Excerpt from HMP 7 Chapter 8
Lasers: Current Trends
The majority of holographers once used red sensitive emulsions and Helium-Neon lasers. As the industry grew, new recording materials were utilized and commercial production required more powerful and more versatile CW lasers. Argon Ion, Krypton, HeCd and mixed gas lasers became standard equipment in the studio and in the factory. Diode Pumped Solid State lasers have recently been integrated into the manufacturing process.
This chapter first examines the "holographer-friendly" features that define the latest generation of ion lasers. It then introduces DPSS laser technology, including its advantages and current limitations. An overview of some of the lasers currently available from four of the world’s major laser manufacturers follows. The chapter concludes by discussing alternative sources for laser equipment.
Ion Lasers Improve; Solid State Diode Pumped Lasers Introduced
Until recently, successfully performing holography in most R&D or production applications usually required the use of an ion laser. The ion laser, in turn, required hands-on operator attention to maintain optimum alignment and achieve single-frequency operation. Fortunately, recent developments in laser technology have eliminated both these requirements. Specifically, ion lasers have undergone significant maturation in terms of ease of use and implementation, resulting in true "hands-free" operation, even for applications as demanding as holography.The first argon ion laser was made in 1964. Ion lasers opened the door to practical holography and have dominated this application because of their low-noise, high-power output characteristics. Indeed, photopolymers and other materials have been developed with sensitivities that specifically match ion laser wavelengths. As listed in Table 1, argon lasers can produce several watts of narrow-line output at several wavelengths in the UV through green. Krypton lasers have slightly lower output power, but can produce over 2 watts of single-frequency output in the red (647.1 nm) as well as lower powers at other visible wavelengths. Mixed gas (krypton/argon) lasers produce a combination of these output wavelengths.
The basic elements of a single-frequency ion laser head for holography are shown in figure 8.1. A prism is used as a wavelength filter to select the wavelength line of choice (e.g., 488 nm). Each laser output line has a typical width of 0.004-0.01 nm. This means that the coherence length of the laser is less than 50 mm. Unfortunately, successful holography requires a coherence length many times longer than the optical path difference. For most holographic applications, the line-width of the laser output must be nar...
MORE INFORMATION IS AVAILABLE IN HOLOGRAPHY MARKETPLACE 7th EDITION. ORDER YOUR COPY TODAY!