Laser : Fundamentals

Problem

Please answer the following questions:

Question

A helium-neon laser emitting at 633 nm makes a spot with a radius equal to 100 mm at 1/e2 at a distance of 500 m from the laser. What is the radius of the beam at the waist (considering the waist and the laser are in the same plane)?

Solution

Question

A ring laser cavity is composed of 4 identical mirrors with a reflection coefficient equal to 0.99. Determine the value of the gain needed in the amplifying medium to obtain laser oscillation.

Solution

Question

Calculate the gap in frequency between two longitudinal modes in a linear cavity whose optic length, L, =300 mm.

Solution

Question

What is the rate of repetition of the pulses emitted by a mode-locked laser? The optic length of the cavity, L, is 1 m.

Solution

Question

A mode-locked laser emits an average power P equal to 1 W. The rate of repetition of the pulses from this laser is equal to 100 MHz. Calculate the energy of each pulse.

Solution

Question

Consider a lower energy level situated 200 cm-1 from the ground state. There are no other energy levels nearby. Determine the fraction of the population found in this level compared to the ground state population at a temperature of 300 K.

Boltzmann's constant is equal to 1.38.10-23JK-1

The conversion from cm-1 to joules is given by: , where h is Planck's constant (6.62 10-34Js) and c is the speed of light in a vacuum (3.108ms-1)

Solution

Question

Consider an optical pump at 940 nm for a Yb:YAG crystal placed in a laser cavity. The wavelength of ytterbium is 1030 nm. If all the photons emitted by the pump are absorbed by the crystal and used for the lasing process, calculate the maximum power output. The pump power is 1 W.

Solution

Question

The amplifying medium of a helium-neon laser has an amplification spectral band equal to at 633 nm. For simplicity, the spectral profile is assumed to be rectangular. The linear cavity is 30 cm long. Calculate the number of longitudinal modes that can oscillate in this cavity.

Solution

Question

CO2 has a bandwidth equal to at . For simplicity, the spectral profile is assumed to be rectangular. The length of the cavity is equal to 1 m.

1. Calculate the number of longitudinal modes that can oscillate in this cavity.

2. At what distance must the cavity mirror be placed so that at least one of the modes falls in the amplification band?

Solution

Question

A Q-switched laser emits pulses of 10µJ of duration 1 ns. The repetition rate of the pulses is equal to 10 kHz.

1. Calculate the peak power of the pulses.

2. Calculate the average output power of the laser.

Solution

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