Difference between pulsed laser source and Monochromatic laser source:

1. Pulsed laser: 在一段时间内，断断续续的产生脉冲一样的激光。对于Continuous wave(CW) laser ，就是产生强度不变的、连续的激光，如下如所示。
2. Monochromatic laser source: all of the light produced by the laser is of a single wavelength.一般的激光特性就是。

拓展激光的知识：

A laser generates a beam of very intense light. The major difference between laser light and light generated by white light sources (such as a light bulb) is that laser light is monochromatic, directional and coherent. Monochromatic means that all of the light produced by the laser is of a single wavelength. White light is a combination of all visible wavelengths (400 - 700 nm). Directional means that the beam of light has very low divergence. Light from a conventional sources, such as a light bulb diverges, spreading in all directions, as illustrated in Figure 2. The intensity may be large at the source, but it decreases rapidly as an observer moves away from the source.

Figure 2. Divergence of Conventional Light Source

In contrast, the output of a laser, as shown in Figure 3, has a very small divergence and can maintain high beam intensities over long ranges. Thus, relatively low power lasers are able to project more energy at a single wavelength within a narrow beam than can be obtained from much more powerful conventional light sources.

Figure 3. Divergence of Laser Source

Coherent means that the waves of light are in phase with each other. A light bulb produces many wavelengths, making it incoherent.

Figure 4. Incoherent light bulb vs. coherent laser

多纵模激光和单纵模激光的优缺点：

· 多纵模功率更高

· 单纵模功率一般更低，有更低的带宽（bandwidth）,更难制造。

There are advantages and disadvantages to both multi-longitudinal mode and single longitudinal mode diode lasers. For example, multi-longitudinal mode diode lasers are generally more straightforward and more cost effective to manufacture. Additionally, the larger number of modes typically allows for much higher power to be generated by the device. Single longitudinal mode diode lasers though have a much narrower bandwidth which makes them more desirable for applications where precise knowledge of the wavelength is required. But as a result, these diode lasers are typically much lower power and more challenging to manufacture.

激光是一种单色光，它的颜色取决于发出激光的活性物质所产生的波长

参考：

LASER DIODE FUNDAMENTALS: UNDERSTANDING LONGITUDINAL MODES

LASER SELECTION GUIDE

Section 1: Laser Fundamentals

Pulsed vs. Continuous Laser: Why should we care?