The present chapter serves as a brief introduction to semiconductor light sources mainly laser diodes and light emitting diodes, and the basic physical properties of their semiconductor materials. The chapter also discusses the main reasons for semiconductor light sources being attractive for biomedical applications which range from patient diagnostics imaging to direct treatment such as using photodynamic therapy. It is expected that this specific application area will grow significantly in the future, and that it will be an increasingly important physical properties part of the semiconductor industry.

We have attempted an overview of fast-pulsating lasers (gain-switched, Q-switched and mode-locked) in various biomedical applications. By necessity, the accents in the chapter have been to an extent coloured by our research experience and interests; apologies are extended to those authors whose work may have been omitted. Different properties of a laser system are important for different applications (e.g., high instantaneous and average power for multiphoton spectroscopy vs. spectral tuning range for OCT), but all the designs above benefit from the properties of semiconductor lasers such as chip compactness, ease of pumping, and high gain per unit length. The use of nanostructures, particularly QDs, has been shown to open new exciting opportunities.

In this chapter, we provide a brief review of the optical and electrical pumped GaN based vertical-cavity surface-emitting lasers from the fabrication technology to output characteristics analysis. Three types of vertical cavity surface-emitting laser (VCSEL) structures are discussed in the following paragraph including their pros and cons among design and process difficulties. First type is fully epitaxial VCSEL structure, second one is the hybrid microcavity consists of a bottom epitaxial distributed Bragg reflector (DBR) and a top dielectric DBR, and third one is vertical resonator composes dielectric top and bottom DBR. We also present several examples of GaN-based VCSELs achieve laser action under optical and electrical pumping at room temperature.

In this chapter, we will give a short introduction to nonlinear frequency conversion with second-order nonlinear optics to provide the basic background to the topic and highlight the important parameters to consider when designing a light source based on frequency conversion. In the following section, the different commonly used implementations of nonlinear frequency conversion will be introduced and some examples of demonstrated laser sources will be given. Finally, we will provide an outlook for the development of frequency converted diode laser light sources and briefly discuss some of the applications.

The intention with this chapter is to briefly review the capabilities made possible in the field of biomedical diagnostics and treatment by employing upconverting nanoparticles (UCNPs), as well as the importance of appropriate light sources for such applications. The field of UCNPs in biomedicine has grown rapidly the last decade, since they first were made sufficiently small and bright to be of real interest for biomedical applications. This research has been reviewed previously, while this chapter will focus on recent advances in the use of UCNPs for preclinical applications and diagnostic assays using laser diode excitation.

During the 2000's and 2010's Raman spectroscopy has proved its potential to be used for chemical fingerprinting of biological materials. This has enabled this technique to be translated as a novel diagnostic tool for disease diagnosis with high sensitivity and specificity. Raman scattering, being a weak process, relies greatly on the power and spectral quality of the excitation source for its effectiveness. Advent of relatively high power, frequency stabilized semiconductor lasers which has relatively small form factor when compared to its gas laser counterparts enabled developing portable Raman systems for clinical diagnostics.

In this chapter, we will provide a brief explanation of the principle of optical coherence tomography (OCT) imaging and highlight the influence of the light source properties. We will discuss the application of semiconductor lasers in specialized light sources for OCT, namely, in broadband light sources and in broadband wavelength-swept light sources. We will conclude with an outlook on the continuing development of light source technologies for OCT.