Assignment 1 | Laser Physics | SSP 4713

Name : Nadhrah bt Murad

Program : 4 SSZ

I/C No. : 910723-06-5100

Matric No. : AS 100097

Lecturer : Dr Raja Kamaruzaman bin Raja Ibrahim

Questions :

Choose one type of laser. Discuss :-

1. How laser can be produced 2. Active medium used3. Energy level system4. Pumping source5. Laser system6. Efficiency

Answers :

Type of laser : Liquid laser ( Dye laser )

No. Questions Answers

1. How laser can be produced The light from a laser contains exactly one color or wavelength rather than a lot of different wavelengths. Scientists say that laser light is monochromatic, meaning of one color. All the wavelengths are in phase. That is, they are all "waving" together, like a well-timed audience "wave" at a football game.

All the wave crests (high points) and troughs (low points) are lined up. Scientists say the laser light is coherent. While light waves from ordinary sources (such as flashlights, light bulbs, or the Sun) spread out in all directions. Laser light waves all travel in the same direction, exactly parallel to one another. This means that laser light beams are very narrow and can be concentrated on one tiny spot.

Scientists say the laser light is collimated. Because the laser light is monochromatic, coherent, and collimated, all of its energy is focused to produce a small point of intense power. This focused power makes laser light useful for cutting and welding. It also makes it possible to control laser light very precisely and make it do all kinds of useful things.

2. Active medium used In dye laser the liquid material called dye (for example rhodamine B, sodium fluoresein and rhodamie 6G) uses as an active medium, which causes to produce laser light.

3. Energy level system

The S0 to S1 transition covers a broad range of frequencies due to the rotational-vibrational energy levels. Once excited to the S1 state, these molecules can de-excite to the lowest vibrational level of S1 in a transition which takes a pico-second. This non-radiative decay is referred to as internal conversion. Transitions from this lowest vibrational level of S1 to the vibrational levels of S0 can occur spontaneously. A further possibility is that molecules nonradiatively move from S1 to T1, or S2 to T2. Spontaneous emission occur from T1 to S0.

4. Pumping source Nd-YAG laser is used to excite the dye. Their setup looked like:

5. Laser system The pumping process works like this:

1. Rapid excitation of a vibrational-rotational level of S1 2. Internal conversion to the lowest vibrational level of S1

3. Laser emission to the vibrational-rotational levels of S0 sufficiently far above the ground state that their populations are low (Davis 251).

The system needs the S1 state to be heavily populated because of the broad fluorescence spectrum. Furthermore, intersystem crossing populates T1 and absorption can occur from the same wavelengths as emitted in the fluorescence. This loss must be minimized and is done so by adding substances such as oxygen or detergents to the dye. This can further be done by using a dye solution in which intersystem crossing is unlikely to occur. Using the Nd-YAG laser, however, the transfer to the triplet state can be ignored because of the short laser pulses. When the pump intensity is sufficient to achieve an upper level population density, the lower level is scarcely populated.

6. Efficiency The output power of dye lasers can be considered to start from 1 watt with no theoretical upward limit. The output beam diameter is typically 0.5mm and the beam divergence is from 0.8 to 2 milli radians. The conversion efficiency of the light from the pumping source to an output from the dye laser is relatively high approximately 25%.