**3. Properties of laser**

The distinctive properties of laser are coherence, highly monochromatic, intensive radiance and directionality. These optical properties can be quantified for analyzing the laser properties.

## **3.1 Coherence**

The relationship between magnetic and electronic components of electromagnetic wave refers to coherence property. The light beam is said to be coherent when these components are properly aligned as shown in **Figure 4**. There are two terms of coherence for a laser as spatial coherence and temporal coherence. Coherence is said to be spatial when the correlation of phases happens at different points in a space at a single point of time whereas in temporal coherence, correlation happens at single point in a space over a time period. **Figure 5** shows the concept of coherence. Temporal coherence can be quantified through two important measures such as coherence length and time. This property can be improved by run the laser in single longitudinal and transverse mode.

#### **3.2 Monochromatic**

It is the most important property of laser and it can be measured by spectral line width. When the range of emitted frequencies is small by a light source, it is said to be high monochromatic. Laser beam normally have very few or single spectral lines with highly narrow widths as shown in **Figure 6**. Monochromaticity is most important because wide range of applications depends on this property such as interferometry, velocimetry, holography, separation of isotope and communications which require laser beam content. But this property is a not decisive factor for machining.

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**Figure 7.**

*Comparison of radiation from normal light bulb and a laser beam.*

*Laser Machining*

**Figure 5.**

**Figure 6.** *Monochromaticity.*

*DOI: http://dx.doi.org/10.5772/intechopen.93779*

*Schematic of spatially and temporally (a) coherent light and (b) incoherent light.*

Directionality is a property by which a light beam bends after passing sharp corners of objects. Diffraction or scattering of light at sharp edges increase the distance

**3.3 Low-diffraction or collimation**

**Figure 4.** *Components of electromagnetic wave.*
