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Narrow linewidth laser diodes (LDs) emitting in the near-UV (NUV) are gaining attention for applications ranging from spectroscopy to atom cooling and interferometry or other applications requiring high spectral purity. InGaN edge-emitting LDs can exhibit a power of hundreds of mW in an unstable multimode regime detrimental to aforementioned uses. In this paper we report on a compact and robust design based on a low-cost blue LD, a beam shaping optical system and a fiber Bragg grating (FBG) acting as a wavelength selective reflector. One longitudinal mode of the non-antireflection coated laser diode is selected by a close to 30 pm bandwidth FBG allowing a few mW output power around 400 nm and a sidemode- suppression-ratio approaching 50 dB exceeding our last published results. Our previous studies showed that a single-frequency regime with a sub-MHz integrated linewidth and an estimated intrinsic linewidth of 16 kHz was possible by a carefully engineered external cavity. We will study the influence of the cavity length with different fiber types (SM or PM). Assessment will focus on the linewidth and a detailed intensity and frequency noise analysis of the emission. We will also investigate for the first-time the stability of several types of UV-FBG submitted to tens of mW of 400 nm light guided into the fiber core. This work demonstrates state-of-the-art performances by connecting low-cost components and opens the way to the fabrication of highly coherent laser sources that could meet the markets for the NUV applications.

We realize a fiber Bragg grating InGaN-based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrowband fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode suppression ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

We report on efficient diode-pumped mid-infrared lasers based on T m : L i Y F 4 , T m : Y 3 A l 5 O 12 , and T m : Y A l O 3 crystals. These lasers operate in the continuous-wave (CW) regime and deliver watt-level output power at the wavelengths of 2.2–2.3 µm (the 3 H 4 → 3 H 5 T m 3 + transition). In particular, a 1.8 at. % T m : Y A l O 3 laser pumped at 789 nm generates a maximum CW output power of 1.32 W at 2272–2277 nm with a slope efficiency of 33.1% (with respect to the absorbed pump power), a linear laser polarization ( E ∥ b ), and a fundamental transverse output mode (the measured M x 2 = 1.26 , M y 2 = 1.68 ). In the quasi-CW regime, the output peak power is scaled up to 2.69 W. The pump quantum efficiency and the fractional heat loading are estimated and discussed.

Diode lasers have been demonstrated to operate over a great part of the visible spectrum: InGaN diodes cover the violet-blue- green part ( 635 nm). Some fluorophorus in biotechnology applications are excited by intermediate wavelengths, from 540 to 630 nm. Optically pumped InGaAs lasers were demonstrated from 460 nm up to 580 nm. Standard frequency doubled diode pumped solid state (DPSS) lasers lack of suitable transition to cover the 565-650nm region. It is possible to modify the semiconductor composition to extend the frequency range or to frequency mix DPSS laser wavelengths, but it comes either with a significant R&D effort or with a complexity in the design. Raman scattering can red-shift the strong transitions of Nd or Yb lasers so that many wavelengths lying in the 1080-1300 nm range can be achieved. Recently several CW diode pumped Raman lasers were demonstrated, some of them including intra-cavity frequency doubling or mixing. The problems with these Raman lasers are the high pump threshold and the high noise. Based on monolithic cavities, we have built several visible Raman lasers with a reduced loss presenting a low pump threshold (

Single longitudinal mode visible DPSS are more and more used in devices where performance can be affected by short term (minutes) frequency drifts and hops. Long exposure holography and Raman spectrometry are applications requiring high frequency stability. Resonant external cavity frequency doubling (to generate CW deep UV) and pumping doubly resonant OPOs may be even more demanding applications in terms of frequency stability. Mechanical vibrations and thermal fluctuations are usual sources of short term frequency variations or instabilities. Monolithic ring cavities (such as NPRO) are known to solve this problem but they are quite expensive to manufacture. We will show that much simpler linear monolithic cavities used in our standard product line (SLIM-532, SLIM-550, SLIM-561 and SLIM-660) present best of class frequency stabilities compatible with the most demanding applications. Frequency tuning capabilities will be discussed and could be used in an active stabilization of the laser. Some applications can benefit from long term wavelength stability as well. Raman spectra can be monitored without control of the pump wavelength if the long term stability is good. In addition, narrow filters can be used to measure small Stokes shifts. We are monitoring several monolithic laser sources. After more than 6000 hours of operations, the wavelength shift is within 1 pm. The laser source has been restarted more than 1000 times without any change of the operating wavelength. Finally, thermal cycles do not impact the wavelength. In conclusion, we demonstrate that monolithic linear cavities are best suited for all applications requiring wavelength stability.

Diode pumped frequency doubled Nd :YAG microchip lasers should become an alternative to air-cooled argon ion lasers. The main issues to be solved are the long-term stabilization of the single frequency operation and the power control of the multi-frequency operation. These questions are mostly related to the laser dynamics. In this paper, we present an accurate modelling of the laser dynamics, including quenching processes, non uniform pumping, partial overlap of optical signals and excited-state populations, hole burning and type-I frequency doubling. We theoretically predict that even in multimode operation, only one mode is oscillating at a time, with a mode hoping at a rate of about 50 kHz. This behavior, quite different from the well known dynamics of intra-cavity type-II frequency doubled lasers (green noise) is experimentally confirmed. Diode pumped frequency doubled Nd:YAG 473 nm lasers based on a simple linear cavity are built and exhibit high output power (90+ mW) and record slope efficiency (45% with respect to absorbed power). The understanding of its 2-mode operation allowed us to stabilize the average output power. A similar laser was operated on a single frequency. No wavelength drift could be measured and no mode hopping was observed over 24 hours.

conference 5332 « Solid State Lasers XIII: Technology and Devices », session 5 « Compact Laser Sources » [5332-21]; International audience; Although powerful (2.8 W) blue emission at 473 nm was recently reported, the design of low-cost compact and efficient 473 nm source failed so far. We have theoretically and experimentally analyzed the operation of a simple 2.1 mm long microchip assembly pumped by a 100x1 μm laser diode and found several ways to improve the efficiency of such a laser. As a first result, we achieved high beam quality (M2