Assistant Professor of Physics

Office Location 
Science Hall 336A
Mailing Address 
2083 Lawrence Road, Lawrenceville, NJ 08648

Gary  Pajer

I am a relatively new member of the Rider faculty, having recently entered academia after a fifteen year career as an industrial physicist. I’m currently in the process of building my laboratory. My interests lie in optical physics of condensed matter, opto-electronic devices (“photonics”), and nonlinear optics. Here’s a brief description of the directions in which I’ll be heading at Rider.

Optical Low-Coherence Reflectometry

Light from a highly coherent source such as a laser can be made to interfere with itself over a wide range of conditions. Interference is the addition or subtraction of electromagnetic waves that can result in destruction of the wave (if the fields subtract perfectly) or construction (if the fields add perfectly). Construction and destruction are typically observed by visualizing a series of alternate light and dark bands on an illuminated surface. In the case of completely incoherent source of light, for example an incandescent light bulb, random fluctuations of the field make perfect addition or subtraction impossible. In this case, no interference is observed.

There are field states intermediate between high coherence and no coherence. In these, interference is possible, but only under certain restrictive conditions. In low-coherence reflectometry (or interferometry) the restrictive conditions are exploited to turn the effect into a selective probe. The geometry of an optical apparatus can be arranged so that interference occurs only over a very thin disk-shaped slice of space, and furthermore, the location of the slice can be changed by adjusting the position of a mirror elsewhere in the apparatus. As a result, optical properties internal to a solid or liquid sample can be studied. There are many possible applications. Important applications that I am interested in are the study of internal structure of biological samples, transport phenomena in liquids, and the study of loss mechanisms in photonic devices.


By analogy to the word electronics, the word photonics has been coined to describe the subject of using light as a carrier of an information signal rather than electrical current as in conventional electronic devices. The field has been in development for several decades, and is now quite mature. All long distance phone calls, and many local calls are now carried on optical fiber rather than copper wire. The advantages are numerous: much higher information carrying capacity, lower weight, lower power, lower cost. There are few if any disadvantages other than the cost of changing technology from the old to the new.

Despite the fact that the technology is commonplace and ubiquitous, there is much work to be done in improving it. Components could be faster and cheaper. Noise and crosstalk can be reduced. Internal losses can be reduced allowing for longer runs between amplifiers. New signal processing needs arise. Many basic phenomena are not understood as well as they might be.

I have several interests in this field. One is the understanding of fundamental loss mechanisms. Signals are attenuated by various types of scattering, waveguide bends, and geometrical constraints. These mechanisms can be studied theoretically, and experimentally (for example by Optical Low-Coherence Reflectometry). In addition to such fundamental studies, I’m interested in device design and testing. I maintain a collaboration with Sarnoff Corporation in this effort.

Nonlinear Optics

When you shine a laser of a particular color onto a solid sample, the light reflected from the surface is the same color. Well, not entirely. An exceedingly small fraction of the reflected light has a color corresponding to twice the frequency of the incident light. This is a result of a nonlinear interaction between the electromagnetic field of the light with the electrons in the solid. In a large class of solids, those containing a center of inversion symmetry, geometrical considerations force the source of the nonlinearly reflected light to be located in a very narrow region, only a dozen or so atoms thick, at the solid’s surface. In this way nonlinear optics becomes a probe of surface geometry and surface electronic processes.

One interesting application of nonlinear optics as a probe is the study of the growth of thin films produced by deposition in vacuum. It is known from nonlinear optical studies, for example, that films that are grown at oblique angles are not deposited isotropically. There is some preferential angular ordering whose nature and origin is currently unknown. Curiously, electron microscopy cannot detect this anisotropy, thus leaving light as one of the few probes available to study this phenomenon. Furthermore, the optical technique can be set up to probe the sample in situ during the growth. It is practically impossible to do such in situ studies using electrons or x-rays.