## 1 Introduction  
Since mid-infrared lasers have minimum attenuation in atmospheric transmission and cover the absorption peaks of many atoms and molecules, they are widely used in laser spectroscopy, atmosphere monitoring, photoelectric detection, remote sensing survey and many other fields [1; 2; 3; 4]. The pump laser is one of the most important key modules in tunable mid-infrared solid-state lasers. It generates a large amount of waste heat in the working process and needs to be dissipated in time, otherwise it will cause wavelength shift, decrease of output power and even damage the laser [5; 6]. Thus, it is of vital importance to dissipate the waste heat and maintain the temperature of pump laser at a suitable value. Various conventional cooling methods are used for lasers, such as water cooling, forced air cooling, thermoelectric cooling, heat pipe cooling, micro-channel cooling, compressor refrigeration and so on [7; 8; 9]. High power lasers mainly use the water cooling method to dissipate heat due to its advantages of high heat transfer coefficient and heat flux density [10]. However, it requires the connection of an external water cooler which causes the laser to have a large. Forced air cooling, heat pipe cooling, micro-channel cooling and other passive cooling methods can only ensure the temperature of the laser is higher than the ambient environment [11], while in some situations, the temperature of the laser needs to be controlled to be lower than the environment. Thermoelectric cooling, usually considered using the thermoelectric cooler (TEC), has advantages over conventional cooling devices, including being compact in size, having high reliability, no mechanical moving parts, no working liquid, light in weight, being powered by direct current, and easily switching between cooling and heating modes [12]. Due to these advantages, TECs are widely used in many fields including electronic device cooling, diode laser (LD) cooling and temperature control, domestic refrigeration, scientific equipment and so on [13; 14; 15]. In recent years, many studies have reported TEC temperature control systems for laser cooling. [PERSON] et al. [16] investigated a high power diode-side-pumped Q-switched Nd:YAG solid-state laser under 808 nm side-pumping without a water cooler. Two TECs were adopted to maintain the temperature of the LD module, and it was observed that precision of the TEC controller impacted the relative stability of the output energy. [PERSON] et al. [11] used a finite-element analysis method to study the performance of a micro semiconductor laser with TEC; the thermal cooling methods on the hot side of TEC were also investigated. [PERSON] et al. [17] developed a dynamic thermal model for a tunable laser module with a proportion-integration-differentiation (PID) temperature controller based on finite-element analysis. Temperature variation and wavelength shift of the laser were simulated by changing PID parameters and discussed. [PERSON] et al. [18] investigated a miniature thermoelectric module for pulse laser cooling, and the effects of pulse and step variable voltage on the miniature TEC module (TEM) were numerically and experimentally studied. Recent studies of thermal management using TECs for lasers have mainly focused on single diode lasers with medium and low output powers, while high output power pump lasers always use the water cooling method to dissipate heat [11], which cannot satisfy the demand for miniaturization. In this paper, an all-fiber laser pumped optical parametric oscillator (OPO) laser was established with a compact thermal control system based on an automatic temperature control circuit, TEMs, cooling fins, axial fans and heat pipes. This thermal control system was designed and analyzed in finite-element method. A mathematical model to estimate the cooling capacity of the system under different ambient environments was established.