Studying Tunability of Some NIR Semiconductor Lasers by External Cavity Setup

Abstract

In the middle of the 20th century, finding the fact that a p-n junction can be used for generating coherence light led to a great revolution in laser industry and as a consequence in the related fields [1]. The smaller dimension and very lower weight compared to other types of lasers, as well as low power operation, desired efficiency, low price and good tunability range were the main advantage that made them a remarkable field of research. Along with the development of the sciences of physics, chemistry and electronics, the technology of this type of lasers has also improved. Developments in related fields such as deposition, power supplies and optical design led this type of lasers to become efficient and single mode lasers. This type of lasers can be used for various applications such as laser spectroscopy experiments, the telecommunications industry, a source for pumping other lasers, measuring and manipulating the quantum state of atoms, laser cooling and generation of terahertz radiation [2-9]. Nowadays, using lasers with varying wavelengths is an interesting field of research [10]; therefore, lasers will turn more applicable when their wavelengths can be tuned. There are a number of tuning mechanisms; one of them is using an external cavity as a feedback section. The principle of laser wavelength tuning by use of external feedback typically includes a wavelength-selective device positioned in the optical path of the laser beam that feeds a narrow part of the laser emission spectrum back into the laser cavity. There is another type of external-cavity laser that uses a resonator based on an optical fiber rather than on free-space optics. Tunable external cavity diode lasers (ECDLs) have been broadly developed. They have different applications in various fields of science. [11]. Tunable external cavity diode lasers (ECDLs) usually use a diffraction grating as the wavelength-selective element in the external resonator. In ECDLSs, the first-order of diffraction of the grating provides optical feedback to the laser diode chip. In this case a diode chip is required with a bandgap producing sufficient gain at the desired wavelength. The typical laser diode will have gain over several nanometers. ECDLs will often simultaneously support two or more closely-spaced longitudinal cavity modes with the total output power split between modes such that the effective power is substantially reduced. ECDLs have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs [8, 9]. The aim of this paper is to study tunability of three near-infrared semiconductor lasers with center wavelengths from 800 nm to 1000 nm in two different configurations (wavelength dependent and wavelength independent beam direction setup).