It is well known that electromagnetic fields are important probes of the properties of matter. We can learn about atomic molecular energy levels by studying the absorption, emission, and scattering of electromagnetic waves. For example, the rate at which a system absorbs energy and its dependence on the frequency of the electromagnetic field gives information on the allowed transitions. From such studies one can determine the energy levels and their lifetimes. Similarly, scattering processes provide a wealth of information. The traditional probing of matter is restricted to weak fields; however, in Chapter 11 we saw how strong fields dress the energy levels of a system. Strong fields also modify the transition rates. In order to study the characteristics of such modifications we need to probe a coherently driven system using a probe field. In this chapter we study the absorption, emission, and scattering processes in strongly driven systems. A novel characteristic of radiation from strongly driven systems is its nonclassical nature.

Effects of relaxation: optical Bloch equations

So far we have considered only interactions with external electromagnetic fields. In reality, one has to account for various sources of decay of the atomic population and coherences. For example, an atom can decay radiatively by emitting a photon. The resulting collisions change the populations and coherences. In Chapter 9 we discussed in detail how various relaxation processes can be included from first principles in the master equation framework.

Dipole–dipole interactions between atoms or molecules profoundly affect the light absorption that occurs in matter. The spectral characteristics of light absorption can be strongly modified. For example, the weak field absorption spectrum splits into a doublet [1]. The separation of the doublet depends on the strength of the dipole–dipole interaction. Furthermore, the photon antibunching exhibited by a single-atom fluorescence starts becoming bunching due to a nearby atom [2]. The dipole–dipole interactions also give rise to fascinating applications in quantum information science, such as quantum logic operations in neutral atoms [3]. The dipole–dipole interaction can transfer excitation from one atom to the other and this transfer process produces entanglement between two atoms. For two atoms with the first one in the excited state ∣eA, gB⟩, the excitation would be on the atom B, i.e. ∣eA, gB⟩ → ∣gA, eB⟩ after a certain time. Clearly halfway through one would expect the state of the two atom system would be of the form (∣eA, gB⟩ + ∣gA, eB⟩)/√2, which is a state of maximum entanglement The dipole–dipole interaction is known to aid the process of simultaneous excitation of two atoms leading to the possibility of nanometric resolution of atoms [2, 4–6]. There are other types of dipole–dipole interactions, such as van der Waal interaction [7] which involves two atoms each in a state, which could be an excited state or the ground state.

This chapter is devoted to the dynamical evolution of open quantum system [1–3]. An open quantum system is one where it interacts with the environment. A system undergoing relaxation is an example of an open quantum system. We have already come across an example of open quantum system in Chapter 7 where we have discussed spontaneous emission from a two-level system. The two-level system interacts with the vacuum of the electromagnetic field. The vacuum consists of infinite number of modes and is a large system. The vacuum in this case is the environment. The population in the excited state decays. A photon is emitted and the emitted photon leaves the vicinity of the atom, i.e. the emitted photon is not reabsorbed by the atom. Another example of an open system is the case of atoms colliding with the atoms of a buffer gas. Here the buffer gas is the environment. Other examples of open systems are the fields confined in the cavities. The case of ideal cavities, i.e. cavities bounded by mirrors with 100% reflectivity, is uninteresting. We need the photons from the cavity to leak out in order to learn about the photons in the cavity. Thus we need to have mirrors with nonzero transmission. In this case, the electromagnetic field inside the cavity couples to the vacuum modes outside the cavity; thus the vacuum outside is the environment.

In this chapter we will show how many concepts from quantum optics, such as squeezing, nonclassicality, and quantum entanglement, can be applied to nano-mechanical systems leading to the possibility of realizing the quantized behavior of macroscopic systems [1]. Furthermore, nano-mechanical systems can exhibit a variety of rich nonlinear phenomena as the basic interaction between the nano-mechanical system and the radiation fields is via radiation pressure [2]. This interaction is nonlinear. Thus many nonlinear processes such as electromagnetically induced transparency, optical bistability, and up-conversion of radiation are expected to occur for nano-mechanical systems. Similarly, cavity QED effects such as vacuum Rabi splittings are also expected to occur provided one can design systems such that the interaction of a single photon with the nano-mechanical mirror is large. We note that the work on nano-mechanical systems originated with the discussion of Braginsky and collaborators [3] on how to measure small forces accurately. In this chapter, we will discuss only the fundamental quantum and nonlinear optical effects in nano-mechanical systems interacting with quantized and semiclassical fields.

Introduction

Hormones are chemical signals that are produced by the insect and circulate in the blood to regulate long-term physiological, developmental and behavioral activities. These signals complement those of the nervous system, which provides short-term coordination. The activities of the two systems are closely linked and sometimes not clearly distinguishable. General aspects of hormones are discussed in this chapter, including their chemical structures (Section 21.1); endocrine organs that secrete hormones (Section 21.2); the means by which hormones are transported in the hemolymph (Section 21.3); regulation of hormone titers (Section 21.4); and the mode of action of hormones on their target tissues (Section 21.5). Specific actions of hormones regulating particular functions are considered in other chapters; notable examples include molting and metamorphosis in Section 15.4, yolk synthesis in Section 13.2.4, embryonic cuticles in Section 14.2.10, diuresis in Section 18.3.3, mobilization of fuel for flight in Section 9.6.2, polyphenism in Section 15.5 and diapause in Section 15.6.

Chemical structure of hormones

Apart from molting hormones (polyhydroxylated steroids) and juvenile hormones (sesquiterpenes), most known insect hormones are polypeptides. Some biogenic amines are also known to function as hormones (see Section 20.2.3).

Introduction

Insects and other arthropods are built up on a segmental plan, and their characteristic feature is a hard, jointed exoskeleton. The cuticle, which forms the exoskeleton, is continuous over the whole of the outside of the body and consists of a series of hard plates, the sclerites, joined to each other by flexible membranes, which are also cuticular. Sometimes the sclerites are articulated together so as to give precise movement of one on the next. Each segment of the body primitively has a dorsal sclerite, the tergum, joined to a ventral sclerite, the sternum, by lateral membranous areas, the pleura. Arising from the sternopleural region on each side is a jointed appendage.

In insects, the segments are grouped into three units, the head, thorax and abdomen, in which the various basic parts of the segments may be lost or greatly modified. Typical walking legs are only retained on the three thoracic segments. In the head, the appendages are modified for sensory and feeding purposes and in the abdomen they are lost, except that some may be modified as the genitalia and in Apterygota some pregenital appendages are retained. This chapter introduces the structures of the head (Section 1.1), neck (Section 1.2) and antennae (Section 1.3). Chapter 2 concerns the mouthparts and feeding.

Preface

Reginald Chapman's The Insects: Structure and Function has been the preeminent textbook for insect physiologists for the past 43 years (since the moon landing, in fact). For generations of students, teachers and researchers The Insects has provided the conceptual framework explaining how insects work. Without this book, the lives of entomologists worldwide would have been substantially more difficult. Nevertheless, the most recent (fourth) edition of this remarkable book was published in 1998, and a great deal has happened since then. Sadly, Reg died in 2003 and there was no reasonable prospect of any other person taking on the next revision single-handed. We have decided to take a different approach: to invite a team of eminent insect physiologists to bring their expertise to the collective enterprise of writing the fifth edition of The Insects.

Our aim has been to protect the identity of The Insects by working with Reg's original text. Certain areas have needed more revision than others, and some sections have been shrunk to accommodate advances in others. Our sole major deviation from the style of previous editions has been to remove all citations to primary literature from the main text. These in-text citations had accreted across successive revisions, and were somewhat patchy in coverage throughout the book. With the availability of online literature search engines today, students and researchers alike are better served by a short list of key references at the end of each chapter to provide a lead-in to the literature.