that of Nd:YAG. If a pulsed or continuous wave laser is to be constructed, Nd:YVO4 is a good medium in place of Nd:YAG.

The absorption coefficient of Nd:YVO4 is greater than that of Nd:YAG, and using the same 808 nm diodes, if Nd:YVO4 is used, these diodes can be used at lower power, increasing the life of the diodes.

Disadvantages of Nd:YVO4 compared to Nd:YAG:

The up-state lifetime of Nd:YVO 4 is about 2.5-3 times shorter than that of Nd:YAG. This means that it is difficult (sometimes even impossible) to obtain pulse energies as high as Nd:YAG during Q-switching

Applications: low and medium power lasers, machine vision, spectroscopy, medical lasers

Ti:Al2O3 crystal

Titanium sapphire (Ti:Al2O3) crystal has high stability and very long service life, and can be used in laser systems with a wavelength range of 600-1050 nm to realize femtosecond laser pulses. In June 1982, Peter Moulton constructed and invented the first titanium:sapphire-based laser at the MIT Lincoln Laboratory.

The absorption band of titanium:sapphire is centered at 490 nm, making it suitable for a variety of laser pumping light sources – argon-ion, frequency-doubled Nd:YAG and YLF, copper vapor lasers. With a fluorescence lifetime of 3.2 μm, short-pulse flash lamps can efficiently pump Ti:sapphire crystals in powerful laser systems.

Applications: Medical Laser Systems, LiDAR, Laser Spectroscopy.

Comments

Post a Comment

Popular posts from this blog

Application of Structured light projection

Structured light projection (SLP) is a non-contact optical metrology method which can measure to the micron scale. The technique involves projecting a known light irradiance pattern onto the surface under test, which then scatters the light creating a 3D image on the surface. The scattered light is recorded by one or more cameras and the scattered pattern is compared to the modeled projected pattern to determine the surface profile.  For a test surface to be measurable with the SLP technique, it must be a scattering surface over the spectrum of light that is projected on to it. Typically, visible light is used for a SLP device, as the light sources and projection mechanisms are more straightforward to achieve, although another wavelength can be used when necessary. Figure below demonstrates a projected fringe pattern that was captured by a camera, and the corresponding surface that was calculated. Surface height accuracy The surface height features that are measurable by the SLP te...
Read more

What is Reflective Coatings?

Image
A very important coating is a reflective version that produces mirrors, coated on the front or back transparent optical material or on the front surface of metallic substrates. This kind of coating reflects a high amount of energy (light in the visible range), which is important for its intended use. As the AR coatings, reflective coatings are also designed for different regions of the spectrum. Aluminum is the most common metallic coating material. Table below shows different kinds of coating materials and the percentage of reflection in different wavelengths. The other type of optical coating used for reflection purposes is the dielectric coating, which uses thin layers of transparent dielectric materials with different refractive indices (e.g., magnesium fluoride or calcium fluoride) and various metal oxides that are deposited onto the optical substrate.
Read more

Applications of Machine vision

Image
Machine vision is a very wide area, encompassing practically any system that uses a camera and processing unit to perform an inspection or measurement task. The hardware is typically off-the-shelf components (e.g., telecentric camera) with potentially custom software written to control the devices. The systems help automate processes, speed up manufacturing, and increase yield by replacing a task done by a human that can fatigue and make mistakes. Surface defect inspection Machine vision systems have become widely used in production environments for their automation of an operator’s manual inspection process. Such systems can be used to quantify the geometric dimensions of mechanical features [12]. More recently, machine vision has been applied to the assessment of optical surface quality (scratch dig), typically a task performed by an expert operator. The automation of surface quality inspection affords a repeatable and standardized assessment at the cost of single-purpose systems...
Read more