We present a new light source capable of locating interference fringes at an adjustable distance from the interferometer. The spectrum is electronically controlled in such a way that the fringes are limited to only one of the surfaces of the optics under test. With the new source it is straightforward, for example, to measure the parallel surfaces of thin glass plates and multiple surface cavities. Existing interferometers, as well as older systems, can be upgraded with this source.<p> </p> Traditional methods of interferometry are widely used and accepted for simple measurement configurations, but measurement accuracy can decrease rapidly with increasing measurement complexity. For example, coherent interferometry struggles to achieve accurate and repeatable results with the presence of any additional feedback surface in the measurement cavity due to temporally coherent back reflections. Conversely, incoherent interferometers can isolate single surfaces for measurement but require more complex interferometer system designs. As a result, many of these systems are limited in their dynamic range of measurable cavity sizes and present considerable difficulties in the alignment process, increasing total measurement time. Both methods are inherently restricted by the intrinsic properties of their respective source. <p> </p>Spectrally controlled interferometry (SCI) is a source driven method which inherits many advantages from both coherent and incoherent interferometry while evading typical limitations. The sources spectral properties are manipulated to produce a tunable coherence function in measurement space which allows control over the coherence envelope width, the fringe location, and the fringe phase. With this source realization, a host of measurement advantages which simplify measurement complexity and reduce total measurement time becomes available. One major application is the extinction of extraneous surface back reflections. Without any mechanical translation, realignment, or traditional piezoelectric transducers, front and back surfaces of planar optics can be isolated independently and complete phase shifting interferometric (PSI) measurements can be taken. Furthermore, because all control parameters are implemented at the source level, the spectrally controlled source is a good candidate for upgrading existing interferometer systems. <p> </p>In this paper, we present the theoretical background for this source and the implications of the method. Additionally, a multiple surface cavity measurement is provided as a means of demonstrating the spectrally controlled sources capability to isolate individual cavities from detrimental back reflections across a large dynamic range of measurable cavity sizes without mechanical realignment. A discussion of the implementation benefits and practical details will be included. Limitations and comparisons to alternative methods will be addressed, as well.
We demonstrate the use of two ultrafast fiber laser systems locked together at identical repetition rates of 100 MHz to
achieve a timing resolution below 300 fs for pump-probe experiments. By sweeping the set-point of the locking
electronics, we scan the time delay between the individual pulse trains by 800 ps. This scanning technique requires only
sub-micrometer mechanical motion. Since the temporal scan range is determined electronically, the acquisition can be
limited to regions where meaningful physical data is recorded. We discuss how our technique can approach
asynchronous optical sampling based on GHz repetition rate lasers in terms of data collection efficiency while offering a
number of practical advantages.
We present an overview of nonlinear frequency conversion techniques which we developed and optimised for use with
mode-locked Erbium fiber lasers. Starting with 70 fs, 3 nJ pulses at 1560 nm, we access the entire wavelength band from
500 to 2000 nm without gaps. Across this broad range of wavelengths, we adapt pulse parameters such as temporal
duration and spectral width to the specific application requirements.