Picosecond laser source at 1 MHz with continuous tunability in the visible red band

Abstract

Many applications in biology such as fluorescence lifetime measurements, detection of single molecules or optical tomography by time correlated single photon counting require pulsed laser sources emitting visible radiations. As the fluorescence lifetime of numerous molecules is less than a nanosecond, short pulses (around one hundred of picosecond) are needed. The repetition rate of the laser source used is an important parameter in experiments using photon counting detection chains : indeed, high repetition rates ensure a fast acquisition process of the fluorescence decay signal and allow to study of dynamic processes. However, the complex signal processing devices could not support repetition rates above several MHz without problems during the acquisition of the data. Consequently a repetition rate of 1 MHz seems to be a good requirement for this kind of applications. Another very important characteristic is the tunability of the source: in order to study different chemical species with the same laser source, it is very interesting to be able to change the wavelength easily on a broad range. There is consequently a strong need for tunable sources operating at 1 MHz in a compact and simple package. A fruitful approach to generate short visible pulses is to use a master oscillator power amplifier system operating in the near-infrared and to use non-linear processes to reach the visible range. Recent developments in passively Qswitched microchip lasers [1,2] open the way to a large number of studies on very compact and efficient pulsed sources [3][4][5][6][7]. Nevertheless, the repetition rates of the published devices are almost always in the kilohertz range. Moreover the poor efficiency of non linear materials at weak peak powers makes the development of MHz sources somewhat difficult. An interesting and successful approach is to use a fiber-based architecture and quasi-phase matched non-linear materials [8]. In this paper we present another solution based essentially on bulk elements to demonstrate a compact source providing 45 nm of continuous tunability around 660 nm with less than 200 ps long pulses. To this end, we used a Nd:YVO 4 passively Q-switched amplified microchip laser operating at 1 MHz to pump a periodically poled lithium niobate optical parametric generator. We also demonstrate 50 mW of 355 nm radiation by frequency tripling the same microlaser.Motivated by compactness and simplicity we chose as master oscillator a microchip Nd:YVO 4 laser. We used a semiconductor saturable absorber mirror to passively Q-switch the laser [9]. The repetition rate range and the duration of the pulses could then be adjusted by choosing the proper parameters for the SESAM and the design of the cavity. It can be shown that the pulse duration is directly proportional to the length of the cavity, which led us to design a very short cavity (a few hundreds micrometers) to get sub-nanosecond pulses. We used a 200 µm thick laser crystal with an antireflection coating at 1064 nm on its faces. The saturable absorber had a mo...

Lasers solides pompés par diode émettant des impulsions picosecondes à haute cadence dans l'ultraviolet

“…Les impulsions produites ont une durée de 300 ps,à une cadence continûment variable avec la puissance de pompe de 20 kHzà 1,5 MHz [5]. En raison d'effets thermiques parasites, le faisceau n'est pas limité par la diffraction et la puissance moyenne obtenue est relativement faible (autour de 50 mW pour 500 mW de pompe).…”

“…Ce dernier inconvénient peutêtre compensé par l'utilisation d'un amplificateur tel que celui qui sera décrit dans la section 3.2. On peut alors générer facilement plusieurs dizaines de milliwatts de rayonnement ultravioletà 355 nm ou 266 nm [5].…”

Generation of Picosecond Laser Pulses at 1064 nm from All Solid-State Passively Mode-Locked Lasers

“…By the progresses in directly diode-pumped solidstate laser material and by the appearance of a semiconductor saturable absorber mirror (SESAM) mode-lockers, compact ultrafast SESAM mode-locked all-solid laser systems have been strongly developed and dominating the ultrashort solid-state laser market for scientific, technological and medical applications [1][2][3][4]. This paper presents the results obtained in the development of CW diode-pumped ultrashort solid-state Nd:YVO 4 lasers passively modelocked with a semiconductor saturable absorber mirror (SESAM).…”

Broadly tunable (440–670 nm) solid-state organic laser with disposable capsules

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