Abstract
One of the major factors that limits the widespread use of ultrafast titanium sapphire (Ti:S) lasers in life science is its expensive and complex pump source. Broad area diode laser (BA-DL) based pump sources have high potential to solve this problem, since they are compact, inexpensive and very efficient. However, their non-diffraction limited beam profile makes it challenging to achieve high powers in Kerr-lens mode-locked (KLM) operation of Ti:S lasers. In this work, we show that the ideal way to beam shape two spectrally combined BA-DLs with different beam qualities is to aim for a compromise between matching to the cavity mode diameter and the cavity mode Rayleigh range. We furthermore conclude that the relative intensity noise (RIN) of the BA-DL pumped Ti:S laser, another important parameter for imaging applications, is sufficiently low for a wide range of life science applications. However, for applications that are highly sensitive to noise, new laser diode designs are likely necessary to reduce inherent noise originating within the laser diode.
Highlights
Having the capability of generating femtosecond pulses with broad spectral tuning range starting from ∼650-1100 nm, the ultrafast titanium sapphire (Ti):S lasers play a major role in the development of many biophotonic imaging technologies, like optical coherence tomography [1,2,3] and multiphoton imaging [4,5,6], for the diagnosis of different types of early stage cancers [7,8,9]
The optimum focal diameters for both Broad area diode laser (BA-DL) were found to be at the point where their matching Rayleigh lengths ∼1.2 mm were very close to the Rayleigh length of the cavity mode ∼1.5 mm
It has been shown that careful beam shaping before wavelength-multiplexing of two BA-DLs with very different beam qualities leads to efficient pumping of a Kerr-lens mode-locked (KLM) Ti:S laser
Summary
Having the capability of generating femtosecond pulses with broad spectral tuning range starting from ∼650-1100 nm, the ultrafast Ti:S lasers play a major role in the development of many biophotonic imaging technologies, like optical coherence tomography [1,2,3] and multiphoton imaging [4,5,6], for the diagnosis of different types of early stage cancers [7,8,9] In these applications, the intensity noise of the Ti:S laser play an important role in order to achieve a high signal-to-noise level and good image contrast [10,11] Traditionally, frequency-doubled diode-pumped solid-state lasers (DPSSLs) operating in the green wavelength region have been used for pumping of the Ti:S lasers. The intensity noise of BA-DL pumped Ti:S is not far from the frequency-doubled tapered laser pumped Ti:S, which makes the BA-DL pumped Ti:S laser a good candidate for bio-imaging [25]
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