This volume contains notes based on the lectures delivered at the fourth New Zealand Symposium in Laser Physics, held at the University of Waikato, Hamilton, February 10-15, 1986. At this meeting, about 80 physicists work ing in many parts of the world met to discuss topics of current interest in contemporary laser physics and quantum optics. These symposia, which have been held triennially since 1977, have evolved into an important meet ing ground for experimentalists and theoreticians working in a very rapidly developing field. As the format has evolved, the number of participants, in cluding the number from overseas, has grown steadily, and this year a poster session was included for the first time, enabling a far greater range of topics to be discussed than was possible in the limited lecture time available. At this meeting the major interest of the participants concerned the the oretical investigation of squeezed states of the radiation field and the very recently reported experimental observations of such states. Other related ar eas of work reported here include bistability and chaotic behaviour of optical systems, the quantum theory of measurements, optical tests of general rel ativity, and the current technological limitations governing the stabilization of lasers. The editors would like to thank the participants for providing detailed notes for publication shortly after the meeting, and the various organisa tions that have provided financial support."

This volume contains contributions based on the lectures delivered at the Fifth International Symposium on Quantum Optics. This Conference, the fifth in a tri ennial series hosted in New Zealand, was held in Rotorua, 13-17 February 1989. The Conference was attended by 75 participants from New Zealand, Australia, Japan, USA, France, Italy and Germany. There was also a high level of par ticipation from graduate students from New Zealand and Australia, who greatly benefitted from the opportunity to attend world-class conferences. The partici pants were housed in the Hyatt Hotel and surrounding motels and all enjoyed the relaxed atmosphere offered by Rotorua in the Southern Hemisphere summer. There were 24 invited papers, given as oral presentations of 40 minutes, and 22 poster papers. The major topics covered at the Conference were new experimental and theoretical results in nonclassical light, including sub-shot-noise light sources. We were fortunate in that all major experimental groups in the world working in this area were represented. The latest experimental results from AT & T Lab oratories, NT & T Laboratories, mM Laboratories, Ecole Normale Superieure and the Californian Institute of Technology were reported. New theoretical results from Southern Hemisphere participants included a true phase operator for quantum fields derived by Professor David Pegg of Griffiths University and a general treat ment of lasers pumped without shot noise by Professor D. F. Walls of Auckland University.