# Letters

In “Simple pulse compressor compensates for misalignment” (July, p. 19) it was stated that “Rick Trebino had derived a formula for the total dispersion of an arbitrary sequence of sequence of prisms in terms of only the prisms’ dispersions and magnifications.

#### Equations for multiple-prism dispersion were derived earlier

In “Simple pulse compressor compensates for misalignment” (July, p. 19) it was stated that “Rick Trebino had derived a formula for the total dispersion of an arbitrary sequence of sequence of prisms in terms of only the prisms’ dispersions and magnifications. . . .” Although a reference is not given, this statement most likely refers to a 1985 paper published by Rick Trebino in *Applied Optics*.1 In this regard, it should be clarified that generalized equations for multiple-prism dispersion were disclosed in the open literature by Duarte and Piper in 1982 and 1983.2, 3

Indeed the generalized dispersion equations derived by Duarte and Piper were stated as a function of the beam magnification of each generalized prism, its geometry, and *dn/dλ*. Further, the presence of (±) in the mathematical series clearly offered the option of zero dispersion at a given wavelength. The second paper, written for a general audience, and published in the *American Journal of Physics*, was entitled “Generalized Prism Dispersion Theory.” As far as multiple-prism pulse compression is concerned, the equations were extended to include higher derivatives in 1987.4 The problem of dispersion perturbations due to slight beam deviations was discussed in 1990 in a paper found useful in recent experiments by European researchers.5, 6

Readers should also know that the very first demonstration of prismatic pulse compression was realized using a single-prism pulse compressor in 1983 by Dietel et al., who reported a pulse duration of 82 fs.7

In my opinion the contribution of Rick Trebino to the field was, as the title of his paper clearly stated, to discuss and outline optimal configurations for prism arrays. Since the cited opening statement is not directly attributed to Rick Trebino, I would assume that it is a simple misunderstanding. However, if left unchallenged, this misunderstanding could confuse and/or misinform the reader.

**F. J. Duarte**

Interferometric Optics

Rochester, NY

duarte@opticsjournal.com

**REFERENCES**

1. R. Trebino, *Applied Optics 24*(8), 1130 (1985).

2. F.J. Duarte and J.A. Piper, *Optics Communications 43*(5), 303 (1982).

3. F.J. Duarte and J. A. Piper, *American J. Physics 51*(12), 1132 (1983).

4. F. J. Duarte, *Optical & Quantum Electronics 19*, 223 (1987).

5. F. J. Duarte, *Optical & Quantum Electronics 22*, 467 (1990).

6. K. Osvay et al., *Optics Communications 248*, 201 (2005).

7. W. Dietel et al., *Optics Lett. 8*(1), 4 (1983).

#### Spectral Dimensions also offers commercial imaging spectrometers

John Kerekes’ article in the July issue of *Laser Focus World* (“Imaging spectrometers go commercial,” July 2006, p. 63) was very interesting. However, I was surprised to see that at least one company prominent in the commercialization of imaging spectrometers was not included in your listing; the company I refer to is Spectral Dimensions (Olney, MD; recently acquired by Malvern Instruments, but not included under either name.)

**Howard Mark**

Mark Electronics

Near Infrared Research Corp.

hlmark@nearinfrared.com