Abstract
We propose a new method to extend the path length tunability of rotary delay-lines. This method was shown to achieve a duty cycle of >80% and repetition rates of over 40 kHz. The new method relies on a new multi-segmented micro-machined mirror and serial injection of a single reflection onto separate segments of this mirror. The tunability is provided by the relative positioning of each reflective point on the mirror segments. There are two distinct modes of operation: synchronous and asynchronous. By simply manipulating the spatial position of the returning paths over the respective mirror segments, we can switch between increasing the repetition rate (asynchronous mode) or the total delay path (synchronous mode). We experimentally demonstrated up to 8 m/s scans with repetition rates of up to 42.7 kHz. Furthermore, we present numerical simulations of 18 reflection points to illustrate possibility of achieving a scan speed of up to 80 m/s. Through intermediate combinations of synchronous and asynchronous operation modes with 4 or more passes, we also show that the system can simultaneously increase both repetition rate and scan depth.
Highlights
Mirror-based optical delay lines deliver high optical efficiency and minimal dispersion for optical interferometry applications
Using glass coverslips in the reference arm, we were able to obtain interference signals to determine the quality of the autocorrelation signal that is typically used for time resolved imaging or spectroscopy
We find that the path length resolution is 24.2 μm over 2.4 μs at a Doppler frequency of 15.2 MHz, which combined with the repetition rate leads to a scan range of 438 μm
Summary
Mirror-based optical delay lines deliver high optical efficiency and minimal dispersion for optical interferometry applications. It is worthwhile to note that delay lines using spectral shaping approaches produce high repetition rates of approximately two to four kHz while achieving tens of meters per second scan velocities They operate by shaping individual wavelengths to achieve controlled delays using reflective gratings. To overcome some of the aforementioned limitations of other delay line techniques, rotary delay lines using machined mirrors were developed and used at near infrared wavelengths for optical coherence tomography This type of delay line has proven useful for high speed terahertz time domain spectroscopy[11]. While Liu and co-workers[4] demonstrate a double-pass rotary delay line to increase path length, in their configuration and other similar approaches the repetition rate is still limited by the rotation rate of the motor and the number of mirror segments[4, 10]. Variations of this technique may be applicable to other types of multi-pass mechanical delay lines
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